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Agriculture Handboo-k No. 134

QUEFNS BOROUGH
PUBLIC LIBRARY

AUG 3 1976

i'epository Document

MAPLE SIRUP
PRODUCERS
MANUAL

UNITED STATES DEPARTMENT OF AGRICULTURE • AGRICULTURAL RESEARCH SERVICE

From the collection of the

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0 Prejinger
V Jjibrary

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San Francisco, California
2008

AGRICULTURE HANDBOOK NO. 134

MAPLE SIRUP PRODUCERS MANUAL

c. o. waiits

and
Claude H. Hills

Agricultural Research Service
UNITED STATES DEPARTMENT OF AGRICULTURE

Issued November 1963

Revised June 1965

Washingtoa D.C. Slightly revised July 1976

For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402 - Price $2.50
25% discount allowed on order of 100 or more to one address
Stock Number 001-000-03504-5

ACKNOWLEDGMENTS

The authors acknowledge the technical assistance of M. C. Audsley, H. G.
Lento, A. J. Menna, T. S. Michener, J. Naghski, W. L. Porter, E. E. Stinson, and
J. C. Underwood of the Eastern Regional Research Center, Agricultural Research
Service; and F. E. Winch, Jr., Cornell University; the research work of J. W. Marvin
and his associates at the University of Vermont; P. W. Robbins and R. N. Costilow
and their students at the Michigan State University; and John Hacskaylo and
James Callander, Ohio State Experiment Station; the cooperation of Lloyd M.
Sipple, Bainbridge, N.Y., in developing and testing new equipment and procedures;
and the facilities and equipment made available by the following maple sirup
producers and equipment manufacturers; John Zimmerman, George Keim, Rey-
nolds Sugar Bush, A. C. Lamb and Sons, Grimm Evaporator Company, Vermont
Evaporator Company, George Soule Company, Gary Maple Sugar Company, and
General Foods Corporation. The authors express their thanks for the assistance,
support, and encouragement given in the preparation of this handbook by the
National Maple Syrup Council, P. A Wells, C. F. Woodward, and Mrs. PhyUis K
Davis.

Trade names are used in this handbook solely to provide specific information.
Mention of a trade name does not constitute a guarantee or warranty of the
product by the U.S. Department of Agriculture or an endorsement by the
Department over other products not mentioned

CONTENTS

Economics ^ 3

Sugar maples 4

The sugar grove 4

Sap yields 6

Summary 8

Tapping the tree 8

Date of tapping 9

Selecting trees 9

Boring tapholes 9

Life of a taphole 11

Sanitizing tapholes 12

Summary 14

Spouts and buckets 14

Sap spouts 14

Rainguards 16

Sap buckets and bags 16

Summary 18

Collecting the sap 18

Collecting tanks 19

PipeHnes 20

Summary 22

Plastic tubing 23

Installing tubing 24

Taking down tubing 28

Washing and sanitizing tubing 29

Reinstalling tubing 33

Summary 34

Vacuum systems 35

Storage tanks 35

Summary 37

Evaporator house on the sap-producing farm 37

Location 37

Function 38

Requirements 38

Design 38

Steam ventilation 38

Location of evaporator 41

Air supply 42

Sirup-processing room 42

Fuel storage 42

Summary 43

The evaporator and its function 43

Design of evaporator 44

Changes in sap during its evaporation to sirup 44

Evaporation time 45

Liquid level in evaporator 46

Rates of evaporation 47

Rule of 86 48

Summary 48

Operating the evaporator , 49

Starting the evaporator 49

Drawing off the sirup 49

Finishing pan 50

Page

Automatic drawoff 51

End of an evaporation 52

Cleaning the evaporator 53

Summary 55

Other types of evaporators 55

Steam evaporator 55

Vacuum evaporator 57

Summary 57

Fuel 58

Wood 58

Oil 58

Summary 65

Maple sirup 65

Composition of sap and sirup 65

Color and flavor 67

Buddy sap and sirup 68

Rules of sirupmaking 70

Grades of sirup 70

Summary 71

Control of finished sirup 71

Viscosity of maple sirup 71

Effect of temperature on viscosity 72

Old standards of finished sirup V2

Use of precision instruments 72

Elevation of boiling point 72

Finishing pan 74

Special thermometers 75

Hydrometers 76

Summary 78

Clarification of sirup 78

Sugar sand 78

Sedimentation 79

Filtration 79

Summary 81

Checking and adjusting density of sirup 82

Weight method 82

Refractometry method 82

Hydrometry method 82

Measuring density 85

Measuring solids content 86

Adjusting density 87

Summary 88

Grading sirup by color 89

Color standards 89

U.S. color comparator 89

Summary 90

Packaging 90

Stack burn 91

Control of micro-organisms 91

Size and type of package 92

Summary 92

Standards for maple sirup for retail sale 93

Summary 94

Maple products 94

Equipment 95

Maple sugar 96

Maple cream or butter 98

Fondant 100

Soft sugar candies 100

Maple spread 105

Fluffed maple product 106

High-flavored maple sirup 106

Crystalline honey- maple spread 109

Other maple products ^ 109

Summary 110

Testing maple sirup for invert sugar 113

Simple test H"^

Quantitative test 114

Determining invert sugar content of sirup 115

Summary 115

PaRC

The central evaporator plant 116

Location 117

Size 117

Design 117

Operation 118

Sap suppliers 120

Purchase of sap 121

Storing sap 122

Handling and storing sirup 124

Sanitation 125

Economics 125

Standardizing sirup for color and density 126

Custom packaging and gift packages 126

High-flavored and high-density sirup 127

Manufacture of confections 127

Summary 128

References cited 128

Supplemental reading 134

MAPLE SIRUP PRODUCERS MANUAL

By C. O. WILUTS" and CLAUDE H. HILLS, Eastern Regional Research Center, Northeastern Region, Agricultural Research

Service

No one knows who first discovered how to
make sirup and sugar from the sap of the
maple tree. Both were well-estabhshed items of
barter among the Indians Hving in the area of
the Great Lakes and the St. Lawrence River,
even before the arrival of the white man {36,
10 IV

The maple crop, one of oui- oldest agricultural
commodities, is one of the few crops that is
solely American. Until only a few years ago, it
was both produced and processed entirely on
the farm.

The last 20 years have witnessed some vast
changes in the maple sirup industry. For the
first half of this century, maple sap was col-
lected and converted to sirup in much the same
way as it was in 1900, when atmospheric evapo-
ration equipment was developed by Yankee
ingenuity (56). Many of the more recent
changes have been the result of scientific and
engineering studies carried out by the Eastern
Regional Research Center in Philadelphia, Pa.,
and by the experiment stations and agricul-
tural colleges of Michigan, New Hampshire,
New York, Ohio, and Vermont. Recently the
Forest Service has established a facility for
research on maple sirup production at the
Northeastern Forest Experiment Station in
Burlington, Vt.

Maple sirup is a woodland crop. Since the
trees grow best at altitudes of 600 feet and
higher, maple sirup is usually produced in hilly
country. Its production is a vital part of the
local economy in dozens of communities from
Maine westward into Minnesota, and south to
Indiana and West Virginia (chart 1). The same
type and quality of maple products are pro-
duced throughout the area.

' Retired February 1969.

- Italic numbers in parentheses refer to References
Cited, p. 128.

Chart l.^A and B , range of hard maple trees; A, range of
commercial production of maple sirup.

Maple sirup, like other crops, is subject to
yearly fluctuations in production because of
climatic and economic conditions. Production in
the past has been affected by the cost or supply
of white sugar and by the supply of farm labor.
In 1860, a record crop of 4,132,000 gallons of
maple sirup was produced. For the next decade
the price of cane sugar declined. Production of
maple sirup also declined to a low of 921,000
gallons in 1869. As cane sugar became scarce
during World War I, production of maple sirup
again rose, slightly exceeding the 1860 record.
Production also increased during World War II.
Since then, production has decreased (table 1)
(125, 126).

The decreased production since World War II
is a reflection of the shortage of farm labor

2 AGRICULTURE HANDBOOK 134, U.S. DEFT. OF AGRICULTURE

Table L — Maple sugar and sirup: Trees tapped, production, average price received by farmers,
and imports. United States, selected years, 1918-70 '

Trees
tapped

Production

Price '

Imports for
consumption

Year

Sugar
made

Sirup
made

Total
product in
terms of
sugar ■ ,

Average total
product per tree

As sugar ' As sirup -

Per

pound

- of sugar

Per
gallon
of sirup

Sugar

Sirup '

1918

1,000 trees
.. 17,053
.- 14,070
.- 13,158

- 12,341
._ 9,970

- 7,685
-- 8,090
__ 6,138

1,000

pounds

11,383

3,238

2,134

1,241

394

202

246

1,000

gallons

4,141

2,817

3,712

.3,432

2,601

1,030

2,006

■■^ 1,578

^ 1,124

1,266

1,110

1,000
pounds
44,511
25,774
31,830
28,697
21,202

8,442
16,302
12,624

8,992
10,128

8,880

PouTids
2.61
1.83
2.42
2.33
2.13
1.10
2.02

Gallons
0.33
.23
.30
.29
.27
.14
.25
.26

Cents

Dollars

1,000
pounds
. 3,807
3,911
9,735
1,920
4,087
4,131
6,549
6,024
5,742
4,688
3,561

1,000
pounds

1925

1930

1935

1940

1945

1950

1955

26.9
30.2
26.7
29.4
54.6
77.2

2.08
2.03
1.42
1.65
3.21
4.12
4.68
4.96
5.04
6.83

113
1,575
2,469
4,660
1,232
5,282
5,044

10,009
9,700

10,549

1960

1965

1970

' For 1918-40, production estimates for Maine, Maryland, Massachusetts, Michigan, New Hampshire, New York. Ohio,
Pennsylvania, and Vermont; in 1945 Minnesota was added.

- Assuming that 1 gallon of sirup is equivalent to 8 pounds of sugar.

'Obtained by weighting State prices by quantity sold from 1945 to date; prior to 1945 weighted by production.

I A gallon of sirup weighs about 11 pounds.

' Includes sirup later made into sugar.

SOURCES: Data for 1918-50 from Agricultural Statistics, 1957, table 133 {125). Data for 1955 and 1960 from Statistical
Reporting Service and Economic Research Service, for 1965 and 1970 from Agricultural Statistics, 1972. table 137 (128).

during this period. Although the trend in the
country as a whole is downward, production of
maple sirup in Michigan, Minnesota, and Wis-
consin has increased. In fact, based on the
number of tappable trees, production in these
States could exceed production in New York
and the Northeastern States. For example,
Michigan has one-fifth of the total stand of
maple trees. Canada's total maple crop is about
double that of the United States.

Table 2 shows the number of maple trees of
tappable size and the percentage tapped in
1951.

Surveys in the eastern maple-producing
areas (126) of the number of maple trees tapped
as well as the total number of tappable size
have shown that the industry is not suffering
from too few trees. Although many sugar ma-
ples have been cut for lumber, vast stands
remain, and these stands can supply our maple
sirup needs.

Table 3 shows the production of maple sugar
by the 11 principal States for selected years,
1926-71.

Table 2. — Tappable maple trees, and trees
tapped. Eastern States, 1951

State

Tappable
trees '

Trees tapped

Thousands Number Percent

Maine 53,553 136,000 0.25

Maryland 1,660 28,000 1.7

Massachusetts 11,913 166,000 1.4

New Hampshire 12,103 261,000 2.2

New York 73,128 1,960,000 2.7

Pennsylvania 33,553 422,000 1.3

Vermont 25,840 3,118,000 12.1

West Virginia 13,031

' Larger than 10 inches in diameter at breast height.

MAPLE SIRUP PRODUCERS MANUAL

Table 3.— Rank of States in production of maple sugar, selected years, 1926-71

Rank

1926

1931

1936

1941

1946

1951

1956

1961

1966

1971

N.Y.

Vt.

N.Y.

Ohio

Pa.

Mich.

Wis.

N.H.

Mass.

Md.

Maine

Vt.

N.Y.

Ohio

Pa.

Mich.

Wi^.

N.H.

Mass.

Md.

Maine

Vt.

N.Y.

Ohio

Pa.

Mich.

Mass.

N.H.

Wis.

Maine

Md.

Vt.

N.Y.

Ohio

Mich.

Pa.

N.H.

Mass.

Wis.

Maine

Md.

Vt.

N.Y.

Pa.

Mich.

Mass..

N.H.

Wis.

Maine

Md.

Ohio

_Minn.

Vt.

N.Y.

Ohio

Pa.

Wis.

Mich.

N.H.

Mass.

Md.

Maine

Minn.

Vt.

N.Y.

Ohio

Wis.

Mich.

Pa.

N.H.

Mass.

Md.

Maine

Minn.

N.Y.

Vt.

Wis.

Pa.

Mich.

Ohio

N.H.

Mass.

Md.

Minn.

Maine

N.Y.

-. Vt.

Vt.

- Ohio

Ohio

Pa.

Mich.

N.H.

Wis.

Mass.

N.H.

_. Wis.

Mass.

Maine

Md.

ECONOMICS

Maple sirup, a noncultivated, nonfertilized
crop derived from trees of the farm woodlot,
provides supplemental cash incomes for many
farmers, and it is the major cash crop for some
farmers {2A, 26, 132, lUO, U2). The trees on 1
acre will provide 160 tapholes and an average
yield of 1 quart of sirup per taphole, or 40
gallons of sirup per acre. At $10 per gallon, this
sirup provides an annual per-acre gross income
of $400.

With the advent of the central evaporator
plant, maple sap became a marketable commod-
ity. Annual gross income for sap ranges from
900 to $2.50 per taphole for sap delivered at the
evaporator plant.

The maple season is short and comes in the
early spring when most other farm activities
are slowest. Thus, it does not compete with
other farm activities. Because the season oc-
curs when off-farm employment is at a seasonal
low, it fits well into a part-time farming pro-
gram.

Surveys in New York (5, 8), Ohio (63), Michi-
gan {92), and Wisconsin (113) have shown that
earnings from the production of maple sirup
are among the highest on the farm. Wages
average $3 per hour with a high of more than
$5 for every hour spent in cleaning equipment,
tapping trees, installing and taking down equip-
ment, and collecting and boiling the sap.

With the high annual cash crop and high
wages earned in producing sap and sirup, it is
difficult to understand why only 1 of 20 tappa-
ble maple trees is being utilized. However, until

recently maple sirup production methods were
antiquated, at least when compared to modern
methods of crop and livestock farming, and the
unfavorable working conditions made sap col-
lection and sirupmaking unattractive.

Both equipment and processing methods are
being modernized. Modernization should do
much toward making maple sap and sirup pro-
duction more attractive (71, U3). This moderni-
zation includes plastic pipelines for collecting
and transporting sap; taphole germicidal pel-
lets; sanitary practices in tapping and sap han-
dling; oil-fired evaporators; improved methods
for evaporating sap, filtering sirup, and packag-
ing the products; and the central evaporator
plant. All these changes have reduced labor
requirements and production costs, and have
contributed to producing better grades of sirup
that have a correspondingly greater value. Be-
cause of the relatively high fixed costs for
producing sirup on the farm, net income may be
too low when sap from fewer than 500 tapholes
is available, and the sap could be more profita-
bly sold to a central plant.

Sirup can be sold immediately to produce
ready cash, or it can be held for a more favora-
ble market or as a supply of raw material for
producing more profitable maple products. If
the sirup is held, it can be used as collateral for
short-term loans.

Since 1940, the proportion of the maple sirup
produced in the United States that has been
sold directly to the consumer by the producer

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

has increased. In many instances this has in-
creased returns for the producer. To stabilize
this expanded outlet, the producer has im-
proved the appearance of the package and the
quality of the sirup so that it meets State and
Federal specifications. Many producers are ob-
taining larger returns by converting their sirup
to confections such as maple cream and hard
and soft sugar candies. "^

Maple sirup producers" have formed associa-
tions so they can pool their stocks. The chief
functions of these associations are to maintain
adequate supplies, to promote sales, and to
maintain the quality of the products. A number
of communities hold annual festivals to stimu-
late interest in maple items.

The central evaporator plant has made it

possible for the first time to separate sap pro-
duction from the processing of sap to sirup.
Thus, farmers can realize a substantial income
from maple sap without having to make large
capital investments m an evaporator house, an
evaporator, sap storage tanks, and miscella-
neous equipment.

The States, in cooperation with the Agricul-
tural Research Service and the Extension Serv-
ice of the U.S. Department of Agriculture, are
conducting strong extension programs. These
programs have brought the results of research
directly to maple producers. In New York, a
leader in this progranri, it is not uncommon for
more than a thousand producers to attend the
annual "maple sirup" schools held throughout
the State in the premaple season.

SUGAR MAPLES

Only 2 of the 13 species of maple (Acer) native
to the United States are important in sirup
production (6, 55, 12i, 157).

Acer saccharum Marsh, (better known as
sugar maple, hard maple, rock maple, or sugar
tree) furnishes three-fourths, of all sap used in
the production of maple sirup. Although this
tree grows throughout the maple-producing
areas (chart 1), the largest numbers are in the
Lake States and the Northeast. Trees grow
singly and in groups in mixed stands of hard-
woods. The trunk of a mature tree may be 30 to
40 inches in diameter. The tree is a prolific
seeder and endures shade well but unfortu-
nately does not grow rapidly. It is best distin-
guished by its leaf (chart 2).

Acer nigrum Michx. F. (black sugar maple,
hard maple, or sugar maple) grows over a
smaller range than does A. sacchamm. It does
not grow as far north or south but is more
abundant in the western part of its range. This
tree is similar to A. saccharum in both sap
production and appearance. Its principal distin-
guishing feature is the large drooping leaf of
midsummer (chart 2).

Other species of maples commonly found in
our hardwood forests are the red maple Acer
rubrum L.) and the silver maple (A. saccha-
rinum L.). These trees, readily identified by
their leaves (chart 2), are not good sources of

RED MAPLE "' SILVER MAPLE

Chart 2. — Leaves of the sugar maple (Acer saccharum
Marsh.), red maple (A. rubrum L.), silver maple (A.
saccharinum L.), and black maple (A. nigrum Michx.

F.).

maple sirup because their sap is less sweet than
that of A. saccharum and A. nigrum, and it
often contains excessive amounts of sugar sand.
The red maple, the more common of the two, is
easily identified in the spring by the red color of
its buds.

The Sugar Grove

Most maple sugar groves, commonly called
sugar bushes, are parts of stands of old hard-

MAPLE SIRUP PRODUCERS MANUAL

wood forests. In the ideal sugar grove, most of
the other trees have been cut out and the
maples have been thinned sufficiently to allow
the trees to develop a good crown growth (,63).
Thinning should be done according to a care-
fully planned program, with the assistance of
the State extension forester and the State for-
ester for the area. If the stand is made up
entirely of maples, approximately the same vol-
ume of sap is produced per acre regardless of
the size of the trees (^6). As the number of trees
per acre decreases below 160 trees 10 inches in
diameter at breast height (d.b.h.) or 40 trees 25
inches d.b.h., the size of the crovvTis and the
yield per tree may increase but the cost of
collecting sap also increases because the dis-
tance between trees requires longer sap mains
when tubing is used, and sap collected by hand
must be carried farther.

Figures 1 and 2 show a maple grove with the
large full crowns that are so important to the
production of large amounts of sweet sap.

For maximum returns, the grove should con-
tain at least SOOtapholes, that is, a minimum of
500 trees 10 inches d.b.h. Groves with fewer

than 10 maple trees per acre are not profitable;
groves with 30 to 40 trees 25 inches d.b.h. are
ideal (<54).

Maples grown in the open — for example,
along the roadside (fig. 3) — are excellent sap
producers (6Jf, 65, 67) not only because they
have large crowns but also because they have a
large leaf area, which is necessary for both
starch and sugar production. Because of their
shorter boles, roadside trees do not make as
good saw logs as do trees that grow under
crowded conditions. Studies have been con-
ducted on the effect of fertilization {^6).

Trees in a crowded stand have smaller
crowns and therefore are not good sap produc-
ers (figs. 4 and 5) because of their reduced leaf
area.

The ideal sugar grove (figs. 6 and 7) requires
not only a planned spacing of trees but also a
good understory to protect the ground, keep it
moist, and permit growth of seedling maples to
replace mature trees that should be cut down
(fig. 8). Often these mature trees can be sold for
lumber. However, there is no such thing as a
dual-purpose maple tree — one that serves

PN-469S

Figure 1. — Grove of maple trees v/ith large crowns.which
are needed for large yields of sweet sap.

PN-4699

Figure 2. — Same grove shown in figure 1 after defoliation,
showing the branch structure of trees with large crowns.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

PN-4700

Figure 3. — Large-crowned maples, typical of roadside
trees.

PN-noi
Figure U- — Trees in a crowded stand have small crowns
and small boles. This ^rove requires thinning before it
will be a profitable source of maple sap.

equally well as a sap producer and as a source
of lumber — because the factors favoring the
growth of trees for the two purposes are not
compatible.

Consult your State extension forester, farm
forester, and county agent and work with them
to develop a management plan for your sugar
grove. Aim for 160 tapholes per acre.

PN-4881

Figure 5. — Mixed stand of crowded trees. Some trees have
long boles and small crowns. They make good saw logs
but are poor sap producers.

PN-no2
Figure 6. — An ideal spacing of maple trees, favoring the
growth of large crowns.

Sap Yields

The yield of sap in a sugar grove should be
expressed in terms of the number of tapholes
rather than the number of trees. The yield per
hole is independent of the number of holes per

MAPLE SIRUP PRODUCERS MANUAL

PN-4703

Figure 7. — This grove shows the effect of heavy grazing, a
practice not recommended since it results in reduced
sapwood production, stag-headedness, loss of reproduc-
tion, and root damage caused by soil compaction.

PN-170-1

Figure 8. — Removing overmature trees that produce sap
low in sugar content, to encourage growth of young
stock. The high cut is made to avoid some of the sap
stain and diseased wood associated with old tapholes.

tree. A mean range per taphole is from 5 to 15
gallons {95). However, a single taphole often
produces from 40 to 80 gallons of sap in a single
year — the equivalent of 3 or more quarts of
sirup.

The sugar content of the sap produced by
different trees in a grove varies considerably
(45, 110). The sap produced by the average tree
has a sugar content of 2° to 3° Brix.^ Frequently

' The density of sap and sirup is due to a mixture of
dissolved solids and not just to sugar. The physical in-
struments used to measure the density of sap and sirup
do not distinguish between the density due to sugar and
that due to other solids. The degrees Brix (° Brix) means
that the solution has the same density as a solution
containing a percentage of sugar numerically equal to the
Brix value.

trees produce sap with a sugar content of less
than 1° Brix, and occasionally a tree produces
sap with a sugar content of 9° or even 11° Brix.
A conservative estimate is that the sap from
four tapholes will yield 1 gallon of sirup. This
sap most likely would have a density of 2.2^"
Brix. Thus, 10 gallons of sap from each taphole
would be required to yield 1 gallon of sirup.

No device has been developed that will enable
a maple sap producer to determine when sap
will begin to run. However, sap will flow from
the tapholes over a period of several weeks. The
greatest yield of sap may be produced in a
single run that occurs at the beginning of the
period, at any time during the period, or at the
end of the period. In 1960 almost all the sap
crop was collected in a 24- to 48-hour period and
the Brix value of the sap was much higher than
2.2°. Many producers reported sap of 5° Brix
and higher. Because of the large volume of sap
collected in this short period, many producers
reported that their buckets overflowed. How
much was lost will never be known. This loss
would not have occurred had plastic tubing
been used for collecting and transporting the
sap.

Because of the large yield of sap in 1960 and
its high sugar content, many producers who
sold their sap to central evaporator plants re-
ceived as much as $1.90 per taphole. A yield per
taphole of 10 gallons of 5°-Brix sap having a
value of 19.5 cents per gallon gives $1.95 per
taphole. On this basis, a sugar grove with only
100 tapholes per acre would produce a gross of
$195 per acre. This may answer the question
that has often been raised as to whether the
sugar orchard should be operated to produce
sap or should be cut and sold as lumber.

The yield and sweetness of the sap produced
by a tree vary from year to year, but trees that
produce sap with a high sugar content and
trees that produce sap with a low sugar content
maintain their relative positions from year to
year {112). It is important to know the exact
sugar content of the sap produced by each tree.
Measuring the sugar content of sap is not
difficult. All that is needed is a sap hydrometer
or refractometer and a thermometer.

To make the reading, float the hydrometer in
the sap bucket or in a hydrometer can contain-
ing the sap (fig. 9). Also, obtain the temperature

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

PN-4706

Figure 9. — Measuring the density of sap C Brix) with a
precision hydrometer cahbrated in 0.1°. If the bucket
contains too little sap to provide the necessary depth
for the measurement, transfer the sap to a hydrometer
can.

of the sap so the hydrometer reading can be
corrected. (The sap should contain no ice.) Sub-
tract 0.4° Brix for temperatures of 32f to 50° F.,
0.3° Brix for temperatures of 51° to 59°, and 0.1°
Brix for temperatures of 60^ to 68".

The sap hydrometer is usually calibrated
from 0° to 10° Brix, with divisions of 0.5°. A
more accurate measurement can be obtained
by using a hydrometer with divisions of 0.1° (fig.
9).

The amount of sugar in sap is of great eco-
nomic importance. A taphole that produces 15
gallons of sap with a sugar content of 2° Brix
yields 2.5 pounds of sugar, or one-third gallon of
sirup; whereas a taphole that produces 15 gal-
lons of sap with a sugar content of only 1° Brix
yields only 1.3 pounds of sugar, or less than one-

fifth gallon of sirup. The cost of producing the
sirup from both tapholes is approximately the
same. Trees producing sap with a sugar content
of 10° Brix are especially profitable, as 15 gal-
lons of sap from 1 taphole yields nearly P/4
gallons of sirup, or more than five times as
much as the 2°-Brix sap. Trees that produce sap
low in sugar (1° Brix or less) should be culled.

Research is being conducted at the Universi-
ties of Vermont and New Hampshire, at the
Ohio Agricultural Experiment Station, and by
the U.S. Forest Service on the propagation of
maple trees from selected high-yielding trees
(20, 32, 33, 3U, U5). This research should eventu-
ally make it possible to set out maple orchards
or roadside trees that will produce sap with a
high sugar content.

Use of a germicidal pellet to prevent prema-
ture drying up of a taphole may increase sap
yields as much as 50 percent. Since the results
obtained by using the pellet are due to its
germicidal action, it will not increase the sap
crop in sugar groves where sanitary measures
are already being practiced.

Summary'

(1) Consult your State extension forester, farm
forester, and county agricultural agent and
work with them to develop a management
plan for your sugar grove. Aim for 160
tapholes per acre (160 trees 10 inches d.b.h.
or 40 trees 25 inches d.b.h.).

(2) Remove all defective, diseased, and weed
trees.

(3) Check the yield and sugar content (° Brix) of
the sap from each tree. Cull trees that yield
sap low in sugar (1° Brix).

(4) For maximum sap yields use germicidal
taphole pellets.

TAPPING THE TREE

The sap of the sugar maple, from which sirup
and sugar are made, differs in composition from
the circulatory sap of a growing tree. We know
little concerning this sap, or sweet water as it is
called in western Pennsylvania. Intensive
study of maple sap at the University of Ver-
mont (3U, 35, 57-59) should lead to a better

understanding of its nature, function, and
source, and of the factors responsible for sap
flows.

Sap will flow any time from late fall after the
trees have lost their leaves until well into the
spring, each time a period of below-freezing
weather is followed by a period of warm

MAPLE SIRUP PRODUCERS MANUAL

weather. The sap will flow from a wound in the
sapwood, whether the wound is from a cut, a
hole bored in the tree, or a broken twig.

Date of Tapping

To establish a rule of thumb that can be used
to set the date for tapping sugar maples is not a
simple matter. The date should be early enough
to assure collecting large early flows of sap (66).
Michigan and New York provide sugarmakers
with radio weather forecasts of the correct
tapping dates (22). A similar service is being set
up in other maple-producing States including
Massachusetts, Vermont, and Wisconsin. Gen-
erally, trees should not be tapped according to a
calendar date. In 1953 when this practice was
followed, many producers failed to collect the
large early flow that resulted from an unsea-
sonable, early warm spell. The danger of tap-
ping too early is now largely eliminated
through use of germicidal taphole pellets (17).
When pellets are used, trees can be tapped
several weeks ahead of the normal season.

Selecting; Trees

Selecting trees for tapping is of greatest im-
portance and can be done at any time through-
out the year.

Trees that produce sap with a density of only
1° Brix, as determined with a sap hydrometer
or refractometer, should be culled. Culling must
be done during the period of sap flow (64). If
time does not permit testing all the trees dur-
ing one sap season, test as many as possible the
first year and test the remaining trees during
succeeding years.

Trees selected for tapping should have a
minimum diameter of 10 inches at 4V2 feet from
the ground (d.b.h.) (fig. 10).

A good rule (H, 6i) for determining the num-
ber of tapholes that can safely be made in a
single tree is as follows:

Tapholes

Diameter of tree, per tree,'

inches number

Less than 10 0

10 to 14 1

15 to 19 2

20 to 24 3

25 or more 4

' Number of buckets.

PN-4706

Figure 10. — Measuring the diameter of the tree to deter-
mine the number of tapholes the tree will support.

To undertap a tree reduces the potential size
of the crop without any benefit to the tree. On
the other hand, to overtap (fig. 11) may seri-
ously damage the tree (72, 94).

Once the trees have been measured, they
should be marked so they will not have to be
remeasured each season. This can be done by
painting a numeral or a series of dots on the
tree or by using paints of different colors, such
as white for 1 taphole, yellow for 2 tapholes, etc.

Boring Tapholes

Tapholes are made by boring with either a ^/e-
inch or a ''/le-inch fast-cutting wood bit. Al-
though tapholes can be bored by hand with a
carpenter's brace (fig. 12), this method is used
only for very small operations.

For large operations, a portable motor-driven
drill not only speeds up the operation but also is
far less fatiguing. These drills are made in two
basic designs, one powered by a gasoline motor
and the other by an electric motor. In one of
the earlier models that is still popular (fig. 13),
the gasoline motor is mounted on a packboard

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

PN^707

Figiire 11. — Overlapped tree (8 buckets on a 4-bucket
tree). Note attempt to tap over large roots.

PN-170K

Figure 12. — Boring the taphole at convenient breast
height. The hole is 6 inches from that bored the pre-
vious season.

and is connected to the drill by a flexible shaft.
In other models, the drill is attached directly to
the gasoline motor, which is held in the hand.

The electric battery-powered drill (figs. 14
and 15) is newer than the gasoline-powered
drill. It is light and free from vibration and is
fast becoming popular. With either a gasoline-
or an electric-powered drill, one man can drill
holes as rapidly as a crew of two or three can
set the spouts and hang the buckets or bags, or
install the tubing.

The hole is bored into the tree, preferably at
a downward pitch of approximately 5 degrees.
The downward pitch is especially desirable if
germicidal pellets are used in the tapholes. The
hole is bored 3 inches deep or until stained
heartwood is reached. Studies at Michigan
State University {57) have shown that a taphole
3 inches deep (fig. 16) produces up to 25 percent
more sap than a taphole only 2 inches deep.

The position of the first taphole is selected
arbitrarily. The hole should be 2 or 3 feet above
the ground or, if there is snow on the ground,
as close as possible to this height. This low
position is particularly well suited to the use of
plastic tubing. The compass location of the hole
is not important. Data obtained in New York
(m) and in Michigan {16, 93, H, 96) have shovm
that the total yield is essentially the same
regardless of the compass location of the hole.
However, the warm side of the tree is favored.
Data also show that the height above ground
level has little effect on yield. The best practice
is to make the new taphole on successive years
6 to 8 inches from the previous year's taphole,
working up the tree in a spiral pattern (fig. 17).
With this procedure, the producer may tap his
tree year after year in different quadrants and
avoid striking an old taphole or dead tissue that
has been hidden by new bark, either of which
would result in a smaller flow and poorer qual-
ity sap.

When plastic tubing is used to collect sap,
there is no minimal distance at which the
taphole is located above the ground, and an
even larger area of the tree becomes available
for tapping. This permits a longer interval be-
tween periods when a repeat tap has to be
made in the same area of the tree.

MAPLE SIRUP PRODUCERS MANUAL

PN-n09

Figure 13. — A gasoline-powered portable tapping drill
with flexible shaft.

PN-4711

The power tapping drill permits drilling the
hole at different heights.

rN-niii
Figure H. — An electric battery-powered tapping drill.

The time required for new bark to grow over
a taphole depends on the health and vigor of
the tree. It is not uncommon to find the hole
nearly covered in a year (fig. 18). The hole itself
remains open, but fungus growth (109) may
occur in the new hole and stain the wood
several inches above and below the hole and an
inch or less to the side (figs. 19 and 20).

Figure 16. — The taphole is bored into the tree 3 inches
deep.

Life of a Taphole

A taphole should be usable from the time it is
bored until the buds begin to swell and the
sirup acquires an unpalatable or buddy flavor.
In the past, the taphole often dried up within 3
or 4 weeks after the hole was bored. Drying up
is caused by growth of micro-organisms in the

AGRICULTURE HANDBOOK 134, U.S. DEFT. OF AGRICULTURE

taphole rather than by air drying of the wood
tissue (13, 102, 103). When the microbial growth
has reached a count of 1 million per cubic
centimeter, sap will no longer flow from the
hole, and it is said to be dried up (J7).

In the past, a dried-up taphole was reamed to
make it flow again; it was assumed that this
procedure would remove the air-dried wood tis-
sue. However, reaming was never successful.
Research has shown that the reaming bit did
not sterilize the hole. Reaming removed only a
layer of the microbial deposit; the remaining
bacteria kept on growing. Soon, sufficient num-
bers were again produced to stop the flow of
sap. The newly developed germicidal pellets
have prevented premature drying of the tap-
hole.

PN-4714

Figure 18. — In a healthy, vigorously growing tree, the
taphole will be completely covered with new wood and
bark in 1 year.

Figure 17:

PN^ni:)
-Tapholes arranged in a spiral about the tree.

Figure 19. — A split section of a tapped maple log showing
the longitudinal stain area above and below the tap-
hole and the new growth of bark that has covered the
outside end of the hole (left).

Sanitizing Tapholes

Germicidal Pellets

A germicidal taphole pellet (fig. 21) has been
developed at Michigan State University (17). If
put into the taphole as soon as it is bored, the

MAPLE SIRUP PRODUCERS MANUAL

PN-4716

Figure 20. — Cross section of a maple log showing stained
area caused by fungus growth in old tapholes. The
stains show the exact contour of the holes including the
area entered by the screw of the bit, but do not indicate
whether the holes lie above or below the plane of the
cut. Note that the stain is confined to the width of the
taphole, which indicates that the lateral damage to the
tree is restricted to within one-half inch on each side of
the hole. But damage may extend several inches above
and below the hole, as shown in figure 19.

pellet will keep the hole essentially sterile
throughout the sap season (6 to 10 weeks) and
therefore will permit flow of sap H, 5, 6) each
time the weather is favorable. If large early
flows of sap occur, a second pellet may be
needed after 4 weeks. The active ingredient of
the pellet is paraformaldehyde which, because
of its germicidal effect and low solubility, makes
it ideally suited to this use. Each pellet must
contain a minimum of 200 milligrams of availa-
ble formaldehyde at the time it is placed in the
taphole.

The function of the pellet is to contribute
enough formaldehyde to the 1 to 5 milliliters of
sap remaining in the taphole between flow
periods to keep microbial growth to a minimum.
When the sap is flowing, the short time it is in
contact with the pellet permits only a trace of
formaldehyde (less than 5 p.p.m.) to be dis-
solved. This small amount of formaldehyde is
removed from the boiling sap while it is being
concentrated to sirup in the evaporator pan.

The very low concentration of formaldehyde in
the sap in the storage tanks will not maintain
the sap in a sterile condition {133, 13 Jf). This is
fortunate because it is sometimes desirable to
culture the sap with specific micro-organisms or
enzymes. Sap is cultured as one step in produc-
ing high- flavored maple sirup; it is also cultured
to destroy substances that are responsible for
the buddy flavor in "buddy" sap («). Other
germicides are under investigation (W, AD-

Because of the very low residue of formalde-
hyde in sirup, the U.S. Food and Drug Adminis-
tration issued in February 1962 a regulation
governing its use {130).

However, under no circumstances should
more than one paraformaldehyde pellet be
placed in a taphole, nor should formaldehyde be
added to the storage tanks. To do either might
raise the concentration of formaldehyde in sap
and contribute to a high concentration in the
sirup. This would produce sirup containing
more formaldehyde than specified in regula-
tions of the U.S. Food and Drug Administration
or of the State in which the sirup is made.

PN-4717

Figure 21. — A germicidal pellet is inserted in a taphole
immediately after the taphole has been drilled or after
it has been flushed with hypochlorite solution.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

While pellets were being developed and dur-
ing the first 2 years they were used commer-
cially (1962-63), records show that when
weather was favorable to microbial growth in
the tapholes, pellets doubled or trebled the yield
of sap. Pellets are less effective when good
sanitary practices are followed or when the
entire maple season remains cool, since micro-
bial growth is retarded under these conditions.

Elimination of the cause of premature drying
of the taphole permits tapping the tree before
the sap season with the assurance that the first
as well as the late run of sap will be obtained.
Also, the cause of diminished flows throughout
the season is eliminated. Both of these factors
increase yields of high-quality sap and decrease
the man-hours required to harvest sap (156).
Germicidal pellets are especially desirable
where plastic tubing is used to collect and
transport sap in the woods. The pellets help to
keep the pipeline (tubing) clean and sterile.

Chlorinated Solutions

In many sugar groves, chlorinated solutions
are being used to control microbial growth in
the taphole {133). The best procedure is to flush
the taphole as soon as it is drilled with a
solution consisting of 10 parts of a commercial
hypochlorite solution (containing approxi-
mately 5.25 percent of sodium hypochlorite) and
90 parts of water (fig. 22).

Often where there is a week or more between
sap runs and particularly if the nonrunning
period is warm, the tapholes should be re-
flushed with a solution of the same strength.
Where this chlorination procedure has been
practiced, a change to germicidal pellets may
not increase sap yields.

Summary'

(1) Do not tap by the calendar. Follow your
State's maple weather reports.

(2) Tap before the sap-flow season.

PN-4718

Figure 22. — Flushing the taphole with a 10-percent
commercial hypochlorite solution.

(3) Make 1 taphole in a tree 10 inches in diame-
ter and 1 additional hole for each additional
5 inches of the tree's diameter.

(4) Make the taphole with a ^'/s-inch or '/le-inch
fast-cutting (special) wood bit.

(5) Use a power tapper if the grove is large
enough to justify the expense.

(6) Bore the hole into the tree to a depth of 3
inches at a slight dov^Tiward pitch.

(7) The location of the taphole in respect to
compass position and roots is not important.

(8) Space the holes at least 6 inches apart
(circumference of tree) and in a spiral pat-
tern.

(9) Sanitize the taphole. Use 1 germicidal pellet
per taphole.

SPOUTS AND BUCKETS

Sap Spouts

The spout or spile has three important func-
tions: (1) It conveys the sap from the taphole to
a container; (2) it either connects the plastic

tubing to the taphole or serves as a support on
which to hang the sap bucket or bag; and (3) it
keeps adventitious (wild or stray) bacteria from
gaining access to the moist taphole, which
should reduce infection if plastic tubing is used.

MAPLE SIRUP PRODUCERS MANUAL

Over the years a large number of sap spouts
have been designed and used, with special fea-
tures claimed for each. The earliest spouts were
hollow reeds, often a foot or more in length.
Two reeds inserted in adjacent tapholes carried
the sap to the same container (fig. 23). There
are only a few basic differences in the design of
the various sap spouts. Some have a large
opening at the delivery end. Others have a hook
to support the bucket and a hole for attaching
the bucket cover. On others the bucket is sup-
ported directly on the spout. All commercial
spouts are satisfactory. A few spouts are shown
in figure 24.

Plastic spouts are used with plastic tubing
and they have tubulations to which the tubing
is attached.

All spouts have a tapered shoulder so that
when they are driven into position in the tap-

PN-ni9
Figure 23.— Reed sap spouts, the forerunner of metal
spouts.

Figure 2U- — Wood and metal sap spouts.

hole, they form a watertight seal with the bark
and outer sapwood but leave a free space be-
tween the sapwood and the spout. In setting
the spout (fig. 25), care must be exercised not to
split the tree at the top and bottom of the
taphole. A split results in sap leakage and often
all the sap from that hole is lost. To strike the
bark a sharp blow damages the tree and often
kills an area for several inches.

Spouts should be cleaned at the end of each
season. Metal spouts can be washed by tum-
bling in a small concrete mixer containing a
solution of a good detergent. Just before the
spouts are taken into the sugar grove at the
beginning of a sap season, they must be steri-
lized by heating them in boiling water for 15
minutes or longer. The spouts are then put in a
pail and covered with a chlorine solution con-
taining 1 cup of a commercial bleach (5.25 per-
cent of sodium hypochlorite) in 1 gallon of
water. The pail of chlorine-wetted spouts is
carried into the sugar grove. Rubber or rubber-

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

Figure 25. — Setting the sap spout.

coated canvas gloves must be worn to protect
the hands from the strong bleach.

Rain^uaixls

Heavy rains often occur during the sap sea-
son. Rainwater running down the tree picks up
dirt and leaches tannins from the bark. Both
the dirt and the tannins, if permitted to get into
the sap bucket, lower the grade of the sirup
produced. Most sap spouts are provided with
"drip tips" to deflect runoff rainwater from the
tree and prevent it from entering the bucket. In
heavy downpours, drip tips are often inade-
quate. Use of a simple, homemade rubber rain-
guard (fig. 26) prevents the heaviest runoff
rainwater from entering either a sap bucket or
bag.

To make a rainguard, cut a 2-inch square
from a thin sheet of rubber, such as an old
inner tube. With a leather punch, cut a ^/le-inch
hole in the center of the square. Slip the rain-

PN-4722

Figure 26. — Rubber rainguard prevents water from
reaching the sap bucket.

guard over the end of the spout near the tree
and set it far enough forward so that when the
spout is seated in the taphole there will be a
free space of V4 to ^/s inch between the rubber
guard and the bark of the tree.

Sap Buckets and Bags

Three types of containers have been used to
collect the sap from the spout: (1) The wooden
bucket; (2) the metal bucket; and (3) the plastic
bag.

The wooden bucket, because of its size and
the care required to keep it watertight, has
largely disappeared from use.

Zinc-coated 15-quart buckets are the most
commonly used metal buckets. Large 20-gallon
galvanized cans that eliminate daily collection
of sap are used in some "cold" sugar groves
(high altitude, northern exposure). In a cold
grove, the buckets often contain ice sap which
retards microbial growth. The minute amount
of zinc that is dissolved from the galvanized
coating by the sap tends to reduce microbial
growth, but the germicidal effect is nullified- if
the zinc coating is overlayed with a deposit

MAPLE SIRUP PRODUCERS MANUAL

from the sap (108). It can be made effective
again by carefully removing the protective film
overlaying the galvanized surface. The 20-gal-
lon containers tend to reduce microbial growth
more than do the smaller buckets (28). Lead-
coated metal (terneplate) or lead-soldered buck-
ets and buckets painted with lead paint should
not be used because the lead may be dissolved
by the sap, especially sap that has been allowed
to ferment and sour. Sirup made from this sap
may contain illegal amounts of lead. Aluminum
buckets, which are being subsidized in Canada,
tend to eliminate most objections to metal
buckets.

Every bucket should be provided with a cover
to keep out rain and falling debris. Covers are
of two general types: Those that are attached
to the spout (fig. 27) and those that are clamped
to the bucket (fig. 28).

The plastic sap bag (fig. 29), a comparatively
recent development, met with much favor, espe-
cially before the development of plastic tubing.

Some advantages of plastic bags are: (1) Be-
cause of their small bulk and weight, they
require minimum storage space, and they are
easily transported to the woods and hung. (2)
They have a self-cover that encloses the spout
when the bag is in place, and thus limits access
of micro-organisms to the open end of the spout
and to the taphole. (.3) Emptying the sap is a
one-handed operation (fig. 30). The bags need
not be removed from the spout; they can be
rotated on the spout. (4) Because they are
transparent to sunlight radiation, which is le-
thal to micro-organisms, they tend to keep the
sap sterile (76). Sterile sap contributes to the
production of high-quality sirup.

Some disadvantages of plastic bags are: (1)
They may open at seams, especially if the sap
in a filled bag freezes. (2) They are difficult to
empty when filled with ice. (3) The bag may be
too small to hold a day's run. (4) The bags are
subject to damage by rodents. (5) Washing and
rinsing the bags may be difficult.

PN-4723

Figure 27. — Sap bucket cover attached to the spout by
means of a pin. With this type of cover, the bucket must
be lifted free of the spout for emptying.

PN-1724

Figure 28. — A clamp-on cover stays fixed to the bucket
and is not easily blown off. With this type of cover, a
bucket that is attached to the spout by means of a hook
must be lifted free of the hook for emptying. However,
a bucket that hangs on the spout by means of a large
hole that will slip over the spout can be emptied by
rotating the bucket and cover on the spout.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

PN-4725

Figure 29. — Plastic sap bag: The amount of sap is easily
seen and accumulations of sap, even from short runs
over a long period of time, tend to remain sterile
because ultraviolet rays of daylight are transmitted
through the plastic. The bag has its own plastic cover.
Since the spout is completely covered, it is free from
contamination.

Summary

(1) Any commercially available spout is satis-
factory.

(2) Use only clean, sterile spouts.

(3) Drive the spout into the taphole with a firm
enough blow to seat it securely, but do not
drive it so far as to split the bark and wood.

PN-4726

Figure SO. — Emptying the plastic bag by rotating it on
the sap spout makes it a one-handed operation.

(4) Use a 2- X 2-inch rubber runoff rainguard on
the spout.

(5) Carry clean, sterile spouts wetted with a
dilute, hypochlorite solution into the sugar
grove.

(6) Do not use buckets coated with lead paint or
with temeplate.

(7) Use containers large enough to hold a nor-
mal day's run of sap.

(8) Use only clean sap buckets or bags.

(9) Use covers on all sap buckets or bags.

COLLECTING THE SAP

Collecting (gathering) sap by hand (fig. 31) is
the most expensive and laborious of all maple
sirupmaking operations and accounts for one-
third or more of the cost of sirup production.

When buckets or sap bags are used, much
time can be saved if the trees to be serviced on
both sides of a roadway bear a mark to distin-
guish them from the trees to be serviced from
an adjacent roadway. This prevents servicing
the same tree from both roadways. Different
colored paints can be used to mark the trees.

Another timesaver requires punching a sec-
ond hole in the sap bucket opposite the original
hole, and painting a stripe from that hole to the
bottom of the bucket. The buckets are hung
first from one hole (for example, with the stripe
away from the tree and plainly visible); after
they are emptied, they are hung from the
opposite hole. This makes it easy for the sap
collector to tell whether a bucket has been
emptied and keeps him from skipping full buck-
ets as well as wasting time revisiting empty

MAPLE SIRUP PRODUCERS MANUAL

Figure 31. — Collecting sap by hand is expensive. Usually
two pails are used to collect the sap from the sap bags
or buckets, and the sap is carried by hand to the
collecting tanks.

buckets. The only objection is that a bucket
with holes on both sides holds less sap than a
bucket with one hole because it hangs from the
spout at an angle.

Some producers empty the buckets by rotat-
ing (spinning) them on the spout. This requires
the use of a cover attached directly to the
bucket and a spout on which the bucket is hung
by means of a hole in the bucket. More sap may
be spilled when buckets are emptied by spin-
ning than when they are lifted free of the spout
and tree. Spillage of sap when transferring it
from bucket to gathering pail and from pail to
collecting tank may account for an appreciable
loss of the sap crop. Plastic tubing eliminates
this loss (fig. 32).

Sap must not remain in the buckets more
than a few hours before it is collected. During
short runs that produce too little sap to war-
rant collecting, the buckets must be emptied,
even though this is time consuming and expen-
sive. The sap left standing in the bucket will
ferment and spoil and will spoil other sap to
which it is added in the collecting or storage
tanks.

PN^728

PN^7

Figure 32. — No labor is required when tubing is used to
collect sap.

Collecting Tanks

Collecting tanks vary in size according to the
needs of the sugar grove. The tanks usually are
provided with a strainer, baffled to prevent loss
of sap by splashing, and a drainpipe.

The method of hauling the tank is governed
by conditions in the sugar grove. The tank can
be mounted on any of several types of carrier,
including stoneboat or skids, 2-wheel trailer,
high wheeled wagon gear, and underslung rub-
ber-tired, 2-wheel trailer (fig. 33).

High-mounted tanks should be avoided be-
cause of the labor required to lift the sap (fig.
34). Usually an additional worker is needed.

A rig of excellent design has a low-mounted
sump tank and a self-contained, power-driven
pump to lift the sap up to the large tank (figs.
35-38).

A new type of collecting tank being widely
adopted employs vacuum (suction) for filling.
Tanks to be filled by suction must be airtight
and structurally strong enough to withstand an
external pressure of 15 pounds per square inch
(1 atmosphere). Tanks larger than 300 gallons
require internal bracing. The vacuum can be
obtained by a separate pump or by connecting a
line from the manifold of the truck or tractor
engine (fig. 39). To prevent sap from entering
the engine manifold, a float check valve is
mounted on the tank and the vacuum line is
attached to this (fig. 40). The check valve is

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

/ \ w^hB^^y^^HHE^^^HuA^lBflS

PN-4729

Figure SS. — Collecting tank mounted on a truck body.
This type of assembly does not require special rigs, but
an additional man is needed to empty the pails into the
tank.

PN-n3n
Figure Si. — Additional labor is required to lift sap to a
tank mounted on a trailer.

similar to those used in milking machines that
prevent milk from entering the pump. If sap
reaches the motor, it causes serious damage.

A 1,000-gallon tank can be emptied and put
back into operation in only a few minutes. The
suction line is a 1-inch hose, which will pick up
30 gallons of sap per minute. Instead of a slow-
acting valve in the suction line, a tapered plug
is used in the pickup end of the hose. This plug
is removed just before the hose is submerged in
the sap in the tank or bucket to be emptied.

PN-4731

Figure S5. — For large operations or for collection from
roadside trees extending along several miles of roads,
the large tank trailer is desirable.

If a closed tank and an engine manifold
vacuum system is not available, a pump-and-
vacuum system can be used (2). In this novel
system, an air-cooled gasoline motor operates a
pump which, in turn, creates a vacuum in a
small tank. The sap is discharged into a conven-
tional collecting tank.

Regardless of how the vacuum in the suction
(sap pickup) line is developed, this method of
collecting sap is efficient and fast, causes a
minimum of loss due to spillage, and can be
used for collecting sap from the conventional
metal bucket, from the large 20-gaIlon con-
tainer, and from small and large storage tanks.
Whether or not the collecting tank has a vac-
uum line pickup, the tank must be as large as
roads and other conditions will permit. The
smaller the tank, the greater the number of
costly trips that must be made.

Pipelines

Metal pipelines have been used in the maple
sugar grove for 50 years or more. The early
metal pipe carried the sap over almost impassa-
ble terrain, from one sugar grove to another or
to the evaporator house (figs. 41 and 42). Metal
or wooden troughs have also been used as
"pipelines."

All these pipelines, whether metal pipe or
metal or wooden troughs, had one serious draw-

MAPLE SIRUP PRODUCERS MANUAL

Figure 36. — Sap is easily poured from buckets into a low
sump tank, from which it is pumped into the large tank.

PN^733

Figure 37. — The sap is lifted from the sump by means of a
pump. Power for the pump can be supplied by a takeoff
from the tractor or truck engine or by a small gasoline

PN-4734

Figure 38. — Vacuum lines operated by a vacuum pump
can be used to empty buckets and small containers in
the woods or at the roadside.

PN-4735

Figure 39. — The vacuum is obtained from the manifold of
the truck engine.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

Figure 40. — Float valve assembly and vacuum (suction)
line.

back; they had to be installed with great care so
that there would be no sags in the line. Sags in
pipes permitted the sap to lie there and, when a
freeze occurred, the ice formed would often
burst the pipe. Sags in troughs permitted the
sap to overflow. In addition, metal pipe was
hard to clean. Since metal pipes are opaque,
there is no simple means to determine when
they are clean. Nevertheless, the saving in time
and labor made possible by these earlier pipe-
line systems justified their use.

Suimnai*y

(1) Collecting sap by hand and hauling it is the
most expensive operation of sirupmaking.
Examine all steps and introduce laborsav-
ing methods where possible.

PN^737

Figure il. — Use of pipelines to carry sap over impassable
areas saves time. With a lateral system of dumping
stations, collecting tanks can be eliminated in some
locations. The pipeline also makes accessible some
sugar groves that would be impossible to reach by
tractor or truck.

PN^738
Figure 42.— When the sugar grove is at a higher elevation
than the evaporator house, the pipeline carries sap
from dumping stations at the edge of the sugar grove
to the evaporator house. This eliminates long and
costly hauls of sap.

(2) Wherever possible, use pipelines to trans-
port the sap.

Do not collect spoiled sap. Do not allow
small runs of sap to remain in the buckets.
Do not spill sap when pouring it into collect-
ing pails and tanks. This can account for a
10-percent loss.

(5) Use as large a collecting tank as possible to
avoid repeated hauls.

(6) Use a -pump or vacuum to fill the tank.

(7) When vacuum is used, be sure the tank is
internally braced to withstand the high ex-
ternal pressures.

(8) Keep all equipment sanitary at all times.

(3)

(4)

MAPLE SIRUP PRODUCERS MANUAL

PLASTIC TUBING

With the advent of plastic tubing, most of the
objections associated with metal pipes have
been overcome. Not only can plastic tubing be
used for collecting and transporting the sap,
but also it is cheaper to install, it has greater
flexibility and elasticity, and it is easy to keep
clean. Wide acceptance of plastic tubing by
maple producers (.38) has been a major factor in
modernizing the 300-year-old maple industry.

Use of plastic tubing has practically elimi-
nated the hard, unattractive labor of collecting
sap and has lowered the cost of sirupmaking as
much as 40 percent. No longer is it necessaiy to
construct expensive roadways through the
woods to support heavy tanks of sap and to
open these roads after heavy snows (fig. 43).
Tapping need not be delayed until the sap
season has arrived. Large crews do not have to
be hurriedly assembled to tap the trees and
hang the buckets. Instead, the lightweight plas-
tic tubing can be carried by hand through the
woods when convenient.

Some setbacks were encountered when plas-
tic tubing was first introduced. Since it had
been emphasized that sap issues from the tree
under high pressure (,39), systems for installing
the pipelines were patterned after those used
for high-pressure waterlines. It was anticipated
that enough pressure was developed by the
tree to force the sap through the pipelines, but
this was not true. The sap leaks from the
tissues of the tree under a wide range of pres-
sures, from very low (almost immeasurable) to
as much as 40 pounds per square inch. The
pressure is affected by many factors, among
which are the temperatures of the air, tree
bark, and soil. In many runs, and often
throughout most of a run, sap leaks from the
tree under very low pressure. Thus, only a
slight obstruction in a pipeline provides suffi-
cient back pressure (resistance to flow) to equal
or exceed the pressure at which the sap is being
exuded from the tree. Hence, sap flow is pre-
vented.

Causes for back pressures (obstructions) in
the line are (1) gas (vapor) locks resulting from
pockets of gas exuded from the tree along with
the sap (8) or from air pockets that result from
air that has leaked into the tubing around the

different connections, especially at the spouts
(through the vent tubes); (2) low places in the
line where pockets of sap collect, and (3) ice
plugs of frozen sap. Of these three causes,
gaslocks are most frequent and may cause
enough back pressure to support a 5-foot col-
umn of sap. However, gaslocks can be kept to a
minimum by careful installation and by provid-
ing vents to free the trapped gases or air.

The effect of ice in the pipelines is a contro-
versial subject. Many believe that by the time
the air temperature has risen sufficiently to
cause sap to flow from the tree, the tubing will
have warmed sufficiently to partly melt the ice
and allow passage of the sap. Others believe
that the elasticity of the tubing will permit the
sap to pass by the ice plug. This is unlikely. Still
others believe that tubing laid directly on the
ground, whether snow covered or not, will ab-
sorb enough latent heat from the earth to melt
the ice in the tubing before any appreciable
flow of sap occurs. Ice in tubing installed on the
ground often melts before ice in tubing sus-
pended in the air. (This can be observed when
the two systems are installed in the same sugar
grove.) There is almost complete agreement
that ice in tubing layered between two falls of
snow melts very slowly because of the insulat-
ing effect of the snow. The tubing must be
pulled up out of the snow before the ice will

PN-4739

Figure AS. — Tubing can be used for a small group of trees
in an inaccessible area or for roadside trees.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

melt and unblock the lines; this is not easy to
do when the lines are suspended.

Since maple sap is not exuded from trees at
all times under high pressure, the best method
for installing the tubing is one patterned after
that used in gravity-flow waste-disposal sys-
tems. These systems are installed with a con-
tinuous, even though slight, pitch of both the
feeder lines Qaterals) and main lines toward the
exit end. Main or trunk lines nuist be of suffi-
cient diameter so that they are never over-
loaded. Vents must be installed at all high
points to prevent gaslocks, and a vent must be
installed at each spout.

One of the outstanding features of the plastic
pipeline is the "closed" system — transparent to
daylight which minimizes microbial infections
and keeps the sap clean and free of foreign
matter (2S, 31). However, infection can and does
occur; therefore, sanitary precautions must be
observed in installing and maintaining the sys-
tem.

The immediate effects of infection are deteri-
oration and spoilage of the sap. Since infection
can be translocated by the moving sap, two or
more tapholes must not be connected in series.
This might spread infection from one taphole to
another (31 ) and prematurely stop sap flow. For
the same reason, tubing that connects the tap-
hole to either lateral or main lines must be
installed with enough elevation between the
lateral line and the taphole to drain the sap
away from the taphole freely and completely
during periods of flow and to provide sufficient
hydrostatic pressure to insure flow in the main
lines laid on level ground.

Installation of flexible plastic tubing Qateral
or main lines) suspended in the air above the
ground, free of sags between points of support
and with a continuous pitch, would be an even
greater problem than installation of iron pipe.
A suspension cable would be required. It would
be stretched from tree to tree above the tubing;
the tubing would be suspended from it and held
in a "straight" course by hangers of different
lengths. In practice, however, sags cannot be
prevented because fluctuating air tempera-
tures expand and contract the tubing and cable
and because the tubing between the hangers is
not rigid. Also, locating these lateral and main
lines so that- all tapholes will be a short but

fixed distance above the main lines U8-50)
would increase the difficulty of installation be-
cause numerous main lines and short lengths of
lateral lines would be required. This system is
ideal for small installations involving one or
only a few trees. Do not connect tapholes in
series except on individual trees. To do so may
spread microbial infection and stop flow of sap
prematurely.

In expanding this system to a large opera-
tion, the costs of initial installation, takedown,
and reassembly might be excessive. The system
does, however, eliminate the need of taphole
vents, since the short length of the dropline is
attached to main lines that are not completely
filled with sap and so will not air-lock. A
properly installed pipeline system drains itself.
If sags occur in either ground- or aerial-sup-
ported systems, pockets of sap will form. These
pockets cause buildup of back pressures, reduce
flows, are sites of microbial infection, and form
ice plugs on freezing.

Installing Tubing

There are many methods for installing plastic
tubing (68, 70). The following method (152) is
economical of materials and labor, minimizes
spread of microbial infection, and tends to elimi-
nate gaslocks and other obstructions that build
up back pressures in the lines. It provides a
simple, inexpensive, and satisfactory means for
installing, taking down, washing, sanitizing,
and reinstalling plastic tubing.

Equipment

Droplines. — Complete assemblies of 5-foot
lengths (for level land use 6- to 7-foot lengths) of
^/le-inch inside diameter (I.D.) tubing with a tee
at one end and a sap spout at the other. The
spout has a vent tube attached. Vent tubes are
U-shaped Vie-inch I.D. tubes formed with a
short piece of wire; they are from 6 to 12 inches
long and are attached to the vent tubulation of
the spout (chart 3). The U-shape tends to keep
micro-organisms out of the system.

Lateral Lines. — Lateral lines, made of ^/le-
inch I.D. tubing, connect the droplines to the
main lines. They are laid on the ground.

Main Lines. — Main lines vary in size from V2
to IV2 inches- I.D.

MAPLE SIRUP PRODUCERS MANUAL

ALUMINUM WIRE

VENT TUBE

^ ID. TUBING
16 V

Chart 5.— Vent tube and drop line assembly.

Spouts. — Spouts have two tubulations, one
for discharging the sap and the other for vent-
ing gases.

Tees and Connectors. — Plastic tees, connect-
ors, and other fittings of appropriate size are
required for connecting droplines, lateral lines,
and main lines.

Hypochlorite Solution. — A commercial bleach
containing 5 percent of sodium hypochlorite is
diluted with water at the rate of 1 gallon of
bleach to 19 gallons of water.

Germicidal Pellets. — One germicidal pellet is
required for each taphole.

Some producers find it desirable to flush all
new tubing with a stream of pure water for 10
to 15 minutes before putting it into use. This
removes any soluble material in the tubing,
including that which might produce an off-
flavor.

Droplines can be completely assembled at odd
hours before the sap-flow season. They are
assembled before they are installed in the
sugar grove and are not disassembled until
they need to be replaced. A complete dropline is
used for each taphole on each tree.

To install the lateral and main-line tubing so
that it will have the desired pitch without sags,
lay out the route it should follow before the sap
season when the ground is bare and the trees
along the route have been blazed. Painting the
trees with vertical lines (blaze marks) will show
the number of tapholes to be made per tree.
The paint can be applied in a fine stream from
a pressure paint can.

Where the slope of the ground is not too
steep, it is recommended that a tractor with
scraper blade be run over the route to level it.
A short time before the sap season, the trees
should be tapped and the tubing installed. Al-
though this can be done by one man, a three-
man team is more efficient. Not more than 25
droplines (tapholes) per lateral line should be
installed.

V/f

Li,

Beginning at a location farthest from the
storage tank and where two lateral lines con-
verge, main lines should be laid in the most
direct route to the storage tank (figs. 44-49).
Low places should be avoided if possible. The
first length of the main line should be V2-inch
LD. The size should be increased as the quan-
tity of sap entering it increases. On level
ground, a V2-inch main line will carry the sap
from 75 tapholes. Where two or more V2-inch
I.D. main lines converge, they should be at-
tached to ^/4-inch or 1-inch main lines. These, in
turn, are connected to still larger main lines as
the number of converging lines increases. In
many sugar groves only V2-inch LD. main lines
are required.

There is no absolute rule regarding size and
length of main lines except that they must be
large enough in diameter to prevent buildup of
back pressure. Pressure buildup can easily be
seen by installing 6- foot lengths of ^/is-inch vent
tubes in a vertical position at the junction
points. If sap rises in the vent tubes, the main
line is too small. The carrying capacity of a V2-
inch main line equals three to four ^/le-inch

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

lateral lines, and a ^/4-inch main line equals two
V2-inch lateral lines.

When a graded course having a uniform
downward pitch to the tank lines is impossible
because of the contour of the land, the main
lines should be suspended from overhead guy
wires or cables. Suspended installation is espe-
cially suited for long runs of rnain lines over
very rough, rocky land, gullies, ravines, and
valleys. A properly installed main line will
drain itself.

Tapping nnd Droplines

If trees are tapped and droplines are installed
by a three-man team, the first man locates the
position for the taphole and bores the hole. He
sanitizes the bored hole either by syringing it
with the hypochlorite solution or by inserting a
germicidal pellet. The second man carries the
dropline assembly and attaches it to each tap-
hole by driving the spout firmly into the tap-
hole. The third man furnishes droplines, hy-
pochlorite solution, and other supplies to the
first two men.

PN-4-41
unction of several main lines with surge
tank and vent.

PN-4-40

Figure H- — Main line used to transport sap across
inaccessible area.

Figure J,6. — Main lines transport sap to storage tank at
the evaporator house.

MAPLE SIRUP PRODUCERS MANUAL

PN-4743

Figure U7. — Main line to roadside tank for pickup.

Lateral Lines

Coils of ^/le-inch LD. tubing are taken to the Figure j,><.
starting point of installation in the sugar grove,
usually the storage tank at the roadside or at
the evaporator house. The laterals are laid out
and connected by a second three-man team.

The leadman of the team carries the coil of
tubing. One of the other men holds the end of
the tubing. The leadman lays the tubing to the
first tree tapped. The line should be kept free of
loops and should lie flat on the gi-ound. The
tubing is gently pulled to straighten it out and
the desired length is then cut from the coil. One
of the other two men holds the cut end of the
coiled tubing, and the leadman advances to the
second tree, laying out the tubing as he goes.
The second and third men alternate in the
following tasks: Holding the tubing while it is
being laid out; disinfecting the ends of the
tubing, tees, and connectors; and connecting
the laterals to the tees of the droplines. Where
there are multiple drops (tapholes) on one tree,
they are connected with 1-foot pieces of */ie-inch
LD. tubing.

Laying tubing in shaded areas should be
avoided. All connections and droplines to later- Figure 1,9.

f'N-n4j
-Droplines are installed before ground lines
are laid out.

PN-4746

-The leadman carries the coil of tubing.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

als should be on the southern side of the tree to
favor early thawing of any ice formed in the
joints (figs. 50 and 51).

After the tubing has been installed, the en-
tire system must be checked to insure' that all
connections have been properly made. Inspec-
tion tours should be repeated throughout the
sap-flow season to check for le^ks and sepa-
rated joints. Inspections are necessary if the
tubing was installed over deep snow that melts
during the sap season or if new fallg of snow
cover the tubing.

Takinjj Down Tubing

Tubing must be taken down not later than 1
week after the last run, or after the trees begin
to bud. To delay permits growth of micro-orga-
nisms and makes washing and sanitizing more
difficult. During the sap-flow season, tempera-
tures are usually cool enough so that the rate
of germination of any micro-organisms in the
tubing is slower than their death rate caused
by the transmission of ultraviolet radiation of
sunlight through the tubing. But, as the season
progresses beyond the budding period, the

PN-47 4(1

Figure 50. — Droplines are connected to laterals.

PN-4747

Figure 51. — Several laterals are joined to the main line
with tees or the newly developed collector.

warmer weather causes the growth rate to
greatly exceed the death rate of the organisms,
and abundant growth occurs. Therefore, taking
the tubing down immediately after the end of
the season makes the cleaning operation easier.

The process for taking the tubing down is
merely a reversal of that described for its in-
stallation. Like the installation, this process can
be a one-man operation; but it is more efficient
when done by two 2-man teams.

The leadman of the first team at each tapped
tree disconnects the droplines from the laterals
and the foot-long connectors, which he collects.
The second man pulls the spouts from the tree
and collects the dropline assembly. Disconnect-
ing lateral lines, short connectors, and drop-
lines, and tying tubing bundles are shown in
figures 52-56.

MAPLE SIRUP PRODUCERS MANUAL

When 25 droplines have been collected, they
are tied into bundles, with the tee ends flush.
Since all droplines are alike, no labeling is
needed.

Figure 52.— Taking down droplines.

Figure 53. — Taking up lateral lines.

Figure .54.— Tying and labeling bundles of lateral lines.

The second team collects, bundles, and tags
the disconnected lateral lines. The leadman
collects the tubing. Beginning at the first
tapped tree, he picks up the end of the tubing
that extends from the main line or storage tank
and pulls the tube to the second tree. There he
picks up the end of the tube e.xtending between
the first two trees and places the end flush with
the end of the first tube. Then he pulls the two
lengths of tubing to the third tree and repeats
the process until a handful of tubing (20 to 25
pieces) has been collected. Smaller lots may be
obtained from an isolated section of the sugar
grove.

When a handful of tubing has been collected,
it is left at the tree where the last piece was
collected. Another member of the team ties the
flush ends together into a bundle and attaches
a label showing the general area of the sugar
grove where it was installed. The bundle of
tubing is then tied into a coil approximately 2
feet in diameter for easy handling.

This system of installing and dismantling the
tubing not only is simple but makes washing
and sanitizing of the tubing easy.

\^a!*liiii<; and .Saiiilizin^ Tiil»iii<£

At the end of the maple season most of the
interior of the tubing is either wet or moist with
sap. With the warmer weather at that time.

AGRICULTURE HANDBOOK 134. U.S. DEPT. OF AGRICULTURE

Figure 55.

PN-47.'->l

Coiling lateral lines for ease of handling.

Figure 56. — Load of tubing to be taken to evaporator
house for cleaning and storage.

temperatures are favorable to microbial prrowth
(yeasts, molds, and bacteria). However, if the
sap in the tubing: were sterile, either because of
excellent sanitary practices or because of the
sterilizing effect of sunlight, no subsequent
gi'owth would occur. But this seldom, if ever,
happens. Excessive microbial growth usually
occurs, especially if higher temperatures follow

takedown of the tubing. Once gi'owth occurs, it
becomes increasingly difficult to clean the tub-
ing. Therefore, the tubing should be washed
within a few hours after its takedown, and if
that is not possible, within 1 or 2 days. Tubing
in which microbial gi'owth is excessive must be
cleaned by more elaborate methods.

Etiiiifniiriil

The following equipment is requii'ed for
washing the tubing:

(1) A tank to hold the hypochlorite solution.
This can be a 55-gallon drum or a stock-water-
ing tank of approximately 200-gallon capacity.

(2) A gear-pump that will deliver at least 50
gallons per hour at 10 to 15 pounds' pressure. A
bypass arrangement on the pump provides flex-
ibility of operation. The pump is attached to the
drain valve of the tank and is equipped with a
15-foot length of hose provided with a tapered
nozzle.

(3) Wash or sanitizing solntioti consisting of a
10-percent solution of a commercial liquid
bleach (which contains approximately 5 percent
of sodium hypochlorite); 20 gallons should be
used with 180 gallons of water.

ii) Rubber gloves to protect the hands against
the caustic action of the sanitizing solution.

MAPLE SIRUP PRODUCERS MANUAL

W ashing l.<itfr<ils

Rubber gloves are worn. A coil of the tubing
is submerged in the tank of hypochlorite solu-
tion (fig. 57). The drain valve connecting the
tank and pump is opened, and the pump is
started. The stream delivered from the hose
nozzle is adjusted by means of the pump bypass
valve. The bundle of tubing is picked up by the
flush ends. The nozzle is inserted into one of
the tubes until the tube is completely filled with
the wash solution (fig. 58). Filling a tube com-
pletely usually requires less than a minute.
When air bubbles no longer emerge from the
discharge end, the tube is completely filled. As
each tube is flushed and filled with hypochlorite
solution, it is released so that only the un-
washed tubes are held. When all tubes in a
bundle have been flushed and filled with clean-

PN-n54

Figure 5S. — After soaking, the tied end of the bundle is
held and each tube is washed separately.

ing solution, the coil is allowed to sink to the
bottom of the tank and another coil of tubing is
placed in the tank. Then the process of flushing
and filling each tube of the new coil is repeated.
This is continued until the tank is filled with
tubing.

CAUTION

Because of the eaiistie action of the
hypochlorite solution, ruhher gloves must
Im' Moi-n (luring the Mashing operation.

PN-4753

Figure 57. — Coils of lateral lines are submerged in hy-
pochlorite solution, and all the ties are cut except those

at the end of the bundle.

The tubing is soaked for 2 hours; then each
tube is flushed again, beginning with those in
the first coil put in the tank. As soon as all the
tubes in a bundle have been washed, the
strings holding the bundle in the coil are cut
but not the string holding the flush ends of the
tubes. Then, the bundle, held by the flush ends,
is pulled slowly from the tank (fig. 59). As the
coil unwinds, the solution in the tube drains
back into the tank.

The bundle of tubing is then pulled to a slope
or laid over the roof of a building to drain (fig.
60). Thus, the hypochlorite solution is drained
from the tubing but not washed out.

After 10 to 15 thousand feet of tubing has
been washed, the tank should be drained and
refilled with fresh hypochlorite solution.

After the bundles have drained for about 2
weeks, they are taken down and coiled (fig. 61).

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

Figure 59. — The wash solution drains back into the tank as the tubing is slowly

withdrawn.

PN-47r>H

Figure 60. — The tubes are laid out on an incline or over a
roof to drain. Here, 12 miles of tubing is being dried.

Extremely dirty tubing or tubing; with an ex-
cessive amount of microbial growth should be
thoroughly cleaned (Hi ).

For storage, several bundles of tubing from
the same area of the sugar grove may be
wound and tied in the same bundle. The coils of

PN^757

Figure 61. — The tubing is coiled on a homemade reel, tied
into bundles for storage.

tubing are stored in a clean, dark, cool place
that is free of rodents. Large metal drums or
tanks with 'Vinch-mesh hardware cloth covers
make ideal, rodent-free storage containers.

A bundle of droplines held by both ends is
lowered slowly and perpendicularly, tee end

MAPLE SIRUP PRODUCERS MANUAL

first, into the tank of hypochlorite solution to
displace the air and to completely fill the tubing
and fittinfa:s (tees, sjwuts, and vent) with solu-
tion (fig. 62). Without releasing the bundle, it is
lifted out of the solution and held in a vertical
position for a few moments to drain. The ends
are then reversed and the bundle is again
lowered into the solution. After the second
filling the bundle of droplines is left in the tank
to soak for 2 hours. After the soaking period, it
is lifted free of the solution and held in a
vertical position for a few seconds to permit
most of the hypochlorite solution to drain back
into the tank. The bundle is then hung by the
cord ties at the spout end for 2 weeks (fig. 63).
After draining, the bundle of droplines is taken

down and stored in the same manner as the
lateral lines.

Washitif! Main Lines

The coils of main lines are washed, drained,
and stored in exactly the same manner as the
lateral lines. A larger nozzle is used to fill and
flush the tubing with the hypochlorite solution.

Reinstalling Tubing;

The operation of reinstalling the tubing in
the sugar grove proves the merit of this system.
This operation is carried out in practically the
same manner as that of the initial installation.

Main Lines

The cut, clean, large-diameter tubes are laid
out in the sugar grove in the same manner as
in the initial installation.

Droplines and Lateral Lines

Two 3-man teams are used to reinstall drop-
lines and lateral lines. The first team drills and
sanitizes the tapholes and inserts the germici-
dal pellets, and installs the dropline assemblies
that have been kept intact in convenient bun-
dles.

PN-47SK

Figure 62. — A bundle uf dicjijlines is lowered slowly and
jierpendicularly into the wash solution.

PN-n59

Figure 63. — The drained droplines are hung in a vertical
position to dry.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

The second team lays out and connects the
lateral and main lines. The coiled bundles of
lines are sorted and the one with the label for
the sugar grove area where the work is to begin
is selected. The coil is cut apart, and the lead-
man of the team, holding a bundle by the tied
flush ends, pulls it to the first tapped tree,
following- the blaze marks of the preceding year.
Since each bundle contains tubing of different
lengths, the second man (who is at the starting
point at that time) selects the tube that
matches the distance from the starting point to
the first tree and pulls it from the bundle. Both
men now advance. The leadman proceeds to the
second tree and the second man to the first
tree, where he again selects a length of tubing
that matches the distance between the two
trees. He connects the lateral lines with the
tees of the droplines. This procedure is repeated
until the entire grove has been reassembled
with the droplines and lateral lines.

siimniarv'

Plastic tubing can be used for the full opera-
tion of sap collection and transportation or it
can be used to perform parts of these opera-
tions.

(1) Install plastic tubing as a drainage system
with proper vents and adequate size tubing
so as not to restrict sap flow in tubes.

(2) Do not connect tapholes in series, except
possibly those on individual trees.

(3) Lay the tubing on the ground or suspend it.
Avoid any sags in the lines, and vent these
whenever they occur.

Installiufi Tubinn

(1) Tubing is ground-supported lateral and
main lines.

(2) Each taphole is connected to the lateral
line by a dropline consisting of a spout,
vent, and 5-foot length of ^/le-inch tubing,
and a tee connector, preassembled.

(3) Lateral lines are ^/le-inch tubing cut to fit
between different trees.

(4) Make connections of lateral lines and drop-
lines on warm side of trees.

(5) Lay the lateral lines along a route of con-
stant pitch free of sags, previously laid out.

(6) A 3-man team lays out the lateral line
most efficiently.

(7) The number of droplines connected to one
^/i6-inch lateral line will depend on (a) the
flow of sap per taphole and (b) the pitch of
the lateral line. Do not connect more than
25 tapholes per lateral line.

(8) A V2-inch main line will cari-y sap from 75
tapholes (3 laterals).

(9) Increase the size of the main lines so that
they are never overloaded. Failure to do so
will cause back pressure and loss of sap.

(10) Periodic inspection of the tubing is re-
quired for leaks.

Taking Doivn Tubing

(1) Take the tubing down as soon as possible —
never later than 1 week after last run.

(2) Remove all droplines intact, and tie in a
bundle.

(3) Keep 1-foot connectors separate.

(4) Collect lateral lines, keeping the lead ends
flush in the hand-held bundle.

(5) Coil and tie for ease of handling.

(6) Label the bundle at flush ends for the area
of woods where installed.

Washing and Sanitizing

(1) Wash all tubing in a 5-percent hypochlorite
(bleach) solution.

(2) Submerge and soak all tubing and fittings
in hypochlorite solution for at least 2 hours.

(3) Flush out all tubing as per preceding in-
structions.

(4) Keep flush ends of tubing tied in bundle at
all times.

(5) Open coiled tubing after washing.

(6) Lay tubing on incline to drain.

(7) Hang droplines in vertical position.

(8) Recoil droplines and mains for storage.

(9) Store in dark, dry, rodent-free area.

Rfinstalling Tubing

(1) Follow the same procedure as initial instal-
lation:

(a) Install droplines.

(b) Connect droplines.

(d) Connect lateral lines to main lines.

(2) Lateral lines are laid out according to the
scheme outlined in text.

MAPLE SIRUP PRODUCERS MANUAL

VACUUM SYSTEMS

The most recent development in collecting
sap has been the use of vacuum to increase
taphole flow and facilitate sap transportation in
plastic tubing and pipeline systems (7, 1,7, 105).
To utilize vacuum, an unvented or closed tub-
ing system must be used. The vacuum may be
created by the flow^ of the sap through the
tubing due to gravity (natural vacuum) or by
the use of a pump (pumped vacuum). The best
vacuum system will depend on the individual
characteristics of terrain and tree stand for
each sugar bush. Where an adequate natural
slope exists, natural vacuum can produce siza-
ble increases in the yield of sap. The details of
installing such a system are described by Mor-
row (73). Gains in sap production are generally
directly proportional to the amount of vacuum
in the system, whether produced by natural
flow or by a pump. As there are many areas in
the North American maple belt where the slope

of the land is not sufficient for an effective
natural vacuum, artificial vacuum systems
have been developed. Several agencies have
done research on pumping systems (19, 106). A
review of the different types of units that can
be assembled was presented at the Eighth
Conference on Maple Products (UU).

It has been well substantiated that vacuum
markedly increases sap yield. However, the re-
ports on the use of vacuum emphasize the
relative complexity of the equipment systems.
Those wishing to incorporate vacuum, either
natural or pumped, into their sap collection
should obtain assistance from someone thor-
oughly experienced with these systems. County
agricultural agents in the maple sirup-produc-
ing areas can recommend sources of expert
advice on using vacuum and on installing the
equipment needed in a sap-collection system.

STORAGE TANKS

Storage tanks serve the dual purpose of pro-
viding supplies of sap to the evaporator and of
storing sap until it can be processed or hauled
to an evaporator plant. Tanks supplying either
a farm evaporator or a central evaporator plant
must hold enough sap for at least 2 days'
operation. Tanks used as pickup stations must
be large enough to hold the maximum daily sap
production of the sugar grove or of the area
they serve. Pickup tanks used to haul sap from
the sugar grove or to deliver sap to the evapo-
rator house must be as large as possible to
reduce the cost of haulage.

Wherever possible, locate the tanks so that
they can be filled and emptied by gravity (figs.
64 and 65). When this is not possible, motorized
pumps (electric or gas engine) can be used.

The tanks should be located in a cool place
(fig. 66) and not inside the warm evaporator
house, since warm sap favors microbial gi'owth.
The tanks should be covered to keep out foreign
material, and the cover should be clear plastic
or some other transparent material that will
transmit the short ultraviolet rays of daylight
(100). This type of installation is especially
suited for roadside storage.

If abovegTound tanks are not emptied fre-
quently, they should be insulated to prevent
the stored sap from freezing. Underground
tanks with opaque covers, although less likely
to freeze, are difficult to irradiate with ultravi-
olet light (fig. 67). When the covers of under-
ground tanks are not transparent to the ultra-
violet irradiation, germicidal lamps must be
installed at the top of the tanks to illuminate
the entire surface of the sap. Underground
tanks will usually keep the sap at a more even
(and perhaps at a slightly lower) temperature
than will aboveground tanks. But since many
of the bacteria that infect sap gi-ow well at low
temperatures, underground storage will not
prevent microbial fermentation and spoilage of
sap. Even lowering the temperature of the sap
by adding ice will not prevent this.

Large storage tanks such as those at the
evaporator house should also be provided with
germicidal, ultraviolet lamps to prevent micro-
bial gi-ovd,h. These lamps should be mounted at
the top of the tanks above the liquid level and
arranged so that they will illuminate as much
of the surface of sap as jwssible. Directions for
making an inexpensive ultraviolet-irradiation

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

}'N-4760

Figure 61,. — The plastic-covered roadside tank should be large enough to hold a maximum daily run and should be
located so as to permit gravity filling of the collecting tank.

Figure 65. — This receiving tank is mounted at the road-
side. Sap is pumped from it to the evaporator storage
tank.

Figure 66.— This small evaporator storage tank, mounted
in the shade, is e.xposed to daylight and covered with
transparent plastic.

MAPLE SIRUP PRODUCERS MANUAL

unit for pasteurizing flowing sap are available
(AS).

CAUTION

€

are

mil

St be taken nevt

»r to exp

ose

the

eyes

ultraviolet

lamps.

Lamps

must

turn

e<l

off when

worke

rs are

around

the

tanks.

Tanks must have easy access for cleaning
and repair. Workers must be extremely careful
when working in tanks that have only a man-
hole opening, so as to be sure they do not
exhaust the oxygen (ft-esh air) supply and suffo-
cate.

Metal or glass-lined tanks such as surplus
milk tanks are ideal, since their walls are non-
porous and easy to clean.

The walls and floor of masonry tanks should
be smooth and treated with a water-insoluble
coating to prevent places for microbes to lodge.
This surface-treating material must be one that
is approved by the U.S. Food and Drug Admin-
istration as safe for being in contact with food.

The tanks should be washed with a detergent
after each run of sap and the detergent should
be completely removed from the tanks by using
at least three separate fresh-water rinses.

There must be some indicating device inside
the evaporator house to show the level of sap in
the tank. This device may be simple sight glass
(a perpendicular glass tube connected to the
feed line of the evaporator), or it can be a float-
and-weight type, where a string attached to a
float in the tank is carried into the house, and a
weighted object is raised and lowered by means
of guides and pulleys as the level of the sap
varies.

Figure 67. — A large underground concrete storage tank of
silo-type construction.

If the feed line from the tank to the house is
aboveground, it too must be well insulated.
Numerous cases have been reported when the
sap line, even when in operation, has frozen
and shut off the supply of sap, with the result
that the pans were burned.

Suinmarv'

(1) Construct tanks with smooth, easy-to-clean
walls.

(2) Locate tanks in a cool place — never inside a
warm evaporator house.

(3) Cover tanks with clear plastic to utilize the
sterilizing action of sunlight.

(4) Provide sterile lamps for large tanks with
opaque covers.

(5) Provide an indicating device in the evapora-
tor house to show level of liquid in tank.

(6) Keep tanks clean and sterile.

EVAPORATOR HOUSE ON THE SAP-PRODUCING FARM

Location

Originally, most evaporator houses were lo-
cated near the center of the sugar grove to
shorten the distance the sap had to be hauled
(fig. 68). With the use of pipelines and large
collecting tanks, many producers today find it
more profitable to locate the evaporator house

near the other farm buildings and close to a
traveled road (fig. 69). This offers many advan-
tages: (1) Water and electric power are availa-
ble; (2) laborious and time-consuming travel to
and from the evaporator house is eliminated; (3)
full family participation is encouraged; and (4)
the evaix)rator house is accessible to visitors
and potential customers.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

Funotiun

The evaporator house, or sugar house as it is
often called, like the evaporator, has developed
without engineering design. In the early days
of the iron kettle, little thought was given to
any form of shelter. At first only a lean-to type
of shed was used to protect both the sirup-
maker and the boiling sap Ifrom inclement
weather, which so often occurs during the sirup
season. The shed introduced a new problem —
how to get rid of the steam from the boiling sap.
This problem was solved by completely enclos-
ing the evaporator and installing ventilators at
the top. These crude shelters were the forerun-
ners of today's evaporator houses.

Since the evaporator house is used only from
4 to 6 weeks each year, its cost must be kept
low; otherwise, the interest on the capital in-
vestment is out of proportion to its use. The site
should permit use of ramps for filling the stor-
age tank by gravity (figs. 70 and 71). The house
should be constructed so that it not only per-
mits sanitary handling of sap and sirup but also
provides a place to process and package the
sirup, to make confections, and to sell maple
products.

Requirements

The evaporator house need not be elaborate.
It should be large enough to allow plenty of free

Ife-^-'*

Figure 68. — Evaporator house located in center of sugar
grove. Without a covered evaporator, steam completely
fills the evaporator house. This is unfavorable for sani-
tary conditions.

PN-4765

Figure 69. — The trend is to locate the evaporator house
near the other farm building-s and on an improved road.

space (at least 4 feet) on all sides of the evapo-
rator, and it should be set on a foundation that
extends below the frostline. The house should
be tightly constructed and should have provi-
sions for venting the steam. If open hoods are
used, there should be intakes to supply air for
the fire and to replace air that is exhausted
with the steain. Provision should also be made
for easy access to the fuel supply and sap
storage tanks.

I)esig;n

Chart 4 shows a suggested plan for an evapo-
rator house with a wing in which the sirup can
be processed and maple products can be made.
The house itself is designed to contain only the
evaporator and a workbench along one wall.
The width (16 feet) allows an aisle space of 5
feet on each side of an evaporator 6 feet wide
to provide easy access to all parts of the evapo-
rator.

.Strain Nontilalion

In concentrating sap to sirup, vast quantities
of steam are produced. Without proper means

MAPLE SIRUP PRODUCERS MANUAL

PN-4766

Figure 70.— When possible, select the evaporator house
site so that the natural elevation will permit building a
ramp, and sap can be delivered by gravity from the
hauling tank to the storage tank and from the storage
tank to the evaporator.

for removing: it, the steam fills the evaporator
house and, on cold days with high humidity, the
inside of the house becomes dripping- wet. In a
steam-filled evaporator house, the sanitaiy dry
conditions desired in a food-processing plant ai'e
impossible (fig. 72). Instead, the wet building
favors microbial gi-owth.

The earliest method of removing steam and
the least effective was to cut a hole in the

Figure 7;.— When the site is level, the sap can be pumped
to storage tanks mounted on elevated frames; it will
then flow by gravity to the evaporator.

center of the roof directly above the evaporator.
The hole was the same size as the evaporator.
The cover for this hole was fastened to the roof
with hinges on the side of the hole parallel to
and opposite the ridge of the roof These hinged
roof sections or louvers were raised or lowered
by a rope and pulley. The rope was wound on a
windlass mounted on the wall of the house.

Tin' Opi'ii llooil

The next method for removing steam from
evaporators was the open hood (fig. 73). In this

.CHIMNEY

^ STEAM VENT STACK

WORKBENCH

SPACE FOR

SIRUP

FILTER

SUGAR KITCHEN
I2'-0"X 15'- 8"

REHEATING STOVE
PACKAGING SPACE

EVAPORATOR HOUSE APPROX. I6'-0"X 20'-0"
METAL-LINED HOOD

SAP STORAGE TANK
WITH GERMICIDAL
LAMP

EVAPORATOR

-FUEL STORAGE
-xTANK (UNDERGROUND)

ChaH 4.— Suggested plan of an evaporator house with "L" to provide space for filtering and packaging sirup and making

maple confections.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

PN_176R

Figure 72. — Evaporator house with opening in the roof
for venting the steam results in a steam-filled building.

method, four walls extending from the rectan-
gular roof opening to within 6 feet of the floor
are constructed to serve as a chimney for the
steam. The walls are sloped so that the lower
edge projects 1 foot or more beyond the four
sides of the evaporator. The efficiency of the
hood is increased by attaching a strip of light-
weight canvas 1 to 3 feet wide to the lower edge
of the hood. A small gutter V2-inch deep is
attached to the lower inside edge of the hood to
collect water that condenses in it. Since the
hood has nothing to support, it can be made of
lightweight, noncorroding material such as
sheet aluminum. The supporting frame can be
made of lightweight lumber, and covered with

aluminum on the inside so that only the metal
is exposed to the steam.

This type of hood will keep the evaporator
house free of steam, but it has many draw-
backs. Being open, it requires 10 volumes of air
for each volume of steam removed. Thus, large
volumes of air must be drawn into the evapora-
tor house, which makes the house cold and
drafty. Also, the efficiency of the hood is af-
fected by wind and by barometric pressure.
Although the open hood is found in many older
evaporator houses, it is not recommended be-
cause it results in unfavorable sanitaiy condi-
tions.

Tlip Covered Evaporator

A simple, effective method for removing
steam from evaporators is a close-fitting, but
not airtight, cover from which the steam is
conducted to the outside of the house through a
duct or stack (fig. 74). The cover rests on the
evaporator. This method uses the same princi-
ple as that used to vent the steam out the spout
of a boiling teakettle (fig. 75). The method has
none of the objectional features associated with
earlier methods. It does not require an exhaust
fan and it does not raise the boiling point of the
sirup, since there is no measurable increase in
pressure within the steam-venting system.

The cover is made of lightweight, noncorrod-
ing metal such as sheet aluminum and has a

PN-4769

Figure 73. — A canopy-type hood removes steam more
efficiently than do louvers. However, large volumes of
air are require<i to sweep the steam into and up
through the hood and the result is a cold, drafty
building.

Figure 7U. — The tight-cover steam-venting system with
steam stack provides a simple, highly efficient means
for removing steam. This results in a steam- and draft-
free evaporator house.

MAPLE SIRUP PRODUCERS MANUAL

PN-mi
Figure 75.— The hot steam causes a natural draft and
does not require air intake ports.

light wooden frame of gable design made from
1- X 4-inch pitch-free lumber (spruce or bass-
wood). The aluminum sheets are cut to size and
are attached by aluminum nails to the inside of
the wooden frame, completely covering the
wood so that it is not exposed to the steam.
Galvanized iron should not be used, since the
acidic gases in the steam will quickly corrode
and dissolve the zinc coating.

A satisfactory pitch of the gabled cover is 6
inches to the foot, or 30°. The walls of the cover
should be 6 to 8 inches high to provide adequate
headspace for the free boiling sap. A trap door
should be placed over the flue (back) pan to
permit inspection and skimming. However, the
tight cover has practically eliminated the need
for skimming. This is no doubt due to the
absence of air ft-om the steam-filled area above
the boiling sap.

The pipes for the stack or steam vent should
be made of the same lightweight metal, and
they can be fabricated in any sheet-metal shop.
The stack should be placed over the flue or sap
pan, because that is where inost of the steam is
generated. The stack should be fastened at its
base to the evaporator cover. It should be long

enough to extend up to and through a hole in
the roof of the building to 1 foot above the ridge
of the roof.

The opening in the roof should be 1 inch
larger in diameter than the stack, so that the
stack can be moved freely. The diameter of the
stack is not critical; however, it must be large
enough for the steam to escape readily. Stacks
of different diameters are required for different
size covers, as follows:

Size of cc

tvered

evaporator

Diameter of
stack '

Width (Jeet) Length {feet)

Inches

4
4

4 I

5 (

'' )

10 \

4
6

10 )

10 \

5 14 I ig

5 20 I

' For covers over flue pans use next larger diameter;
for covers over sirup pans use next smaller diameter.

For evaporators with two or three sections, it
is easier to construct separate covers with indi-
vidual steam stacks for each section.

To remove the cover, hoist it and the at-
tached steam stack vertically — push the stack
up through the roof opening — by means of a
I'ope attached to eye bolts at each end of the
ridge pole of the cover. Pass the rope through
pulleys located overhead and then down to a
windlass mounted at a convenient height on
the sidewall of the evaporator house.

I^ocation of" K\a|><n-ator

The evaporator should be located directly
under the ridge of the roof and centered under
the hood (if an open hood is used). The founda"
tion for the evaporator arch should be made of

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

masonry or cast iron. The masonry arch or the
base of the cast iron arch should extend below
the frostline and sufficiently high above the
floor level so that the height of the evaporator
permits the sap to flow by gi-avity from the
pans to the filter tank and then from the filter
tank to the finishing pan. Setting the evapora-
tor high also makes it easier ^o fire when the
fuel is wood, and brings the thermometer (for
checking the boiling point of the sirup) to eye
level for ease of reading.

If the sirup is only partly finished in the
evaporator and evaporation is completed in a
finishing pan, the finishing pan should be
mounted adjacent to the evaporator.

Air Supply

When the evaporator is in operation, great
quantities of outside air are required for com-
bustion of the fuel. For example, 150 cubic feet
of air per minute is required to burn seasoned
hard maple at the rate of one-fourth cord per
hour. If the steam is removed through an open
hood, an additional 10 cubic feet of air per
minute per square foot of evaporator will be
required. For example, an evaporator 4 feet
wide and 12 feet long requires 480 cubic feet of
air per minute to remove the steam through a
ventilator.

If this air is supplied through an open door or
window, the evaporator house will be very cold
and drafty. A more desirable method is to
deliver air where it is needed. Ducts along both
sides of the evaporator will supply the hood
ventilation and the combustion air. These ducts
should be 8 inches wide and open at the top and
at the ends toward the firebox. They should run
the entire length of the evaporator. The air
coming in through these ducts tends to keep
the steam under the hood. If the evaporator is
covered and has a steam vent pipe, the ducts
will need to supply air only for combustion.

Siriip-Proressinjj Room

If the evaporator house is a single room, it
must have space for filtering the sirup and for
canning it. It is better to process the sirup in a
second room built as an "L" to the evaporator
room (chart 4). This arrangement does not add
appreciably to the cost of construction and the

sirup can be processed under better working
and sanitai-y conditions.

The processing room houses such operations
as filtering, heating, and packaging the sirup,
and making maple confections. The equipment
consists of a filter rack, a stove for boiling the
sirup (preferably heated with gas), a maple-
cream beater, and sugar stirrers.

There should be a sink for dish washing, a
hot water heater, and a trough with cold run-
ning water in which sirup that has been cooked
for making maple cream can be cooled rapidly.
Storage space should be provided for cooking
utensils and containers.

If the evaporator house is to serve as a
salesroom, space should be provided for display-
ing the products attractively and for storing
the products.

Fuel Storagje

When wood is used for fuel, sheltered storage
must be provided in a convenient location. This
storage space holds enough wood for a run of
sap. The supply is replenished from a larger
storage shed. In some large operations, the
wood is stored in a separate building and is
transported to the evaporator house in a truck
mounted on rails (fig. 76). An overhead tram-
way can also be used. By installing the tracks
with a slight downgrade toward the evaporator,
the heavy loads of wood can be moved by
gravity.

Figure 76. — Wood for fuel is conveniently

separate shed. The wood is moved in a flanged-wheel
truck that runs on rails to a point adjacent to the
evaporator. If the storage shed is at a slightly higher
elevation.'the loaded truck can be moved by gravity.

MAPLE SIRUP PRODUCERS MANUAL

Fuel oil storage tanks must be large enough
to hold enough oil for at least 1 day's operation.
Larger tanks may lower delivery costs. The
tanks must be installed to meet local building
codes.

Suinniaiy

(1) If possible, locate the evaporator house on
the main road close to the other farm
buildings.

(2) Build it large enough to provide at least 4
feet of free space on all sides of the evapo-
rator.

(3) Construct it so that it can be kept clean.

(4) Provide a w^orkbench along one w^all.

(5) Provide the evaporator with a cover and
steam vent pipe.

(6) Elevate the evaporator arch on a founda-
tion that extends into the ground below
the frostline.

(7) Make the floor of concrete or other easily
cleaned surface.

(8) Provide ducts in the house for intake of
outside air.

(9) Set the evaporator high enough above
ground to raise the pans a minimum of 4
feet above the floor.

(10) If possible, provide a separate but adjoin-
ing room for processing the sirup and mak-
ing other maple products.

(11) If possible, equip the house with running
water, electricity, and gas fuel supply.

(12) Provide adequate storage for dry wood or
oil.

(13) If wood is used for fuel, provide means for
transporting the wood to the evaporator.

(14) Locate the sap storage tanks outside the
building.

(15) Cover the tank with material (plastic)
transparent to the low ultraviolet radia-
tion of daylight.

(16) If the tank is enclosed, illuminate the sap
with germicidal lamps.

THE EVAPORATOR AND ITS FUNCTION

The maple sirup evaporator is an open pan
for boiling water from the sap. Although the
primary purpose of the evaporator is to remove
water, it must do the job economically and in
such a way as to improve but never to impair
the quality of the sirup being made.

Maple sirup evaporators have gone through
an evolution in design. The first evaporator,
used by the Indians, was a hollowed log in
which water was evaporated from the sap by
adding hot stones. The next evaporators were
metal kettles used by the white settlers. Both of
these were batch-type evaporators, that is, the
entire evaporation process, from the first addi-
tion of sap to the last, was done in one kettle.
Sap both high and low in sugar content was
added. It might be many hours before the sirup
was finally drawn. As a result, a dark strong-
flavored sirup was produced.

The next improvement in evaporators was
the use of multiple kettles (fig. 77). This evapo-
rator was the forerunner of today's continuous
evaporators.

The sap was partly evaporated in the first
kettle, transferred to the second kettle for fur-
ther concentration, and then finally transferred

to a third and sometimes a fourth kettle where
evaporation was completed. The multiple-kettle
method was a semicontinuous operation and
resulted in an improved (lighter colored) sirup
because the time of heating at near-sirup den-
sity was shortened.

The source of heat for all the early evapora-
tors was an open fire, which is poor in fuel
economy.

The first major change in design of evapora-
tors was the introduction of the flat-bottom pan
and the enclosed firebox (fig. 78). Both the
increased heating surface of the pan and the
confined fire increased the efficiency of the fuel.
This design was quickly followed by partitioned
pans, which were the forerunner of flue-type
evaporators.

The modern flue-type evaporator, developed
about 1900, was the next and last major change
in design. Use of "flues" or deep channels in the
pans, and altering the firebox so that it arched
the hot gases between the flues, caused the hot
gases and luminous flames to pass between the
flues before escaping up the chimney. Fuel
economy was increased. Also, the rate of evapo-
ration was increased, which shortened the

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

Figure 77. — Multiple-kettle method of making maple sir-
up. In this method, the sap was partly evaporated in
the first kettle, then transferred to the second and
third kettles, and finally to the fourth kettle, where
evaporation was completed. (Courtesy of W. W. Si-
monds, Pennsylvania State University.)

l'N-1774

Figure 7H. — The flat pan was the forerunner of the
modern flue pan.

evaporation time, improved the quality of the
sirup, and lowered the cost of production.

Design of Evaporator

The modern flue-type evaporator, which oper-
ates under atmospheric pressure, consists basi-
cally of two sections: (1) The sap pan, in which
the flues are located, and (2) the sirup pan. The
sections are separated to facilitate their re-
moval from the arch for cleaning and repair. A
semirigid pipe or tubing connects the pans. The
connections tend to restrict the free movement
of sap as it travels through the evaporator and
minimize the intermixing of the dilute sap in
one pan with the more concentrated sap in the
adjacent pan.

So that the evaporators can be operated in a
continuous or semicontinuous manner, baffles
or partitions are built in the pans to form
channels through which the sap flows as it is
being concentrated. The location of these parti-
tions and the size and shape of the channels
differ with different manufacturers.

The sap pan can be made with narrow, deep
channels because the sap, while in this pan, is
never concentrated enough to become viscous;
it flows readily. Use of narrow flues increases
the heating surface and thereby increases
transfer of heat. Fresh sap is admitted to the
sap pan through a float valve that can be
adjusted to maintain the desired depth of liquid
in the evaporator (fig. 79).

The sirup pan, often called the fi-ont pan, is
usually located over the firebox. Concentration
of the sap to sirup is completed in this pan. It
has a flat bottom to facilitate cleaning and to
permit evaporation of shallow layers of sirup
without danger of burning.

Changes in Sap During Its Evaixji-ation
to Sirup

Development of the desired maple flavor and
color is the result of chemical reactions that
occur while the sap is boiling in the evaporator.
(See p. 67.) The extent of these reactions is
determined in part by the length of time the
sap is boiled (HI).

Chart 5 shows the effect of length of boiling
period on amount of color {150) produced in sap
of different solids concentrations (" Brix). At low

MAPLE SIRUP PRODUCERS MANUAL

Figure 79. — The float valve on the sap pan adjusts tlie
depth of the Uquid in the evaporator. Different devices
are used to obtain precise valve settings.

ORIG,

BOILING TIME (MINUTES)

C/iari 5.— Effect of length of boiling period on color forma-
tion (color index) in sap of different solids concentra-
tions.

concentrations little color is produced in a given
boiling time, whereas at higher concentrations
more color is produced. The rate of color forma-
tion does not increase appreciably until the
Brix value of the sap reaches 25° or more, and
this occurs after the sap reaches the sirup pan.
To provide a basis for comparing color of
maple saps of different concentrations, color is
expressed as color index. Color index is meas-

ured with monochromatic light in a spectropho-
tometer:

86.3%

Color index = A

1 cm

A.,,„ (86.3/6C)

where A,-,,, is the observed absorbance at 450
millimicrons with distilled water used as the
blank; b is the depth of the solution in centime-
ters; and c is the grams of solids as sucrose per
100 milliliters of solution as determined on an
Abbe refractometer. The maximum color in-
dices for table sirup of various grades are: 0.510
for U.S. Grade AA (Light Amber), 0.897 for U.S.
Grade A (Medium Amber), and 1.45 for U.S.
Gi-ade B (Dark Amber).

Other changes that occur in the sap as it boils
are shown in charts 5 and 6. The rate of color
formation is greatest as the sap approaches the
concentration of finished sirup (150). Thus, the
length of time that sap is heated in the sap pan
(when the Brix value is low) is relatively unim-
portant in the formation of color. In the sirup
pan, however, color develops rapidly as concen-
tration increases.

The rate at which water is removed from sap
at different boiling times and the corresponding
solids concentration are shown in charts 7 and
8.

The curves show that the average time that a
lot of sap with an initial solids content of 2.5°
Brix is in the evaporator is approximately IV^
hours — a little less than 30 minutes in the sap
pan and slightly more than 60 minutes in the
sirup pan. To make high-quality, light-colored
sirup, the time required to evaporate the sap to
sirup must be kept to a minimum. Conditions
that affect the boiling time are: (1) The design
of the evaporator; (2) the amount of heat ap-
plied to the evaporator; (3) the efficiency of the
heat transfer; and (4) the depth of the boiling
liquid. Once an evaporator is selected and pur-
chased, the sirupmaker controls only the
amount and steadiness of heat applied to the
pans and the depth of boiling sap.

Evaporation Time

The evaporation time is measured from the
time a unit of sap enters the sap (flue) pan until
it is removed from the sirup pan as sirup.
Evaporation time should not be measured until
the evaporator is operating steadily, the heat

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

1.5

1.0

1 Color index ^^
\.^-

0.9*

/ \

o
- O

/, 1 , 1 1 1 1 1 1 1 1 L 1 1 1

1,11

1 1.5

1.0

/ ^

Color index ^

^ /
/

/
/

0.5

f-r-;-rr~~r7 1 1 1 1 1 1 1

1 1 1 1

0 20 40 60 80 100

TIME (MINUTES)

Chart 6. — Changes in Brix value, color, and pH in sap
during the evaporation period. A, Soon after evapora-
tion begins the sap becomes alkaline, reaching a pH of
8 to 9; it then decreases in alkalinity until at the end of
the period it is about neutral. Little color is produced
until after the sap reaches a pH of 8, at which point
color increases at a rapid rate. It increases further as
the concentration of the sap approaches that of fin-
ished sirup (30° Brix and above). B, Increase in Brix
value is slow at the beginning and becomes more rapid
as evaporation progresses.

source is constant, the liquid in both the flue
and sirup pans is in a state of full boil, and the
sirup is being drawn off at a constant rate or at
regular intervals. The evaporation (holdup)
time can be lengthened by increasing the level
of liquid in the pans. The lowest depth of liquid
in the evaporator (both pans) will give the
shortest evaporation time. If the depth of liquid
is too low, the pans will bum, so this control is
limited.

Liquid Level in Evaporator

The depth of sap to maintain in the evapora-
tor is determined by a number of factors. Most
important is the minimum depth that must be

maintained to keep the pans from burning.
Many sirupmakers find that a liquid level of 1
inch in the sirup pan is ideal. When the evapo-
rator is operating correctly with a steady
source of heat, there will be a slight gradient or
decline in the liquid level in the evaporator. The
highest level will be at the point of sap intake
and the lowest at the point of sirup drawoff.
With uneven firing, this gradient is upset. Dur-
ing periods of low heat, when the sap is merely
simmering, the gradient is lost. The depth of
the sap tends to become level, and there is an
intermixing of sap of different concentrations.
Intermixing, together with an increase in the
average depth of sap, results in a longer holdup
time and the production of darker sirup. The
lower the Brix value of the sap, the longer the
holdup time, since there must be greater gra-
dient in the sap levels. Since the minimum level
at the point of sirup drawoff is fixed to prevent
burning the pans, the level at the sap intake

1-
z

LlJ

LiJ
Q.

1 1 1 1

Z
<
Q.

Q. 60

—

P4C

2 20

—

\ —

>s.

^^^...^^^

1 1 l" — \

60 90

TIME (MINUTES)

120

150

Chart 7. — The average time (time required to remove 50
percent of the water) that any lot of sap remains in the
sap pan (see dotted lines) is slightly less than 30
minutes. The time can be shortened or lengthened by
using sap of lower or higher solids concentration
(° Brix), by varying the depth of sap in the evaporator,
and by varying the intensity of the heat.

MAPLE SIRUP PRODUCERS MANUAL

60 90 120 150

TIME ( MINUTES)

Chart 8. — The average time (time required to remove 50
percent of the water) that any lot of sap remains in the
sirup or front pan (see dotted Hnes) is a little more than
60 minutes. The time in this pan can also be shortened
or lengthened by changing the Brix value of the sap
entering the sirup pan, by varying the depth of the sap,
and by varying the intensity of the heat.

must be adjusted to keep the sap proportion-
ately deeper. A change in the Brix value of the
sap in the supply tank requires a readjustment
of the float of the intake valve. Changing to sap
with a higher Brix value without readjustment
may result in a burned pan.

Rates of Evaporation

The solids concentration of the sap is about
doubled before it leaves the sap pan, that is,
nearly 50 percent of the water that is to be
removed has been evaporated {111, 140). By the
time the sap reaches a concentration of only 19°
Brix, 90 percent of this water has been evapo-
rated.

The changes in the concentration of a typical
sap (2.5° Brix) during evaporation are given in
table 4.

A two-section evaporator with three channels
in the sap (flue) pan and four in the sirup (front)

pan and the points at which the concentration
was measured (table 4) are shown in chart 9.
To make 1 gallon of standard-density sirup

from this sap required , or 34.4 gallons of

2.5
sap; 33.4 gallons of water had to be evaporated.
The solids concentration of the sap was doubled
(from 2.5° to 5.0° Brix) in the sap pan. This re-
moved 17.3 gallons of water, or more than 52

Table 4. — Changes in the solids concentration
of sap (° Brix) and water evaporated in a
simulated evaporator, for each gallon of sirup
produced

Solids
concen-
tration

Water ev

aporatec

Section of
evaporator

Per section

Total

of sap

Gal-

Per-

Gal-

Per-

"Brix

lons

cent

lons

cent

Original sap

2.5

Sap pan:

First section ___

. 3.0

5.77

17.35

5.77

17.35

Second section _

_ 3.7

5.40

16.24

11.17

33.59

Third section

. 5.0

6.16

18.53

17.33

52.12

Sirup pan:

Fourth section ,

_ 8.0

6.45

19.40

23.78

71.52

Fifth section ___

_ 19.0

6.26

18.83

30.04

90.35

Sixth section

_ 42.0

2.48

7.46

32.52

97.81

Seventh section

54.0

.45

1.35

32.97

99.16

Finished sirup - _

- 65.5

.28

.84

33.25

100.00

' Percentage of sugar.

- When this experiment was conducted, the Brix of
standard sirup was 65.5°.

^S\

Chart 9. — Top view of a simulated maple sap evaporator
having 3 channels in the sap pan and 4 channels in the
sirup pan. Arrow shows direction of sap flow. The solid
circles show the location of sap of different solids
concentrations (° Brix), as indicated in table 4.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

percent of the 33.4 p:allons of water that had to
be removed to make 1 gallon of sirup. By the
time the solids had increased to only 19° Brix, 90
percent of the water had been removed, and the
sap had progressed only halfway through the
sirup pan. Thus, the remaining 10 percent of the
water was removed in the last half of the sirup
pan. This shows that most of thf water is evapo-
rated while the solids are at sufficiently low con-
centrations to have little effect on the color of
the sirup. It also shows that sap must be kept
moving forward through the pan as it ap-
proaches sirup concentration, so that it can be
removed from the evaporator as quickly as pos-
sible.

This also explains why adding one or more
sap (flue) pans in a series does not increase
evaporation time but does increase evaporation
rate and capacity. Lengthening the evaporator
system by increasing the number of feet that
the sap must travel through the different chan-
nels makes use of the engineering rule that
evaporation (heat transfer) increases as the
rate at which the liquid moves over a heated
surface increases. Thus, lengthening the evapo-
rator by using supplementary flue pans will not
increase holdup time; it actually decreases it.

Therefore, the percentage of solids (weight-vol-
ume) of the sirup divided by the Brix value of
the sap equals the number of gallons of sap
required to produce 1 gallon of sirup. The equa-
tion is:

where a = the numberofgallonsofsap to produce
1 gallon of standard-density sirup.

X = the Brix value of the sap (to represent
the solids concentration of the sap).

Fi"om this number, 1 is subtracted to obtain
the number of gallons of water that must be
evaporated from the sap to obtain 1 gallon of
sirup. The following equation is used:

Example: With sap having a density of 2.4°
Brix,

S6_
2.4

1, or 36 - 1 = 35,

the number of gallons of water that must be
evaporated to obtain 1 gallon of standard-den-
sity sirup.

Ride of 86

The amount of water that must be removed
to reduce the sap to sirup varies with the solids
concentration of the sap.

The "Rule of 86" can be applied to determine
the number of gallons of a particular sap re-
quired to produce 1 gallon of standard-density
sirup. The number 86 is used in the calculation
as representative of the percentage of solids (as
sugar) on a weight-volume basis that is found
in a gallon of standard-density sirup. (Until
1974 the standard density for maple sirup was
65.5° Brix, and sirup of this density contains
86.3 percent solids as sugar. Now that the
standard density is 66.0° Brix, the percentage of
sugar in a gallon of standard sirup is actually
87.2, but the traditional "Rule of 86" persists in
the industry and is quite satisfactory for practi-
cal purposes.)

Since the solids concentration of sap is com-
paratively low, its Brix value and percentage of
solids (weight-volume) are essentially the same.

Suniniaiy

(1) The modern evaporator is an open-pan, flue
type and has a high evaporation efficiency.

(2) The major changes that affect sirup quality,
color, and flavor occur after the sap has
been concentrated to 45° Brix.

(3) The development of color and flavor depend
on the length of time sap with a Brix value
of 45° or higher is boiled.

(4) Evaporation rate is increased if the path
the sap travels over the heated surfaces is
lengthened.

(5) Use of multiple sap pans assembled in series
increases the rate of evaporation.

(6) The time required for the last stage of
evaporation is determined by the holdup
time (depth of sap in evaporator, last section
or in finishing pan) and the intensity of the
heat.

(7) Pi'oduction of light-colored sirup is favored
by shallow depth of sap in the evaporator
and by intense constant heat.

MAPLE SIRUP PRODUCERS MANUAL

OPERATING THE EVAPORATOR

Starting the Evaporatoi-

The sap is run into the evaporator until the
bottom of the front pan is covered to a depth of
1 inch; then the fire is lit. As soon as the sap
begins to boil, the sap inlet float valve is ad-
justed to maintain the desired depth of liquid
(V2 to 1 inch) in the sirup pan. As water evapo-
rates, the float valve admits more sap (fig. 79).

If sirup has not been made previously, a
series of adjustments of the float will be neces-
sary to be sure the liquid in the sirup pan i
always maintained at a depth of '/., to 1 inch at
the point of drawoff.

The constant addition of sap keeps the sap in
the pan dilute. It becomes progressively more
concentrated at points farther from the sap
inlet. The sirup di-awoff is at the farthest point.

Saps of different solids concentrations (° Brix)
require different adjustments of the inlet-valve
regulator to maintain the same depth of sirup
in the front pan. The depth of sap in the sap
pan must be gi-eater for sap with a Brix value
of 1° than for sap with a Brix value of 2° and it
must be lower for sap with a Brix value of 3°.
By checking the Brix value of the sap in the
storage tank, the float valve can be set to
maintain the desired depth of sap in the evapo-
rator. The Brix value should be checked with a
hydrometer every half hour or whenever a new
lot of sap is run into the storage tank. This will
prevent burning the pan, which might happen
with a change to sap with a lower BrLx value
unless the depth of liquid is increased.

The pipeline between the storage tank and
the evaporator must be large enough to assure
a constant and adequate supply of sap to the
evaporator, so that a constant level of sap is
maintained. If this pipe is connected to an
outside storage tank, it must be insulated to
prevent the sap from freezing in the line. Were
this to occur, the supply of sap would be cut off
and the pans would burn.

The sap feed line should be equipped with a
fast-acting valve that can be used to adjust the
flow of sap and to stop the flow when the
evaporator is taken out of use. A secondary sap
feed line should also be installed. This line
should be equipped with a flexible hose long

enough to reach any part of the evaporator or
finishing pan. This is an emergency line for use
whenever there is a stoppage in the main feed
line or for quickly supplying sap to any part of
the evaporator where sap is needed to prevent
burning the evaporator.

Drawing Off the Siiiip

The boiling point of standard-density sirup is
7° F. above the boiling point of water. This is
discussed in detail in the section "Elevation of
Boiling Point," page 72.

Any thermometer that has a range of 200° to
230° F. and a sufficiently open scale can be used
to determine the boiling point of sirup. It
should be calibrated in V2° and preferably in V4°.

With older procedures, it was customary to
make finished sirup in the evaporator. It was
seldom possible to continuously remove sirup of
standard density from the sirup pan, except in
very large evaporators. Instead, the sirup was
removed discontinuously or in batches. The last
channel of the sirup pan was in effect a finish-
ing pan. This caused the following undesirable
conditions: The sirup channel was seldom iso-
lated, so that the turbulence of the boiling sirup
caused a constant intermixing of the finished or
nearly finished sirup with less concentrated
sap. This lengthened the holdup time (time sap
is heated) and occurred when heating is a
critical factor in flavor and color development.
Also, each time a lot of finished sirup was
drawn off, some sirup had to be left in the last
channel of the evaporator to keep the evapora-
tor from burning. The sirup that was left was
then mixed with the next lot of dilute sirup.
The prolonged heating period darkened the
color.

However, when this procedure is followed,
the drawoff valve must be opened as soon as
the boiling sirup reaches a temperature 7° F.
above that of boiling water. The temperature of
the boiling sirup should be watched closely to
be sure it neither rises above nor falls below
this temperature, and the sirup should be
drawn off at a rate to maintain this tempera-
ture. If the boiling sirup falls below the proper
temperature, the drawoff valve should be closed
immediately.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE
Finishing Pan

Because of the difficulties of finishing the
sirup in the evaporator, use of a separate fin-
ishing pan is recommended (figs. 80 and 81). A
separate finishing pan permits (1) complete re-
moval of the almost finished sirup (45° to 60°
Brix) from the evaporator, so that there is no
possibility of intermixing with less concen-
trated sirup; (2) complete control of finishing
the sirup without extending the total time the
sap is heated; and (3) complete removal of the
finished sirup from the pan.

The size of the finishing pan is determined by
the size of the evaporator. Partly finished sirup
should be removed ft-om the evaporator at least
once each hour and finished in batches. Since
sirup transferred to the finishing pan will have
a solids concentration of not less than 45° Brix
and since it requires 2 gallons of 45°-Brix sirup
to yield 1 gallon of 66.0°-Brix (standard-density)
sirup, an evaporator that has a rated capacity
of 4 gallons of finished sirup per hour requires a
finishing pan that holds 8 gallons of 45°-Brix
sap and provides additional space to take care
of foaming. A pan 18 inches square will hold
approximately 1.5 gallons for each inch of
depth. Therefore, to accommodate 8 gallons of
45°-Brix sap the pan should be 5 inches deep
and should have an additional 10 inches for
foaming. The pan will therefore be 18 inches
square and 15 inches deep. It should have
handles and a cover and should be equipped
with a precision thermometer having a range of
200° to 230° F. in V2° or preferably V4° divisions
and a sirup drawoff cock. Preferably, the pan
should be heated by gas flame since gas heat
can be easily adjusted and can be shut off when
the sirup reaches the desired boiling tempera-
ture.

For convenience two finishing pans can be
used alternately. When a finishing pan is used,
the sap being drawn from the evaporator for
transfer to the finishing pan need not be of
constant density. It can be any density above
45° Brix (3° or more above the boiling point of
water). The higher the density of the sirup that
is withdrawn from the evaporator, the smaller
the amount of liquid that has to be evaporated
in the finishing pan.

Another and important advantage of using a
finishing pan is that it permits filtering the

mmM.

1 ' 1 ^

PN-4776

Figure 80. — The finishing pan allows complete control
over the final stage of the evaporation of sap to sirup.
Generally, the fuel is bottled gas.

sirup that is being transferred from the evapo-
rator to the finishing pan. Sirup at this density
(45° to 60° Brix) has essentially all of its sugar
sand (see p. 78) precipitated. At this density, it
has a viscosity (fluidity) only slightly higher
than water and filters much more readily than
does standard-density sirup.

In some installations, the sirup is pumped
from the finishing pan to the holding or can-
ning tank. A cartridge-type filter can be placed
in this pipeline to serve as a polishing filter. It
will remove any sugar sand that was not re-
moved by the major filter or that may have
been formed in the finishing pan.

Many producers using bottled gas to heat the
finishing pan report that the cost of fuel is
approximately 7 cents per gallon of finished
sirup.

A finishing pan is always used in conjunction
with a complete evaporator (flue pan plus flat
pan). The flat or sirup pan of the evaporator
serves as a semifinishing pan. The capacity of
the evaporator is readily expanded by adding
one or more flue (sap) pans, each with its own
arch and separate heat source (preferably oil).

MAPLE SIRUP PRODUCERS MANUAL

PN-4771

Figure 81.— A steam-heated finishing pan, Uke a gas-fired pan, provides positive control of the finished sirup and

eliminates danger of scorching.

When a finishing pan is used, the following
procedures should be observed:

(1) Do not finish more than 5 to 10 gallons of
sirup in a batch.

(2) When the sirup is finished, that is, when it
reaches the proper temperature (7° F. above
the exact boiling point of water), heating must
be stopped immediately.

(3) Drain all the finished sirup from the pan.
If any sirup is left in the pan, it will darken the
next batch.

(4) Use two finishing pans alternately.

Aiitoinatic Drawoff

An automatic drawoff is well suited for draw-
ing the partly evaporated sap from the evapo-

rator for later completion in the finishing pan
(fig. 82). A high precision thermoregulator is not
required, since a tolerance of ±0.5° F. is accept-
able. Corrections need not be made for slight
changes in the boiling point caused by changes
in barometric pressures throughout the day.

Automatic valves can be purchased as com-
plete packages, or they can be assembled as
indicated in chart 10. These valves are operated
by a solenoid, which in turn is opei-ated by a
thermoregulator. The thermoregulator is ad-
justed by hand to open or close the valve when
the boiling sirup reaches the desired tempera-
ture, as measured by a precision thermometer.

A thermoregulator, if used to control the
removal of finished sirup from the evaporator

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

AUTOMATIC SIRUP DRAW OFF
MECHANICAL ASSEMBLY

EVAPORATOR PAN

THERMO-i
SWITCH

0 5 MICROFARAD 600 VOLT

OIL-FILLED CONDENSER

OR TYPE 8A5PS5 (ITT) FEDERAL

CONTACT PROTECTOR

FOR 117 V AC OR EQUAL

Chart 10. — Automatic sirup drawoff.

or finishing pan, must be sensitive to changes
of ±0.1° F. The thermoregulator must be recaH-
brated three times a day.

When the thermoregulator is operated on 110
V. a.c, a condenser must be shunted across the
line (see chart 10) to protect the contact points
against the surge of heavy current that is set
up each time the solenoid coil operates. To
avoid this, it is better to operate the thermo-
switch on low d.c. voltage and use a high-
capacity mercury relay to operate the solenoid
valve.

Another type of temperature regulator uses
thermistor probes as the sensing element. A
sensitive electrical relay must be used w^ith this
type of regulator, and it is recommended for use
with the thermoregulator.

The thermistor probes in the boiling sirup
must be kept free of sugar-sand deposits. De-
posits of sugar sand on the probes will change
their heat-transmitting properties and cause
error in their response to the sirup boiling
temperatures. The probes can be kept free of
sugar sand by soaking them in 10-percent sul-
famic acid between runs. This same precaution
applies to the bulb of the thermometer.

A further advance in controlling automatic
drawoff has been made at the Eastern Regional
Research Center (15). A new thermoregulator

PN-n78

Figure 82. — The automatic drawoff is especially well
suited for removing sirup from the evaporator. When a
finishing pan is used, the evaporator functions as a
semifinishing pan.

containing a Wheatstone bridge, thermistor
probes, and a meter relay automatically com-
pensates for changes in boiling point caused by
changes in barometric pressure (fig. 83). The
instrument employs two thermistor probes. The
water probe continually responds to changes in
the temperature of boiling water. The sirup
probe causes the valve to open whenever the
temperature of the boiling sirup reaches a pre-
determined number of degrees above the tem-
perature of the boiling water — T F. for stand-
ard-density sirup and slightly more for heavier
sirup.

End uf an Eva|K>i'ation

When the evaporation of a run of sap has
been completed, care must be taken or the pans
may be burned. If water is available, it can be
run into the storage tank as the last of the sap
is being withdrawn. Little sap will be lost, and
the pans can be flooded with .3 to 5 inches of
water before the fire is extinguished. This pre-
caution is necessai-y when either wood or oil is
used because enough heat will remain in the

MAPLE SIRUP PRODUCERS MANUAL

Figure 8S.— Automatic thermoregulator that compen-
sates for changes in barometric pressure.

firebox and arch to melt the solder and the thin
metal of the pans if the pans become dry before
the firebox has cooled.

If water is not available, the fires must be
extinguished and evaporation stopped while
there is still enough sap in the storage tank to
fill the evaporator to a depth of 3 to 5 inches.

Cleaning the Evaporator

When maple sap is concentrated to sirup in a
flue-type open-pan evaporator, the organic salts
become supersaturated; that is, they are con-
centrated to a point where they can no longer
be held in solution. They are then deposited on
the sides and bottom of the evaporator as a
precipitate or scale. This scale forms an imper-
vious layer that builds up with continued use of
the evaporator. The scale reduces heat-transfer
efficiency and thus wastes fuel and holds up
sirup in the evaporator unduly.

The scale is of two types. One type is a
protein-like material that forms in the flue or
sap pans. The other, called sugar-sand scale,
forms in the sirup or finishing pan. It is a
calcium and magnesium salt deposit similar to
milkstone and boiler scale.

Sugar-sand scale is the more troublesome of
the two types. It is esi^ecially troublesome if it
is allowed to build up to an appreciable thick-

ness. Also, sugar sand contains entrapped cara-
melized sugar, which contributes to the produc-
tion of dark-colored sirup.

Removing sugar-sand scale is not easy, and
doing it by physical means (scraping, scrubbing
with steel brushes, or chiseling) is almost im-
possible. Removal becomes more difficult as the
layer of scale becomes thicker. Clean the evapo-
rators often enough to prevent buildup of sugar
sand. Teflon-coated pans are easier to clean.
Also, keep the underside of the flues clean.

Mptlioils I'scd ill file Past

Some methods used in the past to prevent
formation of scale and to remove thin layers
include —

(1) Reversing the flow of sap through the
evaporator, according to the manufacturer's
directions; this retards the formation of scale.

(2) Running soft spring water through the
evaporator for a long period; this tends to
dissolve small amounts of scale.

(3) Pouring skim milk into the pan and letting
it remain until it sours; the lactic acid of the
sour milk has some solvent action on the scale.

(.Iieiiiirtil (.le<iners

Equipment manufacturers have used mu-
riatic acid to remove heavy incrustations of
sugar-sand scale from evaporators returned to
them by maple-sirup producers. This acid is
highly corrosive and must be used with gi-eat
care to avoid damaging the pans by dissolving
the thin tinplate coating. Also, unless a person
is experienced in the use of muriatic acid, there
is danger that he will get the acid on other
materials or on his skin.

Laboratory and field tests have shown that
sulfamic acid (121), one of the chemicals devel-
oped for cleaning milk-processing equipment
and marine boilers, can be used to remove
sugar sand from most maple sirup equipment.
Sulfamic acid (the half amide of sulfuric acid) is
an odorless, white, crystalline solid and is
highly soluble in water. It must not be confused
with sulfuric acid. Sulfamic acid crystals can be
handled easily, with little risk of spilling and
little danger from volatile fumes. As a solid,
sulfamic acid is reasonably harmless to the skin
and clothing. However, a solution of the acid
can irritate the skin. If either the dry acid or its
solution comes into contact with the skin, it

AGRICULTURE HANDBOOK 134, U.S. DEFT. OF AGRICULTURE

should be washed off immediately with large
quantities of water. Also, it should be removed
from clothing and equipment by rinsing repeat-
edly with large quantities of water. Bulk sup-
plies should be stored in a tight container in a
dry place.

Despite its strong acid characteristics, sul-
famic acid has only a slight corrosive action on
most metals except zinc plating, especially if
contact is for a short period. For example, on
tin (the metal coating of most evaporators),
hydrochloric acid is almost 25 times more corro-
sive than sulfamic acid and sulfuric acid is
approximately 80 times more corrosive.

Gluconic acid, another chemical cleaner, is
recommended for cleaning galvanized-iron
equipment because it has much less corrosive
action on the zinc coating. However, use of
gluconic acid need not be limited to cleaning
galvanized equipment; it is effective on most
metals, even though it has a slower cleaning
action than sulfamic acid. It is usually sold as a
50-percent water solution.

Both sulfamic acid and gluconic acid can be
obtained from suppliers of maple sirup equip-
ment.

Use these amounts of acid:

Sulfamic Acid. — For a thin scale, use V4
pound (V2 cup) per gallon of water. (This is a 3-
percent solution.) For a heavy deposit, use V2
pound (1 cup) per gallon of water. (This is a 6-
percent solution.)

Gluconic Acid. — For all deposits, use 1 gallon
of 50-percent stock solution (obtained from your
supplier) for each 4 gallons of water. (This is a
10-percent solution.)

To avoid damaging the tinned surface of the
evaporator, do not use a stronger solution than
recommended; and do not leave the solution in
the evaporator longer than is required to soften
the scale.

Cleaning Procedure

Use the same methods to clean the flue (sap)
pans and the sirup (finishing) pan.

You will need a good supply of piped water, so
that you can use a hose to rinse the pans. If
water is not available at the evaporator house,
take the evaporator pans to a source of piped
water.

You should wear rubberized gloves to protect
your hands from the acid solution.

The best maintenance practice is to remove
the sugar-sand scale between each run. The
following procedure should keep the evaporator
clean and bright: With a cloth, swab the pans
with the acid-cleaning solution; allow it to re-
main a few minutes; then thoroughly rinse the
pans with water, to be sure the acid is com-
pletely removed.

If a layer of scale has accumulated on the
evaporator, use the following procedure:

(1) Remove all loose scale and dirt from the
pan with a broom or brush. Then rinse the pan
with a good stream of water from a hose.

(2) Plug the outlets of the pan. If the outlets
have threaded fittings, use metal screw plugs;
othei-wise, use wood, cork, or rubber stoppers.

(3) Fill the pan with water to the level to be
descaled. Measure the water as you put it in
the pan, and make a record of the number of
gallons for future use. Also, make a I'ecord of
the estimated volume of the pan.

(4) Add the correct amount of acid to the
water in the pan. Stir to help dissolve the acid.

(5) Warm the solution in the pan to a temper-
ature of 140° to 160° F. This hastens the rate at
which it softens or dissolves the scale. After the
warm solution has been in the pan for a short
time (usually 15 to 20 minutes is enough), brush
the sides and bottom of the evaporator with a
fiber brush to speed up removal of the depos-
ited sand.

(6) When the evaporator is clean, drain the
acid from the pan. Turn the pan on its side and
flush it out with a stream of water. Repeat the
water rinse five or six times, and allow the pan
to drain between each flushing. Thorough rins-
ing is necessary to insure complete removal of
the acid and its salts from the pan.

To remove a thin layer of scale with sulfamic
acid requires from 30 to 35 minutes; to remove
a thick layer requires from 60 to 90 minutes.
With gluconic acid, about twice as much time is
required. The acid solution can be stored and
reused a number of times. Do not store it in
iron or galvanized containers; glass or earthen-
ware containers are best.

To economize on the amount of acid, use a
smaller quantity of solution and tilt the pan

MAPLE SIRUP PRODUCERS MANUAL

first in one position and then in another until
all the scale-covered surfaces have been soaked.
Sulfamic acid and its salts are toxic to grow-
ing plants. For this reason, it is an effective
weedkiller. But care should be taken not to
discard the used acid solution where desirable
plants may be damaged or killed.

Endrof-Senson Cleaning

A much-used procedure for cleaning evapora-
tor pans at the end of the season is to fill them
with sap and let them stand several weeks. The
sap will ferment and the acids formed will
loosen the scale. If the sap becomes ropy and
jellylike, it will be difficult to remove. However,
if it is allowed to stand longer, it will again
become liquid and can be removed easily. As
with the other cleaners, the pans must be
rinsed after the fermented sap treatment and
dried before they are stored. Fermented sap
will not remove heavy scale deposits.

Whether to clean the evaporator at the end of
the sap season is debatable. Some producers
store the evaporator pans with the deposit,
assuming that this serves as a protective coat-
ing and keeps the evaporator surfaces from
corroding. The preferable method is to clean the
equipment so that it is ready for use the next
spring. In either case, the evaporator pans
should be dried and stored in an inverted posi-
tion.

Smninaiy

(1) Use a flue-type open-pan evaporator as the
basic unit.

(2) Evaporate more than 90 percent of the
water in the evaporator. The sap should
have a Brix value of 45° to 60°.

(3) Complete the evaporation in a finishing
pan.

(4) To expand the evaporation, add one or
more flue pans and operate them in series.

(5) Operate the evaporator with a minimum
depth of sap. Keep the depth of sirup at
point of drawoff at V2 to 1 inch.

(6) Keep sap boiling vigorously at all times.

(7) For wood fires keep the fire uniform and
keep the fire doors closed except when
adding fuel.

(8) If a finishing pan is not used, draw off the
sirup as soon as it reaches the proper
boiling temperature (7° F. above the boil-
ing point of water for that hour and place).

(9) If a finishing pan is used, draw off the
sirup at 45° to 60° Brix (boiling tempera-
ture at drawoff 2.5° to 5.1° F. above the
temperature of boiling water). Use an au-
tomatic valve controlled by a thermo-
switch.

(10) Filter the sirup in transferring it from the
evaporator to the finishing pan.

(11) As soon as the temperature of the boiling
sirup in the finishing pan rises 7° F. above
the boiling point of water (which yields
standard-density sirup; 7.5° above the boil-
ing point yields 67°-Brix sirup with better
taste), immediately stop heating, cover the
pan and withdraw the sirup.

(12) Clean the evaporators often enough to pre-
vent buildup of sugar sand.

(13) Rinse the evaporator pans with large
amounts of water (use three separate rin-
ses, draining the pan between each rinse
after each time a chemical cleaner is used
in the evajwrator or finishing pan).

(14) Keep the underside of the flues clean.

OTHER T^ PES OF EVAPORATORS

Other types of evaporators include the steam
evaporator (or a combination of oil and steam)
and the vacuum evaporator.

Stoain Evaporator

The evaporation of maple sap with high-
pressure steam (figs. 84-86 and chart 11) is
practiced by a few producers {97). Its use, how-
ever, has never become widespread. Steam

evaporators have several advantages, as fol-
lows: (1) The heat is steady; therefore, the sap
can be evaporated at a continuous and even
rate. (2) Heat can be supplied in steam coils,
manifolds, or a jacketed kettle. (3) The evapora-
tor can be constructed with smooth walls; flues
are unnecessary. (4) Scorching of sirup is mini-
mized. (5) The evaporator room can be sepa-
rated from the boiler room, which makes it

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

PN-4780

Figure 8J,. — High-pressure steam boilers are economical
when low-priced fuel is available. Approximately 20
gallons of finished sirup per hour can be made in the
two 100-h.p. boilers shown.

Figure 86. — This evaporator consists of several units
connected in series with the partly evaporated sap
moving successively to the next evaporator by means
of a float control to prevent intermixing of concen-
trated sap with less concentrated sap.

easier to keep clean. (6) The high-pressure
steam can be used as the source of heat in
making a variety of maple products. (7) Where
soft coal can be obtained cheaply, high-pressure
steam is economical.

The disadvantages of steam evaporators are:
(1) A license may be required to operate a
steam boiler. (2) The boiler needs periodic in-
spection and overhauling. (.3) In some areas the
water is not suitable for use in a steam boiler.
(4) The initial cost of the steam boiler may not
be justified.

The approximate size of a steam boiler (boiler
horsepower, b.h.p.) required to evaporate sap to
sirup can be calculated, since 1 b.h.p. will evapo-
rate approximately 3.25 gallons of water (sap)
per hour. The value 3.25 varies slightly, depend-
ing on the temperature of the sap as it enters
the evaporator and the operating pressure of
the boiler. As indicated earlier, 33.25 gallons of
water must be evaporated from sap with an
initial Brix value of 2.5° to produce 1 gallon of

/ 33.25 *
sirup. Approximately 10 b.h.p.

3.25

will be

PN-nsi
Figure 85. — A converted evaporator that uses high-pres-
sure steam coils with steam generated by two 100-h.p.
boilers.

required to produce 1 gallon of sirup per hour.

A system that is proving successful is the
combination of oil and steam. In this two-stage
system, oil is used to concentrate the sap to
about 30° or 40° Brix in flue pans, and steam is

MAPLE SIRUP PRODUCERS MANUAL

HIGH PRESSURE
STEAM SUPPLY

^ LARGE VAPOR VENTS ^

REMOVABLE
^COVERS

3 PARTITIONS
IN FINISHING PAN

STEAM TRAP

CONDENSATE RETURN

FLOAT VALVE IN BOX
ON EACH UNIT

DRAW -OFF VALVE

■FILTER BOX

FINISHED SIRUP

Cha)i 11. — Multiple-unit steam evaporator.

used to complete the evaporation. This combi-
nation has all the advantages of steam for
finishing the sirup, but requires a smaller, and
therefore less expensive, steam boiler.

Va<'iiiiiii E\u|>«>rator

Milk-concentration or fruit-juice evaporation
plants in maple-producing areas can be adapted
for evaporating maple sap. This was done dur-
ing the 1930's at Antigo, Wis., where a milk
plant was used to make sirup during part of the
day in the spring sirup season (3).

The procedure used at Antigo is as follows:
The sap is concentrated to between 25° and 30°
Brix in the conventional open-pan evaporator
at the farm site. This is 90 percent of the
required evaporation. Evaporation is completed
in a vacuum evaporator at the central sirup-
finishing plant. This two-stage method of evap-
oration results in a nearly colorless and flavor-
less maple sirup. Such sirup is not marketed for
direct use, but it is ideal for the production of
high-flavored sirup, as described on page 106.

A study at Cornell (42) showed that the use of
milk-plant equipment during off-jieak seasons
for evaporating maple sap was practicable but
that the sirup pi-oduced had to be treated by
the high-flavoring process to obtain marketable
maple sirup. The fixed costs for use of milk-
plant equipment are negligible. However, the
perishable, partly concentrated sap must be
transported to the milk-concentrating plant,
and use of a central sirup-finishing plant re-
quires a new procedure for maple-sirup produc-
tion.

Siimiiiaiy

(1) The steam evaporator provides a steady
source of heat, and danger of scorching is
minimized. The sirup produced is light col-
ored and delicately flavored. However, the
steam evajwrator is expensive to install. A
combination oil-and-steam system (two-
stage method of evaporation) is proving suc-
cessful; it has all the advantages of steam
but is less expensive to install.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

(2) The vacuum evaporator, which is Hmited to
large-scale or central-plant operation, is
used to complete the evaporation of sap that
has been partly concentrated on the farm.

The equipment used usually is idle milk-
evaporation equipment. The sirup produced
has essentially no maple flavor, but it is
excellent for use in making high-flavored
sirup.

FUEL

Wood

The modern flue-type evaporator was de-
signed for burning wood. A wood fire carries a
luminous flame throughout the entire length of
the arch. The flue area of the evaporator and
the part that lies over the firebox are heated
both by radiant and by convection heat liber-
ated by the burning gases. The wood may be
sound cordwood, defective trees removed in
improvement cuttings, or sawmill wastes —
either culls or slab (69).

In the evaporation process, the object is to
evaporate the water in the shortest possible
time. Therefore, it is essential to use only diy,
sound wood that will produce a hot fire. Wet or
green wood will not produce as much heat as
will the same volume of dry wood. Poor burning
fuel results in a slower boiling rate. This, in
turn, causes the sap to be held in the evapora-
tor for a longer time and results in a darker
sirup.

A steady fire shortens the boiling time. The
best results are obtained by charging the fire-
box first on one side and then on the other,
keeping the fuel in the firebox at almost con-
stant volume (fig. 87). The fire doors should be
closed immediately after each charging to re-
duce the intake of cold air which cools the
underside of the pans. When this happens, the
boiling rate of the sap decreases and holdup
time in the evaporator increases. Likewise, ash-
pit draft doors that are open too wide will admit
more air than is required for combustion, and
the excess air has a cooling effect. Introduction
of cold air beneath the evaporator pan in either
the firebox or the flue area not only reduces the
boiling rate but also tends to set up counter
currents in the flowing sirup in the different
channels of the evaporator. This also contrib-
utes to the production of a darker sirup.

Based on $25 per cord of wood, the fuel to
produce a gallon of sirup would cost about $L

This represents about 10 percent of the cost of
sirup production (5, 113). The heating values of
different wood fuels expressed in British ther-
mal units (B.t.u.'s) for a standard 4- by 4- by 8-
foot cord are maple, 22,800,000; beech,
20,900,000; and hickory, 24,800,000.

The advantages offered by using oil as the
heat source for evaporating maple sap to sirup
are numerous (lOi). Chief among these are (1) it
is automatic; therefore, it does not require the
services of a fireman; (2) it provides a steady
uniform heat, which is desirable for producing
high-quality sirup; (3) it is clean and therefore
aids in better housekeeping and sanitation in
the evaporator house; and (4) in terms of Brit-
ish thermal units, the cost of oil at 35 cents per

PN^783

Figure S7.— When both doors are opened for firing, the
excess air admitted chills the pan. Boiling stops; sap
and partly evaporated sirup intermix; and then, when
the fuel is again burning briskly, the evaporator must
equilibrate itself.

MAPLE SIRUP PRODUCERS MANUAL

gallon is more than double the cost of wood at
$25 per cord, but the operational costs may not
differ greatly since oil does not require the
services of a fireman.

The disadvantages of using oil as the fuel
source, while few, are nevertheless important:
(1) The initial cost (capital investment) of oil
burners is high; (2) oil burners require a special
arch (firebox) although in a new installation it
is not necessarily more expensive than the
conventional wood-burning arch; and (3) oil
does not make use of the cull trees that must be
removed each year from a well-managed sugar
bush.

When oil is used as fuel, two pertinent facts
must be observed. The first and most important
is that wood and oil burn in different ways.
Wood burns with a luminous flame (long fire
path) throughout the length of the evaporator,
including the area under the flue pans as well
as under the sirup pan; oil, on the other hand,
burns as a ball of flame in only a relatively
small space. Secondly, of the two forms of heat
transfers — radiant and convection — used in a
sap evaporator, radiant heat accounts for ap-
proximately 80 percent of the heat transfeiTed
to the liquid, whereas convection heat (that
which is derived from the hot flue gases passing
over the surface of the pans and flues) supplies
approximately 20 percent. Therefore, to make
use of the radiant heat from the oil fire, the ball
of burning oil must illuminate the entire under-
surface of the pans. This necessitates properly
positioning the ball of burning oil and eliminat-
ing any obstructions that will prevent illumina-
tion of the entire undersurface of the pans. This
requirement will be met only through the
proper design of arches made for the burning of
oil as fuel.

A wood-burning arch cannot be successfully
converted to an oil-burning arch without major
changes. The principal fault of such a conver-
sion is that the slope of the wood-burning arch
behind the firebox does not permit illumination
of the entire underside of the sap or flue pan by
the ball of burning oil and, consequently, the
sap will not boil.

Size of Burner

The size of burner to use is determined by
two factors: (1) The length and width of the

evaporator (the vertical area of the flues has a
minor effect) and (2) the quantity of sap to be
evaporated per hour. If the rated capacity of
the evaporator in gallons of sap per hour is
known, it can be divided by 13 (the approximate
number of gallons of water evaporated per hour
by 1 gallon of oil) to obtain the size of burner
(g.p.h. = gallons of oil per hour) required for a
specific evaporator.

The rated capacity of an evaporator burning
wood cannot be accurately equated to that of
an evaporator burning oil. Therefore, this
method of calculation may indicate a burner
that is too large. However, this is not serious
since the amount of oil burned per hour can be
changed, within limits, by changing the size of
the nozzles.

To prevent damaging the pan by firing with
an oversize burner, it is recommended that for
the first trials a nozzle size 20 percent smaller
than indicated by the above calculation be used.
The burning rate (nozzle size) can then be
increased as needed. An empirical method for
determining nozzle size is to divide the surface
area (length times width) by .5. Thus, a 5- by 12-
foot evaporator would require an oil burner
nozzle of 12 g.p.h.

Tyite of Burner

With few exceptions, high-pressure oil burn-
ers that use No. 2 oil are recommended. They
are available with different nozzle sizes to fit
evaporators of all sizes. Their lower initial cost
offsets any advantage gained by using burners
that require the heavier grades of oil.

Muniber of Burners per Arch

Only one burner is required for each evapora-
tor (fig. 88). It must be correctly positioned
under the evaporator and the combustion
chamber must meet certain minimum stand-
ards. Use of a single burner reduces the capital
investment and installation costs. For example,
the capital investment and installation costs for
an evaporator requiring 12 gallons of fuel per
hour supplied by a single burner would be
approximately half that for an evaporator sup-
plied by two 6-gallon-pei--hour burners. In addi-
tion, the two smaller burners will require more
servicing and attention than will the larger
one.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

PN-4'H.l

Figure S8. — A correctly positioned, single, high-pressure,
domestic-type burner will give the required heat for the
evaporation of the sap.

If one burner is used, it should be mounted
far enough below the bottom of the pan so that
the radiant heat will be effective across the full
width of the pan. If construction of the arch
does not permit mounting the burner this far
below the pan (see table 5), then two or more
smaller burners mounted horizontally should
be used to insure heating the full width of the
pan (fig. 89). If the slope of the arch is such that
the undersurface of the flue pan cannot be
illuminated by the ball of fire (see chart 12),
boiling may not occur in the area not illumi-
nated. This is especially true of wood fuel
arches that have been converted for oil burn-
ers. To compensate for this, a supplementaiy
firebox can be constructed under the flue pan.
and another burner mounted; however, this is
not always satisfactoiy.

\ftzzh' Tip

For evaporators in which the length is ap-
proximately twice the width, the nozzle tip
should be at an 80° angle. For evaporators in
which the length is greater than twice the
width, the nozzle should be at a 60° angle.
Irrespective of the type of nozzle tip or the
angle, the burner must be adjusted so that the

PN-47S5

Figure 89. — When one large burner cannot be mounted
sufficiently far below the pan, two or more .smaller
burners can be mounted horizontally to give the re-
quired amount of heat without danger of producing hot
spots.

correct amount of air is fed along with the
atomized oil to insure complete combustion.
This can be checked with a flue gas analyzer.

Arvh

,1 (

ihiisti

( h

The arch for oil fuel also serves as a support
for the evaporator pans and contains the com-
bustion chamber and the flue for the hot gases.
The arch should be located in the evaporator
house to provide an adequate working space
with room for installing supplemental arches as
the operation is expanded. The arch need not
be in the center of the evaporator house but
may be at one side. The concrete footings for
the arch should be on gravel and should extend
below the frostline. An all-masonry arch, with
external walls built of cinder block or brick,
may be built on the site, or the arch may be
prefabricated with exterior walls of sheet metal
on a cast iron and steel frame. In either case, it
must conform to certain minimum dimensions.
The interior construction is similar for both.

Dinu-nsioiia <>/ trr/i.— The size (length and
width) of the arch is determined by the size of
the evaporator. It must be wide enough to
support the pans and long enough not only to
support the pans but also to hold the base of
the flue-gas stack. Chart 12 shows a masonry
arch for a 5- by 12- foot evaporator (9- foot flue
pan and 3- foot flat pan). The outside walls are

MAPLE SIRUP PRODUCERS MANUAL

Cinder till, may have
I" fire brick facing

Combustion chamber
Insulating fire brick
(2800° F, )

— Cinder brick

Firebrick,
zS'V X 4'/2" X 9"

LONGITUDINAL SECTION T i i T T I i CROSS SECTION

Chart ;^.— Arch and firebox for oil-fired evaporator.

cinder block except for the top section, which is
3V2-inch bricks to provide a 2-inch supporting
surface for the pans and project IV2 inches
beyond the pans. If the arch is made to the
exact outside dimensions of the pans, the sup-
porting wall of the arch would cover too much
of the underpan surface (3V2 inches on all sides).
A large loss of heating surface would result.

The height of the ai'ch is governed by the size
of the combustion chamber, which in turn is
governed by the size of the burner (see table 5)
and the size of the evaporator. For a 5- by 12-
foot evaporator, the height of the arch should
be 46 inches (chart 12). The arch should elevate
the pans 46 inches or more above the floor level
to permit the use of gravity flow of the sirup in
successive operations. If the arch raises the
pans too high, especially when multiple evapo-
rators are used, a catwalk can be installed; or
the combustion chamber of the arch and the
burner can be built in a pit.

Firebox and (.ombustioii Chamber. — The

entire open space enclosed by the arch under
the pans is the firebox. Better results will be
obtained if it contains a combustion chamber
(see chart 12). The function of this chamber is
(1) to provide a hot radiating surface and (2) to
utilize the hot, incandescent surface to vaporize
and insure complete combustion of the oil.

For maximum efficiency, the size of this com-
bustion chamber must conform to minimum
dimensions that are related to the nozzle size of
the burner. These dimensions are given in table
5. A rule-of-thumb relation between combus-
tion chamber and nozzle size is that there
should be a floor area of 90 square inches for
each gallon per hour of rated nozzle capacity.

The distance between the top of the combus-
tion chamber and the bottom of the pans (di-
mension D of chart 12) is important for two
reasons: (1) The ball of burning oil should be far
enough below the "cold" pan surface to prevent

62 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

Table 5. — Inside dimensions of combustion chamber and stack diameters

Distance
from center
burner
Burning rate of draft tube
oil (g.p.h.) to combus-
tion cham-
ber floor
(A)

Minimum
height

(B)

between
Length for nozzle combustion

angle of-

chamber
and top
of arch

(D)

(E)

Width for nozzle
angle of —

80°

Approxi- Minimum

mate floor diameter of

area stack

Inches inches

5 9 18

6 9 18

7 10 19

8 11 19

9 11.5 19

10 12 19

12 13 20

14 14 21

16 15 22

18 16 23

20 17 24

22 18 25

24 19 25

Inches Inches

25
27
29
30
32
33
36
39
41
44
47
49
51

21
23
25
26
28
29
32
35
37
40
42
44
46

Square

inches

450

540

630

720

810

900

1,080

1,260

1,440

1,620

1,800

1,980

2,160

Inches
10
10
10
12
12
12
12
14
14
16
18
20
20

corrosive deposits on the underside of the pan;
and (2) the ball of fire must be far enough below
the pan so that the acute angle of radiation
from the apex (ball of fire) to the extreme sides
of the pan is kept to a minimum (table 5). If the
ball of fire is too close to the pan, there is
insufficient space between the pans and the top
of the combustion chamber; and the angle of
radiation becomes too great. This results in
uneven heating across the width of the pan.
Overheating occurs directly over the fire. This
can be compensated for only by using more
than one burner mounted horizontally.

Construction of Arch and I'onibiistion
C.httmher

Arches may be made of sheet metal or ma-
sonry (chart 12). In arches made of either mate-
rial, the combustion chamber is free standing
within the arch and is constructed of insulating
firebrick. In sheet-metal arches the remainder
of the arch is lined with hard firebrick. The
combustion chamber is separated from the ex-
terior wall of the arch by an air space to allow
for expansion of the heated bricks. For the
same reason, there is an air space between the
hard firebrick liner and the exterior walls of the

arch. The fill between the combustion chamber
and the rear of the arch must be of a nonpack-
ing material such as cinders.

Size of Stack

Since the oil burner is operated under forced
draft, the flue stack need not be as high or as
wide as when wood is the fuel. The size of the
stack is governed by the size of the oil burner
(table 5).

With only one arch, it is recommended that a
complete evaporator, flat pan, and flue pan be
used. However, it is also recommended that the
flue pan be at least two-thirds the total length
of the evaporator. The flat pan serves as the
semifinishing pan in which the sap is raised to
a density of 55° or 60° Brix. The partly concen-
trated sap should be transferred from the evap-
orator to the finishing pan where the final
stage of evaporation is completed. Although sap
can be concentrated to sirup in the evaporator,
this practice is not advised.

Installation of Multiple Arches

To increase the capacity of the evaporator,
additional arches and pans can be added. Each
additional arch should be equipped with a flue

MAPLE SIRUP PRODUCERS MANUAL

pan only and should be installed ahead of and
in series with the complete evaporator (see
chart 13). The supplemental flue pan arches are
constructed in exactly the same manner as the
one for the complete evaporator. To connect the
supplemental flue pans in series with the evap-
orator requires only one point at which the raw
sap is fed and one point at which the partly
evaporated sap or sirup is removed for transfer
to the finishing pan or bottling tank. In the
multiple unit assembly, the flat pan of the
evaporator continues to serve as the semifinish-
ing or finishing pan (fig. 90).

Efficiency af Heat

A study of the use of oil as fuel for the
evaporation of maple sap in an open evaporator

was reported by Phillips and Homiller (87).
They showed that commercial maple sap evapo-
rators fired with oil haye an efficiency of 66 to
74 percent. Their data were obtained with a
smaller-than-average evaporator; larger evapo-
rators would be expected to be slightly more
efficient. The efficiency of the open pan evapo-
rator compares favorably with commercial
steam generating plants, for which a combus-
tion efficiency of 80 percent is considered good.
The efficiencies obtained by Strolle and oth-
ers (111) in evaporating 45 to 55 gallons of 3°-
Brix sap to standard-density sirup are given in
table 6. These data indicate that efficiency de-
creases as the rate of sap feed (gallons of sap
evaporated per hour) increases and that oil cost
per hour also increases. However, from further

Figure 90.— In one of the most economical and efficient types of evaporators, an oil fire and four fine pans are used for
evaporation; high-pressure steam is used for the last stage of evaporation.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

FLOW DIAGRAM
OF MULTIPLE UNIT EVAPORATOR

OIL
FIRED

FINISHING PAN
(GAS FIRED)

TO
POLISHING FILTER
AND CANNING TANK

Chart 13. — Flow diagram of multiple-unit evaporator.

calculations and rough extrajX)lations the data
in table 7 were obtained.

These data show that sirup production in-
creases as the amount of fuel burned increases.
The increase in cost of fuel per gallon of sirup is
slight and is more than compensated for by the
improvement in the gi-ade of the sirup and the
reduction in evaporation time and cost of labor.

Table 6. — Efficiency of oil-fired experimental
evaporator in evaporating sap of 3° Brix to
standard-density sirup

Sap evaporated per
hour (gallons)

Oil burned per
hour

Efficiency

45
50
55

Gallons
3.9

4.7
5.3

Percent
74
69
66

Table 7. — Extrapolated efficiency of oil-fired
evaporator

Sap evapo
rated per

hour
(gallons)

Cost of
Oil Sirup oil per

burned made gallon of
per hour per hour sirup
produced

Time re-
quired to
evapo-
rate 550
gallons
of sap

Effi-
ciency

Galloyis Gallons Dollars Hoiirs Percent

65 6.7

60 6.0

55 5.3

50 4.7

45 3.9

2.36 1.00 8.5 59.6

2.18 .96 9.2 62.6

2.00 .93 10.0 66

1.82 .91 11.0 69

1.64 .84 12.2 74

The maximum efficiency that could theoret-
ically be obtained from an oil-fired evaporator
would utilize all the British thermal units
(B.t.u.'s) of a gallon of oil. This heat would raise
the temperature of the feed sap to its boiling
point and then vaporize the water in the sap to
steam. Assuming that the temperature of the
sap is 35° F. and its boiling point is 210°, the
heat (B.t.u.'s) required to evaporate 34.4 gallons
of sap with a density of 2.5° Brix to yield 1
gallon of standard-density sirup can be calcu-
lated. Knowing the B.t.u.'s of No. 2 fuel oil
(139,000), the number of gallons of oil required
to produce this gallon of sirup at maximum
efficiency is 2.2 gallons. Since no oil burner is
100-percent efficient, and oil-fired evaporators
are only 60- to 75-percent efficient, the fuel
required per gallon of sirup is 3+ gallons of oil.

To measure the efficiency of burners, arches,
and evaporators, a number of factors must be
carefully obtained. These are:

MAPLE SIRUP PRODUCERS MANUAL

(1) The Brix Value of the Raw Sap.— For
example, only half as much water is evaporated
from 3°-Brix sap as from a lV2°-Brix sap to
make standard-density sirup. Therefore, other
things being equal, it would require only half as
much oil to make sirup from 3°-Brix sap as from
lV2°-Brix sap.

(2) Temperature of Sap. — The temperature of
the sap as it enters the evaporator must be
noted, since a great deal of heat is required just
to heat the sap from its storage temperature to
its boiling temperature. Therefore, the warmer
the sap, the less oil required to heat it to
boiling.

(3) The Brix Value of the Finished Sirup.— AW
too often the exact Brix value of the finished
sirup is not considered in making efficiency
studies. Yet a difference of only a few tenths of
1° in Brix value has a pronounced effect on the
number of gallons of sap that must be evapo-
rated to produce the sirup.

For cost accounting records, most producers
will find that merely to divide the number of
gallons of sirup made by the number of gallons
of oil burned will give the fuel costs per gallon
of sirup. These data should be considered an
estimate of the efficiency of the oil-burner in-
stallation.

The cost of fuel oil can be kept low by con-
tracting for it through competitive bidding. The
heat (B.t.u.'s) produced by one cord of wood is
approximately equivalent to that produced by

175 gallons of oil. The efficiency of wood de-
pends on many variables, such as condition of
the wood, size of the individual pieces, how it is
fired, condition of the fire, and stack height.

Summary'

(1) Wood

(a) Use only well-seasoned dry wood, either
cord or slab.

(b) Keep a steady fire.

(d) Keep the fire doors ojien only long enough
to charge the firebox.

(e) Ojjen the dampers and draft doors only
enough to furnish the air for combustion.

(2) Oil

(a) Oil is recommended if there is a shortage
of labor.

(b) The firebox and arch must be specially
built.

(3) Increase the capacity of the evaporator
through the addition of one or more sap or
flue pans.

(4) Mount the supplemental pans on their indi-
vidual arches.

(5) Hook up the supplemental arches in series
with the evaporator.

(6) Use a finishing pan.

MAPLE SIRUP

The characteristics of maple sirup are dis-
cussed here so that the development of color
and flavor will be better understood.

(Composition of Sap and Sirup

Table 8 gives the composition of maple sap
and sirup. The analyses in this and later tables
are not average values; they are analyses of
typical saps and sirups. Usually the sirup and
sap have essentially the same composition, ex-
cept that on an "as is" basis the constituents of
the sirup show a thirtyfcld to fiftyfold increase
as a result of concentrating the sap to sirup.
The amounts of some of the constituents, when
expressed on a dry-weight basis, are less in

sirup than in sap because of their removal from
solution as insoluble sugar sand.

The different kinds of sugar in maple sap are
not numerous (91). Sucrose, the same sugar as
in cane sugar, comprises 96 percent of the dry
matter of the sap and 99.95 percent of the total
sugar (table 9). The other 0.05 percent is com-
posed of raffinose together with three unidenti-
fied oligosaccharides. Un fermented sap does
not contain any simple or hexose sugars.

The sap contains a relatively large number of
nonvolatile organic acids (table 10), even
though they account for only a small proportion
of the solids (89). The concentration of malic
acid is 10 times that of other organic acids. If

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

Table 8. — Composition ofynaple sap and
sirup '

Sap

Sap (dry Sirup (dry
weiRlit) weight)

Percent Percent Percent

Sugars 2.000 97.0 98.0

Organic acids .030 ^1.5 .3

Ash .014 ".7 .8

Protein .008 .4 .4

Unaccounted for __ .009 .4 .5

' Typical values, not averages. Maple sap and sirup
vary in composition between rather wide limits.

Table 9. — Siigars in maple sap and sirup

Sugars

Sap

Sap (dry
weight)

Sirup (dry
weight)

Hexoses

Sucrose

Raffinose and a

Percent
_ 0
. 1.44

^ .00021

.00018
.00020
.00042

Percent

0
96.00

.014

.013
.014
.028

Percent

0-12

88-99

glycosyl sucrose _
Oligosaccharides: -
I

III

' Typical values, not averages.

■ The oligosaccharides have been isolated by chroma-
tography but have not been identified.

may prove to be useful in detecting adultera-
tion (151). One or more of these acids may be
important in forming "maple flavor." Sap con-
tains soluble ligninlike substances that are in-
volved in the formation of maple flavor (117).

The ash or mineral matter (table 11) accounts
for only 0.66 percent of the whole sirup, or 1
percent of the dry solids. Although the minerals
are only a minor part of the sirup, they have
been useful in establishing the purity of maple
sirup and they contribute an astringency to the
sirup that many find desirable.

Calcium, a part of the ash, is responsible for
the sugar-sand scale, calcium malate, which
forms on the pans (18). The low sodium and
high potassium content of the ash suggests the
use of maple in dietary foods.

Composition of sugar sand ranges as follows
U8):

Range

Sugar sand in run percent__ 0.05- 1.42

pH 6.30- 7.20

Ca percent-. 0.61-10.91

K do 0.146-0.380

Mg do 0.011-0.190

Mn do — _ 0.06- 0.29

P .... do 0.03- 1.18

Fe p.p.m... 38-1,250

Cu p.p.m._. 7- 143

B p.p.m..^ 3.4- 23

Mo p.p.m... 0.17- 2.46

Free acid percent-^ 0.07- 0.37

Total malic acid do 0.76-38.87

Acids other than malic do 0.08-2.62

Undetermined material do 6.94-34.16

Calcium malate do 1.30^9.41

Sugars in dried samples do 33.90-85.74

Sugar sand in dried samples do 14.26-66.09

Table 10. — Nonvolatile organic acids in maple
sap and sirup '

Acid

Sap

Sap (dry
weight)

Sirup (dry
weight)

Percent

0.021

.002

.0003

.000

Trace
0

Percent

1.40

.13

.02

.L«0

Trace
0

Percent
0.141

Citric

.015
.012

.006

Glycolic or

dihydroxybutyric-

Unidentified acids:

I, II, III, IV

V, VI, VII

.006

Trace
Trace

' Typical values, not

averages.

Table 11. — Mineral composition of maple
sirup '

Item

Sirup

Diy weight

Soluble ash

Insoluble ash ...

Percent

0.38

.28

Percent

0.58

.42

Total ash ...

.66

1.00

Potassium

Calcium

.26
.07

.40
.11

Silicon oxide
Manganese

.02

.005
.003

.03

.008
.005

Magnesium

Trace

' Typical values,

not averages.

MAPLE SIRUP PRODUCERS MANUAL

The nitrogenous matter constitutes only a
small part of the total solids (88).'' Expressed as
nitrogen, the sap contains only 0.0013 percent
and the sirup 0.06 percent. The sap does not
contain any free amino acids except late in the
sap-flow season. Nitrogen occurs only in the
form of peptides. Whether the nitrogenous mat-
ter enters into the formation of maple color or
flavor is an open question. An increase in free
amino acids is associated with the development
of "buddy sap."

FORMATION OF TRIOSES
FROM SUCROSE

HYDROLYSIS OF SUCROSE

C|2 HjjO,,
(SUCROSE)

FISSION OF HEXOSES

(HEXOSES)
► Cg HiaOe + CsHjOg
(GLUCOSE) (FRUCTOSE)

(.olor anti Flavor

Maple sap as it comes from the tree is a
sterile, ciystal-clear liquid with a sweet taste.
None of the brown color or flavor that we
associate with maple sirup is in the sap. This is
easily demonstrated by collecting sap asepti-
cally, freezing it, and then freeze-drying it. The
solid obtained is white or very light yellow and
has only a sweet taste. The typical color and
flavor of maple sirup are the result of chemical
reactions, involving certain substances in the
sap, brought about by heat as the sap boils
(H8). Since at least one of the products of the
reaction is the brown color, it is known as a
browning reaction. Neither the exact nature of
this reaction nor the identity of the reacting
substances is known. Indications are that one
or more of the 6 sugars or their degradation
products and one or more of the 12 organic
acids in maple sap are involved in the browning
reaction.

Experimental evidence indicates that the
color and flavor of maple sirup are related to
triose sugar {52-5J,, 118-120, 122, 155). These
sugars are not constituents of sap when it
comes from the tree but are formed as a result
of the two reactions shown in chart 14. Evi-
dence also indicates that the phenolic ligninlike
substances of maple sap are intermediate in the
flavor reactions and may account for the speci-
ficity of maple flavor (117).

The amount of invert hexose sugars is di-
rectly proportional to the amount of fermenta-
tion that has occurred. The first reaction is the
bacterial or enzymatic hydrolysis of the sucrose
to form invert sugar, a mixture of fructose and

GUUCIC ACID

TRIOSE n

ACETOL

'Also unpublished data of Eastern Regional Research
Center.

Chart li. — Chemical reactions showing the formation of
trioses from the sucrose of sap. In the first reaction, 1
molecule of sucrose is hydrolyzed by enzymes to yield 2
molecules of hexose sugars. In the second reaction,
these hexoses are broken by alkaline fission into
trioses.

dextrose (chart 14). The second reaction is the
alkaline degradation of the fructose and dex-
trose to trioses (98). The second reaction occurs
while the sap is boiling in the sap pan, where
the alkalinity of the sap reaches a pH of 8 to 9.
These trioses are highly active chemically.
They can combine with themselves to form
color compounds, and they can react with other
substances in the sap (such as organic acids) to
form the maple flavor substances (79).

Experiments have established that up to a
point the amount of color formed is proportional
to the amount of flavor formed. This makes it
possible to evaluate flavor in terms of color, a
measurable quantity. When the point is
reached at which the background flavor "cara-
mel" begins to be noticeable, this relation no
longer holds.

The identity of the compounds responsible for
the flavor of maple has proved to be elusive.
Certainly all the components of maple sirup

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

contribute to its flavor — the sugar, the organ it-
acid salts, and even the oil, butter, or whatever
was used as an antifoam agent during evapora-
tion. An unknown number of trace materials in
the sirup or sugar give it "maple flavor." These
compounds have defied identification for many
years because they exist in very small amounts
(a few parts per million), and their chemical
character in many cases is so similar to carbo-
hydrates that separation from the sugars of the
sirup has been extremely difficult (123). Now
with the modern techniques of gas chromatog-
raphy and mass spectrometry, progress is being
made in solving the mystery of "maple flavor."
The flavor compounds identified can be divided
into two groups according to their probable
source. One group, possibly formed from lig-
neous material in the sap, contains such com-
pounds as vanillin, syringealdehyde, dihydro-
coniferyl alcohol, acetovanillone, ethylvanillin.
and guaiacyl acetone. A second group, most
likely formed by caramelization of the carbohy-
drates in the sap, includes acetol, methylcyclo-
pentenolone (cyclotene), furfural, hydroxymeth-
ylfurfural, isomaltol, and alpha-furonone (25,
116). It has been impossible to make a synthetic
maple flavor by combining these compounds.
Perhaps one or more key compounds have not
yet been identified. Even if all these compounds
were available, a proper balance of the many
parts of a mixture to give the desired combina-
tion flavor would be difficult to achieve since
they have not been accurately measured.

Factors that control color and flavor are: (1)
Amount of fermentation products in the sap
(75)\ (2) pH of the boiling sap; (3) concentration
of the solids (sugars); (4) time of heating (time
necessary to evaporate sap to sirup); and (5)
temperature of the boiling sap (la, 150). The
two most important factors are the time of
heating and the amount of fermentation prod-
ucts in the sap (150). The temperature of the
sap under atmospheric pressure (open pan) boil-
ing is fixed, and nothing can be done about it.
Neither can anything be done about changes in
pH of the boiling sap. At the beginning of
evaporation, the natural acidity of fresh sap is
lost and the sap becomes alkaline. It is during
this alkaline phase of the pH cycle that hexose
sugars, if any are present, undergo alkaline
degi-adations. The sap then remains alkaline

until sufficient organic acids are formed by the
decomposition of the sap sugars to make the
sap acid again.

The longer the boiling time, the darker the
sirup; and, conversely, the shorter the boiling
time, the lighter the sirup. During evaporation,
the effect of the boiling-point factor increases
as the solids concentration of the sap increases.
The relation between the amount of hexose
sugars (invert sugar) produced during the fer-
mentation of the sap and the length of time the
sap is boiled is of the greatest importance.
Thus, the color and flavor of sirup made in
exactly the same boiling time from a series of
saps of equal solids concentration (Brix value)
but with increasing amounts of invert sugar
will be progressively darker and stronger. The
stronger maple flavor, however, is usually
masked by the acrid caramel flavor. Although
flavor and color are formed because of exo-
thermic chemical reactions, the amount of fla-
vor that can be produced is limited by the
concentration of the sap-soluble lignaceouslike
materials that are probable flavor precursors.
Indications are that there are sufficient of
these flavor percursors in sap to permit forming
a product that is from 15 to 30 times richer in
maple flavor than is commercial "pure maple
sirup" (15i). These precursors can be utilized to
increase the flavor by subjecting the sirup to
higher temperatures. This method is used in
preparing high-flavored maple products, de-
scribed later.

Buddy Sap and Sirup

As the maple tree comes out of dormancy,
physiological changes in the tree form constitu-
ents in the sap which, when boiled, give off a
noxious odor and impart a characteristic, un-
pleasant flavor to the sirup. This noxious odor
is most noticeable in sap obtained from trees
whose buds have swelled or burst during a
period of warm weather; and sirup made from
this sap is said to have buddy flavor. Due to the
unseasonably warm weather in 1963, buddy sap
was produced early in the sap season. Because
of this, much of the crop was not harvested in
some areas. Although the trees may not have
come far enough out of dormancy to cause the
buds to swell, they may have come out enough

MAPLE SIRUP PRODUCERS MANUAL

to produce the unwanted flavor. The formation
of this buddy substance is accompanied by an
increase in the free amino acids in the sap.
Whether this parallel increase in free amino
acids is involved in the foi-mation of buddy
flavor remains to be determined.

Often some trees in a sugar grove "bud"
earlier than the rest. These trees should be
identified and marked so that their sap will not
be collected late in the season. To combine the
sap from trees that have budded with that from
the other trees would spoil the entire lot of late-
season sap.

The practice of treating the taphole with
germicidal wllets will cause the sap to flow late
in the season and when the tree is far enough
out of dormancy so that the sap is buddy.
Test for Buddy Fhivor

It is essential that sap produced during or
following a warm spell or from trees whose
buds have swelled be tested for buddiness

The best and simplest test is easily performed
by bringing V4 cup of the sap or sirup to be
tested to a boil and sniffing the steam. If the
buddy flavor substances are present, they can
be detected in the steam. The sap or sirup can
be heated with an electric immersion-type
heater used for making instant coffee. This test
is subjective, and the buddy odor may not be
strong enough to be easily recognized by some
people.

Another test that is applicable to sirup and
not subjective has therefore been developed.
This test involves the chemical test for amino
acid groups whose presence in sap parallels
buddy flavor formation (115).

To make the test the following equipment is
needed:

A 1-ounce (30 ml.) screw-cap bottle to hold the
standard amino niti'ogen solution.

A box of wooden toothpicks.

Test papers — filter paper cut into ^/a- x 4- inch
strips.

The following reagents should be used:

Standard amino nitrogen solution. This is
made by dissolving .5 grams of leucine (an
amino acid) in 30 milliliters of water.
(Place 1 level teaspoon of leucine in the 1-
ounce bottle and fill it to the neck with
water.)

Ninhydrin spray. This is commercially availa-
ble as an aerosol spray.
The test should be made as follows:

(1) To a small volume of the sirup to be te.sted,
add an equal volume of water and mix thor-
oughly.

(2) With a pencil make three dots 1 inch apart
down the center of the test strip, 1 inch from
either end. Label X, S, and W.

(3) Holding a toothpick in a vertical position,
dip the broad end into the diluted sirup and
transfer a drop to the pencil dot at the top of
the paper labeled X.

(4) Using fresh toothpicks, transfer a drop of
the standard amino nitrogen solution to the dot
at the center of the paper labeled S, and a drop
of water to the dot at the bottom labeled W. The
size of the wetted spots should be about the
same.

(5) Lay the paper on a clean, diy surface
(piece of filter paper) and allow the spots to dry
at room temperature.

(6) Spray the entire paper strip with the
ninhydrin reagent. Wet the paper thoroughly
but not enough to cause the reagent to run.

(7) Dry the sprayed paper at room tempera-
ture.

(8) Heat the paper at a temperatui-e of 175° to
195° F. for approximately 1 minute to hasten
development of the color. The lid of a boiling
kettle or other moderately hot surface will suf-
fice. (From 1 to 2 hours will be required for the
color to develop at room temperature.)

(9) Development of a violet color constitutes a
positive test and indicates that the sap is
buddy.

The standard amino nitrogen solution is used
to indicate that the ninhydi-in reagent is react-
ing properly to give violet color with amino
compounds.

Ninhydrin reagent is a very sensitive stain.
Care must be taken to keep the paper test
strips clean. Handling the test strip with for-
ceps, especially after staining, will prevent fin-
gerprints which could produce false-colored
spots. The papers are best sprayed by hanging
them in an open cardboard box to prevent
discoloration of other objects by the ninhydrin
spray. The ninhydrin i-eagent is not stable and
should be replaced at least every 6 months.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

Always start with a fresh supply of the reagent
at the beginning of each sirup season.

Rcrlaiininff Buddy Sirup and Sap

Many sirupmakers make buddy sirup from
the late runs of sap. Although this practice
should not be encouraged because of the very
low price commanded by buddy sirup, it is
made — often unknowingly. ^

Buddy sap and buddy sirup can be treated by
a fermentation procedure to remove their un-
palatable flavor {136, 137). Because this process
requires special equipment and a high degree of
technical conti'ol, it has not been commercially
successful. Recently a new procedure has been
developed using ion-exchange resins to remove
the buddy off- flavor (36a). This process removes
the amino acids believed to be responsible for
the buddy flavor of maple sirup. The cost of this
treatment on a commercial scale is estimated to
be less than $1 per gallon of sirup.

Riilo of Sirupinakin^

The following rules should be followed in
sirupmaking:

(1) If possible, test all sap for buddiness; but
especially test that produced late in the spring
or following a warm spell. Do not use buddy
sap.

(2) Do not use fermented sap. To keep the sap
from fermenting, collect it often. Do not allow it
to stand in the buckets or tanks, and keep it
cold. If there is a small flow of sap that does not
warrant collecting, dump it. At least once dur-
ing the season, wash the sap-gathering equip-
ment (buckets, pails, and tanks) and sanitize
the equipment with a 10-percent hypochlorite
solution.

(3) Handle the sap as quickly as possible. The
sooner sap is evaporated after it has been
obtained from the tree, the higher the grade
and the lighter the sirup that will be produced.
The faster sap is evaporated to sirup, especially
during the last stages of evaporation when the
solids concentration is highest, the lighter the
color and the higher the grade of the sirup.

(4) Keep sap and equipment clean. Cleanli-
ness is a must in maple sirupmaking for, aside
from its esthetic aspects, cleanliness is the only
way to control microbial contamination and

subsequent growth in the sap. Sirup made from
sap in which growth of micro-organisms has
occurred tends to be dark colored and low in
grade.

(5) By means of a hydrometer or other suita-
ble instrument, measure and record the sugar
content of the sap produced by each tree and
also the sugar content of each batch of sap in
the storage tanks.

(6) Store sap in a cool place.

(7) Store sap in tanks exposed to daylight (not
necessarily direct sunlight).

(8) Cover the tanks with material transparent
to ultraviolet radiation, such as clear plastic.

(9) Provide tanks having opaque covers with
germicidal lamps.

Grades of Sirup

It is generally believed that the best sirup is
made early in the season during the first and
second runs of sap. However, this is not neces-
sarily true, as was demonstrated in 1954 when
sirup made early in the season was darker than
some made later. The important factor is the
atmospheric temperature. Warm weather favors
microbial growth, and the byproduct of this
growth — invert sugar — affects the color and
grade of the sirup. It is only coincidental that
the weather is usually cooler at the beginning
of the season and microbial growth is low.

Sap that is essentially sterile contains very
little invert sugar and will usually produce a
light-colored, light-flavored, fancy sirup. Some-
times, as in 1954, the weather at the onset of
the season is warm, and fermentation occurs.
The result is that the first-run sirup is darker
than expected. If conditions are reversed later
in the season, fancy sirup will be produced, for
with cold weather little or no fermentation of
the sap occurs.

Making light-colored sirup with sterile sap
that is veiy low in invert sugar does not test a
sirupmaker's skill. However, skill is required to
produce light-colored sirup from sap rich in
invert sugar (with a high microbial count). This
skill is actually a measure of how fast the
sirupmaker can evaporate the sap to sirup.

Sirup can be darkened — changed from U.S.
Fancy to U.S. Grade A, or from U.S. Grade A to
U.S. Grade B, etc.— by prolonging the heating

MAPLE SIRUP PRODUCERS MANUAL

of the finished sirup. If a finishing pan is used,
it should be covered immediately when the
sirup reaches the correct density. The heat
should be reduced to maintain a slow boil until
the desired color is obtained. Adding V2 cupful
of U.S. Grade C sirup for every 2 gallons of sap
will hasten the darkening process.

SuiTunar\

(1) Maple sap and sirup contain only sugar,
protein, organic acids, ash, and less than 2
percent of material not accounted for but
which is of great importance because it
includes the color and the flavor substances.

(2) Sterile maple sap has neither color nor fla-
vor.

(3) Experimental evidence indicates that the
color and flavor in maple sirup are related
to triose sugars, organic acids, and soluble,
ligninlike substances.

(4) Factors controlling the formation of color
and flavor include fermentation, pH, solids
concentration, length of boiling time, and
the boiling temperature of the sap.

(5) The shorter the boiling time, irrespective of
the quality of the sap, the lighter the color
of sirup produced.

(6) For best sirup —

(a) Use sap that has not fermented.

(b) Use speed in collecting and in evapo-
rating the sap.

(d) Know the initial Brix value of the
sap.

(7) Higher grades of sirup are usually produced
earlier in the season than later on, because
the early season temperatures are usually
lower and there is less chance of fermenta-
tion.

(8) Sirup that is too light can be darkened by
heating the finished sirup.

CONTROL OF FINISFIED SIRUP

Finishing the sirup is one of the most exact-
ing tasks in maple sirupmaking. The sirup must
be drawn from the evaporator or finishing pan
at just the right instant; otherwise, its solids
content (density) will be either too high or too
low. To conform with minimum Federal and
State requirements, sirup must have a density
of not less than 66.0° Brix at a temperature of
68° F. At this density, a little more or a little
less evaporation has a relatively large effect on
the concentration (table 12). Hence, when using
large evaporators capable of evaporating sev-
eral hundreds of gallons of water per hour,
accurate control of the sirup being drawn off is
both important and exacting.

Viscosity of Maple Sii-up

Maple sirup having a density of only 0.5° to 1°
Brix below standard-density sirup tastes' thin.
This is due to the big change in the viscosity of
sugar solutions caused by only a slight change
in concentration, especially in the range of
standard-density sirup.

Table 13 shows that an increase in the sugar
concentration of sucrose solutions up to 30°
Brix has little effect on viscosity. For example.

a solution with a density of 20° Brix at room
temperature (68° F.) has a viscosity of 2.3 centi-
poises and at 30° Brix only 3.2 centipoises.
However, as the concentration of the sugar
increases, the viscosity increases at an ex-
tremely rapid rate. Thus, to treble the sugar
concentration from 20° to 60° Brix increases the
viscosity from 2.3 to 44 centipoises — more than
a nineteenfold increase.

The change in viscosity is even more pro-
nounced in sucrose solutions with densities in
the range of standard sirup (66.0° Brix).

As shown in the table, the viscosity of sirup
at room temperature (68° F.) is lowered 34.8
centipoises if its density is 1° Brix below stand-
ard density. It is lowered 61.9 centipoises if it is
2° Brix below standard density. The lowered
viscosity has a marked adverse effect on the
keeping quality of the sirup and on its accept-
ance by consumers. The tongue is extremely
sensitive to these differences.

The tongue is also sensitive to slight in-
creases in the density of sirup above 66.0° Brix
at room temperature. An increase of only 1°
Brix above standard density increases the vis-
cosity of sirup 45.8 centipoises; and the sirup
acquires a thick, pleasant feel to the tongue.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

Table 12. — Boiling temperature above that for
water for solutions of different concentrations
of sugar

Temperature
elevation, ° F

Sugar
solutions

Temperature
elevation, ° F.

Sugar

.solutions

0.0

Percent
0.0
7.5

13.8

19.0

23.4

27.1
30.3
33.4
36.0
38.4

40.5
42.5
44.3
46.0

47.7

49.0
50.4
51.6
52.8
53.9

54.9
55.9
56.9

57.8
58.8

5.0
5.2
5.5
5.6
5.8

5.9 .
6.1 .

6.4 .
6.6 .
6.9 .

7.1 .
7.3 .

7.5 .

8.0 .

8.2 .

8.5 .

8.8 .

9.1 _
9.5 _

9.9 _

10.4 _
10.7 .
11.1 _

11.5 _

12.0 _

Percent
59.7

0.2

60 4

0.4

61.5

0.6

62 0

0.8

62.5

1.0

62 9

1.2

63.4

1.4

64.4

1.6

64 9

1.8

65 6

2.0

66 0

2.2

66.5

2.4

67 0

2.6

68 0

2.8

68 5

3.0

69 0

3.2

69 5

3.4

70 0

3.6

70.5

3.8

71 0

4.0

71.6

4.2

72 1

4.4

72.5

4.6

73 0

4.8

73 5

Thus, the thicker the sirup, the better it tastes.
However, sirup with a density of more than 67°
Brix crystallizes on storage at room tempera-
ture; 67° Brix, therefore, becomes the upper
permissible density.

EfTect orTemiMM-atiiiT on N iscosily

As the temperature of a sugar solution in-
creases, its viscosity drops sharply. Standard-
density sirup at its boiling point has a viscosity
of about 6 centipoises, which is only one.thir-
tieth that of sirup at room temperature; that is
why sirup filters so much better when it is at or
near its boiling point. Likewise, the viscosity of
boiling sirup with a density between 50° and 60°
Brix is approximately one-half that of stand-
ard-density sirup; and that is why it is advanta-

geous to filter sirup just before it is transferred
to a finishing pan, when its density is approxi-
mately 60° Brix or less.

This lowering of the density by heating sirup
explains why hot sirup, even though it is of
standard density, tastes thin and watery.

Old Stan(iar<l»; <)f FinLshed .Sirup

In the past, the finishing point of sirup was
determined by a number of methods. None of
these methods was precise, and their skillful
use was an art. For that reason, comparatively
few men won the enviable title of "sugar-
maker."

Typical of these methods was the "blow" test.
In this test, a small loop of wire was dipped into
the boiling sap. When the film that formed
across the loop required a certain puff of breath
to blow it off, the sirup was considered finished.
Another method more commonly used was the
"apron" test. In this test, a scoop was dipped
into the boiling sap and then held in an upright
position to drain. Formation of a large, thin
sheet or apron with the right shajDe and other
characteristics indicated that the sirup was
finished.

L M- ol' \*vvvisiou lii.sti-iini('iil!<

Precision instruments are now available by
which the finishing point of sirup can be deter-
mined easily and with a high degi-ee of accu-
racy. As concentration progresses, there is a
progressive increase in the boiling point, in
density, and in refractive index. These can be
measured accurately and precisely with a ther-
mometer, a hydrometer, and a refractometer,
respectively. However, only the elevation of the
boiling point is applicable to a sugar-water
solution, such as sap, while it is actively boiling.

Kl^'^alion ol' B4Mliii<>: I'oinI

Chart 15 and table 12 show the changes in
boiling-point temperature for sugar solutions at
different concentrations. When a sugar solution
has been evaporated to the concentration of
standard-density sirup (66.0° percent of sugar,
or 66.0° Brix), its boiling point has been ele-
vated 7.1° F. above the boiling point of water.
Between 0° and 2T Brix, there is only a slight

MAPLE SIRUP PRODUCERS MANUAL

0 20 40 60
SUCROSE CONCENTRATION (PERCENT)

Chart 15. — Curve showing the relation between the con-
centration of a sugar solution (sap) and the elevation of
its boiling point above the boiling point of water.

elevation in boiling point. However, as the solu-
tion neai's the concentration of standard-den-
sity sirup, a change of only 2.5 percent in sugar
concentration (from 64.5° to 67° Brix) raises the
boiling point 1°. Hence, the boiling point method
of measuring sugar concentrations is ideally
suited to sirupmaking.

Any Fahrenheit thermometer calibrated in
degree or half-degree intervals and with a
range that includes 225° F. can be used. For
greatest usefulness and accuracy, the distances
between degree lines should be as open as
possible and should be calibrated in one-fourth
degrees.

Elevation of the boiling point as used hei'e
means the increase in temperature (° F.) of the
boiling point of the sugar solution above the
temperature of boiling pure water. It has noth-
ing to do with the specific temperatui'e 212° F.
except when the barometric pressure is 760
millimeters of merciu'v. Under actual condi-

tions of sirupmaking, the barometric pressure
is seldom at 760 millimeters; therefore, it is best
not to associate the fixed value of 212° F. with
the boiling point of water.

The recommended procedure is to establish
the temperature of boiling water on the day
and at the place sirup is being made. To do this,
merely heat water to boiling, insert the bulb of
a liquid stem thermometer or the stem of a dial
thermometer, and note the temperature while
the water is actually boiling. This is the true
temperature of boiling water for the barometric
pressure at that time and place. In practice, the
boiling sap in the sap pan can be used to
establish the temperature of boiling water
since, as was shown in chart 15, at low-solids
concentrations (up to 10° BrLx) there is little
elevation of the boiling point. The boiling tem-
perature of standard-density sirup is then
found by adding 7° to the temperature of the
boiling sap.

It is of the greatest importance to redeter-
mine the temperature of boiling water (sap) at
least once and preferably several times each
day, especially if the barometer is changing. A
change in the weather usually indicates a
change in barometric pressure. The result of
failure to making frequent checks on the boiling
point of water is illustrated in the following
examples:

On March 1, at Gouverneur, N.Y., the boiling
point of water was determined to be 210° F.,
which established the boiling point of standard-
density sirup as 217°. On March 2, the producer
neglected to redetermine the boiling point of
water, assuming it to be unchanged, and con-
tinued to use 217" as the boiling point of sirup.
Actually, the barometric pressure had fallen,
which lowered the boiling point of water to 208°
and of standard-density sirup to 215°. The sir-
upmaker, by using the temperature of 217°,
was boiling his sirup 2° too high, and the sirup
contained 69.8 percent of solids instead of 65.8
percent (table 12). This high-density sirup re-
sulted in the production of fewer gallons of
sirup; and, in addition, the sirup crystallized in
storage, since it was above 67° Brix.

If, on the other hand, the reverse had oc-
curred, the sirupmaker would have made sirup
with a boiling point 2° F. too low. This sirup
would contain only 59.7 percent of solids as

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

Table 13. — Viscosity of sucrose solutions of various densities (° Brix) at temperatures of 20° C. (68°

F.)tol05° C. {221° F.y

Density
solution
;° Brix)

Viscosity (centipoises) at —

(

20° C.
(68° F.)

30° C.

(86° F.)

40PC.
(104; F.)

50° C.
(122° F.)

60° C.
(140° F.)

70° C. 80° C.
(158° F.) (176° F.)

90° C.2
(194° F.)

100° C- 103.5° C.2 105° C.=
(212° F.) (218.3° F.) (221° F.)

20
30

2.3

3.2

15.3

44.0

69.2

_ 82.4
. 99.1
. 120.1
_ 147.2

. 182.0

. 227.8
. 288.5
_ 370.1
. 481.6

1.5

2.4

10.1

33.8

39.3

46.0
54.3
64.5

77.3

93.5

114.1
140.7
175.6
221.6

^1.2

1.8

7.0

21.0

24.1

27.8
32.3
37.7
44.4

52.6

62.9

76.0

92.6

114.0

1.0

1.5

5.0

14.0

15.8

17.9
20.5
23.7

27.5

32.1

37.7
44.7
53.3
64.4

0.8
1.2
3.8
9.7
10.9

12.2

13.8
15.7
17.9

20.6

19.4
22.6
26.3
31.0

0.7
1.0
2.9
7.0
7.6

8.6

9.7

10.9

12.4

14.1

16.1

18.4
21.4
25.0

0.6
.9
2.3
5.2
5.7

6.4
7.1
7.9
8.8

9.9

11.3
12.8
14.7
16.8

50
60
61

62
63
64
65

1.8
4.4
4.7

5.0
5.6
6.3
7.0

7.8

1.6
3.6
3.8

4.1
4.6
5.1

5.8

6.6

1.5
3.4
3.6

3.9
4.3
4.8
5.4

6.2

1.5
3.4
3.5

3.8
4.2
4.7
5.3

6.1

' Based on data from Circular C440 issued by the National Bureau of Standards, U.S. Department of Commerce, July
31. 1958.

' Values obtained by extrapolation.

sugar. It would not meet specifications for
standard-density sirup, would tend to spoil eas-
ily, and would have a low viscosity and there-
fore would taste watery.

Therefore, with a good indicator to detect the
end point of evaporation (thermometer cali-
brated in V4° F.), together with the slowdown in
rate of evaporation, as shown in chart 16, the
sirupmaker is able to stop evaporation precisely
at the desired concentration. He can do this
either by drawing off the sirup from the evapo-
rator or, if he uses a finishing pan, by turning
off the heat.

Finishing Pan

When a finishing pan is used, it is necessary
to know when the sap has been concentrated
enough to be transferred from the evaporator
to the finishing pan. This can be determined by
measuring the elevation of the boiling point of
the partly concentrated sap. Table 12 shows the
elevation of the boiling temperature of sugar
solutions (above that for water) for concentra-
tions from 0° to 73.5° Brix.

To use the table, determine the boiling tem-
perature of pure water and then observe the

boiling temperature of the partly evaporated
sap. The difference between the two boiling
points represents the elevation in boiling tem-
perature.

Two examples of how to select a boiling point
elevation to give sirup of a desired density
(° Brix) follow:

Example 1. A producer wants to draw off
sirup from the evaporator at about 40° Brix. At
what boiling temperature should the sirup be
removed if water boils at 210° F.?

Table 12 shows that the boiling temperature
is elevated 2.0° F. for solutions having a density
of 40.5° Brix. Thus, when the boiling tempera-
ture rises to 212° F. (210° + 2°), the sap will be
concentrated to approximately 40° Brix.

Example 2. A producer wants to concentrate
the sap to 50° Brix in the evaporator before
transferring it to the finishing pan. At what
boiling temperature should the sirup be drawn
off if water boils at 211.5° F.?

Table 12 shows that for solutions having a
density of 50.4° Brix, the boiling temperature is
3.2° F. above the boiling point of water. Thus,
211.5° + 3.2°, or 214.7°, is the boiling tempera-
ture of 50° Brix sirup.

MAPLE SIRUP PRODUCERS MANUAL

20 30 40 50

BRIX (DEGREES)

Chart 16. — Change in the rate of loss of water by evapora-
tion, with constant heat, as the concentration of sap
increases. Boiling sap with an initial density of 22° Brix
loses 42 grams of water per minute, whereas sirup with
a density of 65° loses only 15 grams of water per
minute, a threefold decrease in rate.

Special Theniionietei*s

In sirupmaking, a knowledge of the boiling
point of standard-density sirup in ° F. is impor-
tant provided a temperature reference point
(the boiling point of water) is established and
the correct boiling point of sirup is located 7
above it. On this basis, special thermometei's
have been developed for use in making sirup:
The liquid-stem thermometer with movable tar-
get, the liquid-stem industrial thermometer,
and the dial thermometer with movable dial.

Target Tlierntonieter

The target thermometer does not have any
markings on the stem. The degree lines on a
movable target refer to the boiling point of
water rather than to ° F., as on the conven-
tional Fahrenheit thermometei-.

The target thermometer is calibrated by plac-
ing the bulb in either boiling water or boiling
sap. The target is moved by means of an adjust-
ing screw until the line "water boils" coincides
with the top of the mercury column. The line
"sirup" is exactly 7° above the line "water
boils." This is the boiling point of standard-
density sirup for that hour and place. After
adjustment, the thermometer is placed in the
sirup pan adjacent to the place where the
sirup is drawn off.

Unfortunately, any thermometer set in the
evaporator will be surrounded by steam, which
makes it difficult to read (fig. 91).

Use of a flashlight' to illuminate the ther-
mometer and a large funnel to divert the steam
makes viewing easier. The funnel is held with
the tip toward the thermometer, and the ther-
mometer is viewed through the funnel with the
aid of the flashlight.

Liqiiitl-Slrm Inthistrial Thcriiiomflfr

The liquid-stem industrial thermometer does
not have special markings or a movable target.
But it does have an open scale — a lineal dis-
tance of approximately 3 inches for 10° F.,
which is almost three times that of other ther-
mometers (fig. 92). It is calibrated in hU" and has
a magnifying device. These features make it
ideal for use in sirupmaking. These thermome-

PN-4787

Figure 91.— The target thermometer is placed in the
boiling sirup. The fine mercury column is difficult to
see because of the steam. The boiling sirup being tested
must be deep enough to cover the bulb of the thermom-
eter. The thermometer must be in boiling sirup and as
close to the point of sirup drawoff as possible.

AGRICULTURE HANDBOOK i:{4, U.S. DEPT. OF AGRICULTURE

PN-4788

Figure 92. — The liquid-stem industrial thermometer has
an open scale that permits calibration marks for each
''4° F. and the temperature of the boiling sirup can be
measured precisely. The thermometer is mounted out-
side the pan so it is not obscured by steam. It is
especially suited when the pan is covered with a tight
steam hood.

ters can be obtained with the stem bent at
right angles and protected with metal armor.

The right-angle thermometer is mounted
through the wall of the sirup or finishing pan
using a special fitting. This arrangement per-
mits the thermometer to be mounted high
enough on the sidewall of the evaporator or
finishing pan to be above the level of the sirup
so that the thermometer can be removed for
cleaning without loss of sirup. It also locates
the scale of the thermometer at an obtuse
angle for easy reading.

The thermometer is calibrated each day in
terms of the boiling point of water. The bulb is
immersed in water, the water is brought to a
boil, and the temperature is noted. To this
observed temperature is added 7°, the tempera-
ture elevation required to give the boiling point
of standard-density sirup (see table 12).

Dial Thermomt'tt'r

The degi'ee lines of the dial thermometer (25),
like the target thermometer, refer to the boiling
point of water (fig. 93). This thermometer has a
bimetallic element in the first 3 or 4 inches of
the stem. As the indicator is a needle, the
openness of scale is governed by the length of
the needle and the accuracy required. The scale
is twice as open in a dial thermometer 5 inches
in diameter as in the target thermometer.

The dial thermometer is calibrated by im-
mersing the part of its stem that contains the
bimetallic element in boiling water or sap the
same distance that it is immersed in the sirup;
when the indicating needle comes to rest, the
dial is rotated by means of an adjusting screw
until the zero or water boils line coincides with
the pointer. Then the sirup line is located T F.
above the zero or water boils line to indicate
the boiling temperature of standard-density
sirup for that day and place.

The long straight stem of this thermometer is
inserted through the wall of the sirup pan and
sirup drawoff box so it will be parallel to the
bottom of the pan and entirely immersed in the
boiling sirup. The dial of the thermometer is on
the outside of the evaporator where it is out of
the steam and is easy to read (fig. 93).

Hydixjnietei'S

A hydrometer is not the ideal instrument for
judging the finishing point of sirup. It is not
calibrated for use at the temperature of boiling
sirup, and it cannot be used to follow the
concentration of the sap continuously. For ac-
curacy, the exact temperature of the sirup
being tested with the hydrometer must be
known so that the necessary corrections can be
made. However, the hydrometer and refractom-
eter are the only instruments that can be used
to measure the density of sirup that is not in an
actively boiling state.

•Hot Test'

The "hot test" is often used to determine
whether the process of evaporating sap to sirup
is completed. It is made as follows:

MAPLE SIRUP PRODUCERS MANUAL

PN-4789

Figure 93. — The dial thermometer, like the tai'get ther-
mometer, has markings to indicate O, water boils,
sirup, soft tub, and cake sugar. The dial thermometer,
like the industrial thermometer, is mounted on the
outside of the evaporator.

PN-4790

Figure 94. — Sirup at approximately 210° F. is used in
making the hot test. The hydrometer cup is raised to
eye level and the reading is made as soon as the
hydrometer comes to rest.

Fill the hydrometer cup with boiling sirup
from the evaporator or finishing pan (fig. 94).
Immediately place the hydrometer in the sirup
and, as soon as the hydrometer comes to rest,
make the observed density reading. Perform all
operations as quickly as possible. If the ob-
served hydrometer reading is between 59.3° and
59.6° Brix, the evaporation of the sap to stand-
ard-density sirup is completed.

For best results with the hot test, the tem-
perature of the hot sirup must be between 210°
and 218" F. at the moment the hydrometer
reading is made. To be sure that the sirup is in
this temperature range, first determine the
temperature of the hot sirup as follows:

Fill the hydrometer cup with boiling sirup.
Place the hydrometer and the thermometer in
the sirup. Then, instead of i-eading the hydrom-
eter, measure the temperature as soon as the
hydrometer comes to rest. Repeat this proce-
dure and, if the two consecutive temperature

readings are not obtained in the range of 210°
to 218' F., speed up the operation until these
temperatures are obtained at the time hydrom-
eter readings are made.

The hot test is not a precise measurement. It
is extremely difficult to make accurate hydrom-
eter and temperature readings at the same
time in sirup that is hotter than 180° F. because
the sirup is cooling rapidly.

Fi-om the time the hydrometer cup is filled
with boiling sirup until the observed hydrome-
ter reading is made, the sirup will have cooled
several degi-ees. The amount of cooling depends
on the time involved and the temperature of
the air surroimding the hydrometer cup.

Hydrothcrin

The hydrotherm, a special hydrometer (chart
17), has a liquid thermometer built into it that
automatically locates the point on the hydrome-
ter (top of thermometer liquid column) for

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

measuring standard-density sirup. The accu-
racy of this instrument depends on the relation
of Uneal expansion of the thermometer Hquid to
Hneal displacement of the hydrometer stem by
standard-density sirup at different tempera-
tures. When used, sufficient time must be al-
lowed for the thermometer of the hydrotherm
to warm or cool to the temperature of the sirup,
usually about 30 to 40 seconds.

Since the hydrotherm is not calibrated, the
scale does not indicate how much too dense or
too thin the sirup is.

Suinmarv

(1) Finished sirup must contain not less than
66.0 percent of solids (66.0" Brix) at a tem-
perature of 68° F.

(2) Table sirup that is between 66° and 67° Brix
has the best taste. Table sirup that is below
standard density tastes thin.

(3) Use precision instruments to measure
standard-density sirup.

(4) The boiling temperature of standard-den-
sity sirup is T F. above the temperature of
boiling water.

(.5) Use a thermometer calibrated in V4° F. to
measure the temperature of boiling sirup.

(6) Calibrate the thermometer frequently with
reference to the boiling point of water.

(7) Completely immerse in the boiling water or
sap the bulb of the stem of a liquid ther-
mometer or that part of the stem of a dial
thermometer containing the bimetallic ele-
ment.

(8) To test hot sirup with a hydrometer, the
temperature of the sirup must be noted and
necessary temperature corrections applied
to the observed hydrometer readings. Hot
sirup (210° to 218' F.) of standard density is
59. y to 59.6° Brix.

(9) To test hot sirup with a hydrotherm, suffi-
cient time must be allowed for the hydro-
therm to come to the same temperature as
the sirup in which it is floated.

STANDARD

DENSITY

SIRUP

THERMOMETER

Chart 17. — Hydrotherm for measuring density of sirup. It
automatically compensates for temperature correction.

(;L\RIFK:ATlo^ ok SIRl I'

Snjjar Sainl

SirQp as it is drawn from the evaporator
contains suspended solids, commonly known as

sugar sand. They are primarily the calcium and
magnesium salts of malic acid. These salts are
precipitated because they become less soluble

MAPLE SIRUP PRODUCERS MANUAL

as the temperature of the sirup solution in-
creases and as its concentration increases.
Sugar sand occurs in various forms, ranging
from an amorphous black, oily substance to a
fine, white, crystalline material. Dark sugar
sand will usually cause the sirup to appear a
grade or two darker than normal, whereas
white sugar sand will often cause it to appear
lighter.

The amount of this precipitate in the sirup is
not always the same. Sap from the same sugar
grove varies from year to year and even within
the same season.

Studies at the Ohio (Wooster) Agricultural
Experiment Station' indicate that trees at high
elevations tend to produce more sugar sand
than do those at lower elevations. The Ohio
workers were not able to show any relation
between climatological data or soil types and
amounts of sugar sand formed.

Sirup to be sold for table use must be clear
(free of suspended matter) to meet Federal and
some State specifications. Sirup can be clarified
by sedimention, filtration, or centrifugation. On
the farm, sedimentation and filtration are the
methods generally used.

Sediiiieiitatioii

Sedimentation or settling is the simplest
method of clarifying maple sirup, but it has
several disadvantages. It cannot be used to
clarify all sirup. Some sirup contains suspended
particles so fine that they resist settling. Clari-
fication by sedimentation requires a long
time — days and sometimes weeks. After set-
tling at room temperature, the sirup must be
reheated to 180" F. before packaging to insure a
sterile pack. This reheating may darken the
sirup enough to lower its grade.

To clarify by sedimentation, the hot sirup is
first put through a coarse filter, such as several
layers of flannel or cheesecloth, to screen out
large particles of foreign matter. It is then
transferred to the settling tank. The tank
should be of noncorrosive metal, and its height
should be at least twice its diameter. It should
have a dustproof cover and a spigot or other
means of drawing off the sirup about 2 inches
above the bottom of the tank. The sirup should

Unpublished data.

be left in the tank until samples that are
withdrawn show it to be sparkling clear. It is
then drawn from the tank, standardized for
density, heated to 180° F., and packaged. Sirup
that has failed to clarify after several weeks of
standing must be filtered. Because of the un-
certainty of the sedimentation method, it is
rapidly losing favor.

In large operations, the sirup can be kept
sterile if it is added to the settling tank while it
is hot (above 180° F.) and if the entire surface of
the sirup is continuously irradiated by germici-
dal lamps.

Filtration

Filtration of maple sirup is not a simple
procedure. As with sedimentation, the success
and ease of clarifying sirup by filtration depend
on the nature of the suspended particles that
are to be removed. It is best to use two filters —
a prefilter to remove the coarse material and a
thicker filter to remove the fme. In the past,
the most commonly used prefilter was several
layers of cheesecloth, outing flannel, or similar
cloth. Today, a nonwoven rayon material called
miracle cloth or maple prefilter paper is used
with considerable success. After prefiltering,
the sirup is run through a thicker filter. For-
merly these filters were made of wool, but now
they usually are a layer of synthetic felt (Or-
ion).

Synthetic felt filters have many advantages
over wool felt filters. They do not impart a
foreign flavor to the sirup, shrink very little or
not at all, do not pill, resist abrasion, stain only
slightly, and have a long life. Synthetic filters
that have been in use more than 5 years show
little evidence of wear.

The disadvantage of the two-filter system is
that the large particles are removed on the
coarse prefilter. The fme particles are collected
on the finishing filter, and they may form a
compact bed that resists flow of the thick sirup.

The most common filtration assembly in the
past was a large milk can in which was inserted
a cone-shaped, felt bag supported at the top of
the can. However, this is little used today.

Hat Filters

A flat filter consists of a felt sheet for a
filtering surface (fig. 95) instead of a cone. It

AGRICULTURE HANDBOOK 134, U.S. DEFT. OF AGRICULTURE

SUGGESTED FILTER TRAYS
HEAVY GAGE METAL OR WOOD

PN^791

Figure 95. — A simple type of flat filter. A basket of
hardware cloth is supported above the two tanks for
holding the felt and above this is the support for the
prefilter. The prefilter is moved across the tray as new
filtering surface is needed.

was first used in New York and is gaining in
popularity everywhere. The flat filter provides
a larger filtering area than does the cone-
shaped filter. Distribution of the filter cake over
this larger area results in a thiner layer, so the
filters can be used for longer periods before
cleaning is necessary.

The felt sheet is supported in a shallow bas-
ket of hardware cloth with 2-inch walls {147).
The felt is cut at least 4 inches larger than the
bottom of the basket, and the edges are turned
up 2 inches to form a shallow tray (chart 18).
Usually the felt can be used two or three times
longer between cleanings if the sirup is first put
through a prefilter. However, because of the
physical form of the particles of sugar sand,
filtering may be more rapid if the prefilter is
not used. This can be determined only by exper-
iment. The prefilter is mounted above the felt
and is supported on a wire screen basket the
same size as that used for the felt (chart 18).
The prefilter is cut to fit across the basket, but
a length of filter paper is left hanging over the
edge of the basket. As the prefilter becomes
clogged, a new filtering surface is provided by
pulling the prefilter across the basket (fig. 95).

The filters can be built in multiples over a
common tank (fig. 96). As one becomes clogged
with sugar sand, the assembly can be moved to
place a clean filter under the spigot.

FELT FILTER

Chart 18. — Sirup filter. A flat felt filter assembly, con-
structed on a milk-can washer that serves as a tempo-
rary storage tank from which the hot sirup can be
drawn for packaging. Shortening the legs and attach-
ing casters or wheels permits the assembly to be moved
easily into place under the sirup drawoff spigot.

To maintain filtration at a rapid rate the flat
prefilters and felts must be cleaned often, espe-
cially if the sirup contains a large amount of
sugar sand. To clean the filters, the filter cake
is first scraped off with a wooden scraper to
prevent damage to the filtere. The entrapped
sirup is dissolved by dipping the filter into a
pan of hot water. The filters are folded with the
sugar sand on the inside so that it will not be

PX-47y2

Figure 96. — A more elaborate type of installation in
which three felt filter units are installed over a com-
mon tank. The units are mounted on rollers so that
they can be replaced by a fresh unit when necessan,-.
The tank is provided with a drawoff valve.

MAPLE SIRUP PRODUCERS MANUAL

washed into the recovered sirup. The felt is
rinsed repeatedly in hot water. The recovered
sirup is returned to the evaporator.

A homemade washer for flat filters is shown
in figure 97. By means of an eccentric, the felt
is lifted from the hot water and then dunked
repeatedly for 15 to 30 minutes until it is clean.
No detergent can be used since it would impart
an undesirable flavor to the filter. The felts are
then hung on racks to dry or drain. Two or
three extra felts are required for replacements
while the others are being washed. With an
efficient washing machine, the felts can be
reconditioned for use so easily that some pro-
ducers have discontinued using prefilters.

Filtering: Sfiiiiconcenlrtitcd Siriif}

When a finishing pan is used, another filter-
ing procedure has proved very successful. This
procedure takes advantage of these facts: (1)
Most of the sugar sand is precipitated (formed)
and in suspension when the sap is concentrated
to 55° to 60° BrLx, and (2) hot sap at 55° to 60°

PN-4793

Figure 97. — A simple type of machine washes flat filters
by repeatedly dipping the felts into hot water.

Brix has a viscosity of only 1..5° centipoises as
compared to 5.4° for standard-density sirup.
Therefore, when sap has been concentrated to
55° to 60° Brix, it is filtered as it is being
removed from the evaporator and before it is
transferred to the finishing pan. In bringing
the sirup to standard density in the finishing
pan, a small amount of additional sugar sand
(precipitate) may be formed. This is easily re-
moved by using another felt filter assembly.

This final filtration, like all other open filters,
permits loss of water as steam that escapes
from the hot sirup. This may increase the
density of the finished, filtered sirup by as
much as 1° Brix. To avoid this, a number of
producei-s pump the sirup from the finishing
pan through a pipeline to the closed bottling or
canning tank. Since this is a closed system,
there is no change in the density of the sirup as
a result of evaporation. To provide for the final
or polishing filtration, an inline, cartridge-type
filter is mounted in the pipeline from the finish-
ing pan to the holding tank. Two cartridge
filters are used, mounted in parallel with sepa-
rate control valves so that they can be used
alternately. This permits replacing a clogged
filter without inteiTupting the sirup finishing
and filtering operation.

Suiiiinai'v

Sedinientdtiott

(1) Strain the sirup through a paper prefilter or
cheesecloth.

(2) Place the sirup in settling tanks.

(3) Allow it to stand until all suspended matter
has settled out. (Test by periodically draw-
ing a small sample from the tank spigot.)

(4) Sedimentation is complete when the sirup is
ciystal clear as it is drawn off.

(5) If the sirup is still cloudy at the end of
several weeks, it can be clarified only by
filtration.

Filtration {Preferred Method)

(1) Run the hot, standard-density sirup from
the evaporator or finishing tank directly on
the filters.

(2) Use flat (preferably) filters consisting of a
prefilter (paper or flannel) above the felt
filter.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

(3) Change the pre filter and the felt filter as
often as necessai-y to maintain a rapid rate
of filtration.

(4) When using a finishing pan, filter the partly
evaporated sirup before transferring it to
the pan.

(5) If a precipitate forms while the sirup is
heating in the finishing pan, the sirup must
be given a final or polishing filter.

(6) Use a closed system in transferring the
finished sirup to the holding tank and use
an inline, cartridge-type filter for polishing
the sirup.

CHECKJING AND ADJUSTING DENSITY OF SIRUP

The one specification that all gi-ades of table
sirup must meet, irrespective of color or other
considerations, is density. The minimum allow-
able density of maple sirup is 66 percent by
weight of soluble solids (66.0° Brix or 35.6°
Baume)*' {130a). This corresponds to 11.025
pounds per gallon of 231 cubic inches at 68° F.

The density of sirup can be measured in
three ways: (1) By weight; (2) by refractometry;
and (3) by hydrometry.

Vi <Mght Method

Determining the density of sirup by the
weight per unit of volume is not recommended
as a testing procedure for farm use. This test
can be made only under- the most exacting
conditions and with precision instruments. The
gallon measure must have a capacity oi exactly
231 cubic inches, the temperature of the sirup
must be exactly 68° F., and the weight of the
sirup must be determined accurately to within
0.01 pound. If any one of these conditions is in
error, the measurement is valueless. For exam-
ple, an exact gallon of 231 cubic inches of sirup
at 68^ F. with a Brix value of 63.5° weighs 10.90
pounds {107), whereas the same volume of sirup
at the same temperature but with a Brix value
of 67.5° weighs 11.10 pounds. Thus, two sirups
could differ 4 percent in their solids content and
yet differ only 0.2 pound in weight (an amount
not detected by ordinary scales) so they would
both appear to weigh 11 pounds per gallon. Or
an error in weighing of 0.02 pound would cause
an error in the solids content of approximately
V2 percent (0.5° Brix). For these reasons, the
fact that a gallon of minimum density sirup
weighs 11 pounds does not mean that this is a

" Bureau of Standards Baunie scale for sugar solutions,
modulus 14.5.

recommended criterion for measuring the den-
sity of sirup. However, it is of great value when
used properly and should be used to measure
the amount of sirup sold as 1 gallon.

Since sirup is packed hot in cans that are
large enough to allow for the expanded volume
of the hot sirup, and since all sirup is not
packaged at exactly the same hot temperature,
the volume of a gallon of hot, standard-density
sirup varies slightly. However, a gallon of
standard-density sirup weighs 11 pounds
whether it is hot or cold. It is therefore recom-
mended that all packaged sirup be weighed
before it is sold to determine if the required
amount of sirup is in the package — 11 pounds
for 1 gallon; 2 pounds, 12 ounces for 1 quart;
and 1 pound, 6 ounces for 1 pint. These are net
weights and do not include the weight of the
can or package.

Refractometrj' Method

Determining the density of sirup by measur-
ing its refractive index, which changes in a
regular manner with changes in the amount of
dissolved solids, is the simplest of the three
methods. This method is not generally used
because it requires a refractometer, an expen-
sive optical instrument (fig. 98). However, the
precision with which density can be measured
with the refractometer makes it well suited for
use by Federal and State inspection services, by
judges of sirups in competition, and by central
evaporator plants. This instrument is not satis-
factory for measuring the density of hot sirup
(180° F. and above).

H.vdi-oineti-> Method

Hydrometry is the most generally used
method for measuring the density of cold sirup, '

MAPLE SIRUP PRODUCERS MANUAL

PN-4794

Figure 9S. — Checking the density of sirup with a refrac-
tometer. Only one drop of sirup is required for this
measurement.

and it is best suited for use by the sirupmaker.
All that is required to make precise density
measurements is a relatively inexpensive but
accurate hydrometer, a thermometer, and a
hydrometer tube or jar (fig. 99). Hydrometry is
based on the Archimedes principle that the
density of a liquid can be measured by the
displacement of a floating body. The hydrome-
ter, a partly immersed body, displaces a volume
of liquid having a mass equal to the weight of
the hydrometer. A hydrometric measurement
is made by noting the point on the hydrometer
stem that is in contact with the surface of the
liquid. The hydrometer must be at rest and
floating freely in the liquid, as shown in chart
19. The density value is read from a scale sealed
in the stem.

The accuracy of a hydrometer measurement
depends on the spacing of the markings on the
scale in the hydrometer stem, which in turn
depends on the diameter of the stem. Thus, the
thinner the stem, the farther apart the mark-
ings, and the greater the accuracy with which
the density measurements can be made. The
scale of hydrometers for measuring density of
sirup may be marked and calibrated in or on
the stem of the hydrometer (chart 20). These
scales can be marked by one of three systems or
a combination of the systems: (1) Specific grav-
ity; (2) Brix scale; or (3) Baume scale.

HYDROMETER STEM

READING
POINT

Chart 19. — Hydrometer used for measuring density. The
hydrometer can should be filled to the top. It should be
held at eye level for reading.

Both specific gravity and the Baume scale
relate the weight of a unit volume of maple
sirup (the solution being tested) to some other
liquid used as a standard; they give no direct
information regarding the solids content of the
sirup being tested.

Brix Sfdif

The Brix scale relates the density of sirup to
sugar solutions of the same density and known
percentages of sugar. The Brix value does not
express the true percentage of sugar in a solu-
tion containing sugar plus other dissolved sol-
ids; rather, it indicates what the percentage of
sugar would be if the density of the solution
were due only to dissolved sugar. The Brix
scale is particularly well suited for measuring
the density of maple sirup because 98 percent of
the dissolved solids is sugar. For practical pur-
poses, the Brix value equals the percentage of
sugar in the sirup.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

PN-4796

Figure 99. — A hydrometer is a simple, inexpensive instru-
ment for precisely measuring the density (" Brix) of the
sirup. The hydrometer should be read at eye level. The
temperature of the sirup must be measured and a
temperature correction made.

A good approximation of the weight of sugar
in any lot of maple sirup, whether or not it is
standard-density sirup, can be found by multi-
plying the weight of the sirup by its density
(° Brix) and dividing by 100. This information is
important to the producer who sells his sirup
wholesale, since the price is based on its solids
(sugar) content. Thus, 100 pounds of sirup at 65°
Brix contains 65 pounds of sugar, whereas 100
pounds of standard-density sirup (66.0° Brix)
contains 66.0 pounds of sugar. Therefore, 100
pounds of the low-density sirup has a lesser
value than 100 pounds of standard-density sir-
up. Likewise, 100 pounds of sirup with a den-
sity of 66.8° Brix contains 66.8 |X)unds of sugar,
which is more than that contained in 100
pounds of standard-density sirUp, and it has a
greater value. If sirup has an original density
of more than 67° Brix, the excess sugar will
precipitate out, and the hydrometer will not
measure it.

To obtain the weight of sugar in sirup when
density is measured by a hydrometer whose

VT BAUME

(eo'F)

HYDROMETERS

NY BAUME BRIX
(68°E)

BRIX

(ee-E)

r~\

60
61
62

63
64
65
66
-167
J 68

Chart 20. — The three hydrometer scales used in testing
sirup. Left, Vermont Baume scale, marked for testing
sirup at 60° F.; standard-density sirup at this tempera-
ture is indicated by the heavy line at 36°. Center,
hydrometer with double scale, marked for testing sirup
at 68°; standard-density sirup on the Baume scale of
this hydrometer is indicated by the hea\y line at 35.27°.
The double scale requires a spindle so large in diameter
that accurate readings are difficult to make, since the
scale must be compressed, ffi^/if, Brix scale, marked for
testing sirup at 68°; standard-density sirup at this
temperature is indicated by the heavy line at 65.46°.

scale is in specific gi-avity or ° Baume requii-es
more involved calculation because neither scale
has a direct relation to the amount of sugar
present.

Baume Scale

Even though the Baume scale does not ex-
press directly the solids content of maple sirup
and its continued use cannot be recommended,
its long past use by the maple industry justifies
the following explanation and the tabulation on
page 85 for the conversion of Baume values
(points) to ° Brix.

The Baunie scale relates the density of a
liquid to that of a salt solution, but it is more

MAPLE SIRUP PRODUCERS MANUAL

convenient to calculate the Baume value from
specific-gravity tables. Thus, " Baume = sp. g.
(sp. g.)

(M)

, where M = the modulus.

In the past, unfortunately, neither the tem-
perature for which the Baume scale was cali-
brated nor M was standardized. Today, M is
standardized at 145. The temperature for cali-
bration is standardized at 68° F. (except in Ver-
mont). In Vermont, the scale is marked at 36°
(for use at 60° F.), and standard-density sirup
has a Baume reading of 36° when measured at
60° F. In other States and for Federal sjjecifica-
tions, the scale is marked at 35.6° (for use at
68° F.). When this scale is used, standard-den-
sity sirup has a Baume reading of 35.6° at 68°.
When a Baume hydrometer is used, caution
must be exercised in observing the temperature
at which the scale is to be used.

Aleasiirinff Doiisitv

Measuring the density of sirup by hydrome-
try is relatively simple. Many people, however,
incorrectly assume that the observed hydrome-
ter reading is the true density of the sirup. This
error occurs because they neglect to consider
that sirup and sap are water solutions and
therefore behave as water does, expanding and
contracting with changes in temperature.

Most hydrometers and re fracto meters made
for use in this country are calibrated for use at
68° F. When used to measure sirup at this
temperature, the observed hydrometer or re-
fractometer value of the sirup is the true value.
If sirup is heated above 68° F., it will expand to
a greater volume and its apparent (observed)
density will be less than its true density. Like-
wise, if sirup is chilled below 68°, it will contract
to a smaller volume and its apparent (observed)
density will be gi-eater than its true density and
corrections must be made.

To make exact density measurements, sensi-
tive hydrometers that can be read with high
precision must be used. The diameter of the
hydrometer stem, therefore, must be small
enough so that a change in the density of the
sap or sirup equivalent to 0.1° Brix will cause
an observable change in the depth at which the
hydrometer stem floats, as measured at the
intersection of the liquid surface and the hy-

drometer stem. The hydrometer will have a
scale with 0.1° Brix graduations and will usu-
ally cover a range of 10° to 12° Brix. The stem
will be approximately 6V2 inches long, and the
overall length of the hydrometer will be about
13 inches. This type of hydrometer will require
a hydrometer cup at least 13 inches deep.

Since the Brix scale gives the density of sap
or sirup directly in terms of dissolved solids as
percentage of sugar, it is ideally suited for use
by the maple industry. However, as stated ear-
lier, many sirup hydrometers in use today have
Baume scales. Baume values (commonly called
points) can be converted to Brix values, as
follows:

Brix

Baume

Bri,\

Baume

Brix

0.0 0.0

0.1 .1

0.2 .1

0.3 .2

0.4 .2

0.5 ..3

0.6 .3

0.7 .4

0.8 .5

0.9 .5

1.0 .6

1.1 .6

1.2 .7

1.3 .7

1.4 .8

1.5 .8

1.6 .9

1.7 1.0

1.8 1.0

1.9 1.1

2.0 1.1

2.1 1.2

2.2 1.2

2.3 1.3

2.4 1.3

2.5 1.4

2.6 1.5

2.7 1.5

2.8 1.6

2.9 1.6

3.0 1.7

3.1 1.7

3.2 1.8

3.3 1.9

3.4 1.9

3.5 2.0

3.6 2.0

3.7 2.1

3.8 2.1

3.9 2.2

4.0 2.2

4.1 2.3

4.2 2.4

4.3 2.4

4.4 2.5

4.5 2.5

4.6 2.6

4.7 2.6

4.8 2.7

4.9 2.7

5.0 2.8

5.1 2.9

5.2 2.9

5.3 3.0

5.4 3.0

5.5 3.1

5.6 3.1

5.7 3.2

5.8 3.2

5.9 .3.3

6.0 3.4

6.5 3.6

7.0 3.9

7.5 4.2

8.0 4.5

8.5 4.7

9.0 5.0

9.5 5.3

10.0 5.6

10.5 5.9

11.0 6.1

11.5 6.4

12.0 6.7

12.5 7.0

13.0 7.2

Baume

13.5 7.5

14.0 7.8

14.5 8.1

15.0 8.3

15.5 8.6

16.0 8.9

16.5 9.2

17.0 9.5

17.5 9.7

18.0 10.0

18.5 10.3

19.0 10.6

19.5 10.8

20.0 11.1

20.5 11.4

21.0 11.7

21.5 11.9

22.0 12.2

22.5 12.5

23.0 12.7

23.5 13.0

24.0 13.3

24.5 13.6

25.0 13.8

25.5 14.1

26.0 14.4

26.5 14.7

27.0 14.9

27.5 15.2

28.0 15.5

28.5 15.8

29.0 16.0

29.5 16.3

30.0 16.6

30.5 16.8

31.0 17.1

31.5 17.4

86 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

Brix ° Baume ° Brix ° Baume " Brix ° Baume

Measuring Solids (Content

32.0 17.7 58.0 31.5 64.8 34.9 The effect of temperature on density is more

32.5 17.9 58.5 31.7 64.9 35.0 pronounced in siruD than in sap {H6). Since

33.0 18.2 59.0 32.0 . . ■ ' ^u \.u e u

33.5 18.5 59.5 32.2 65.0 35.0 ^^^"P '^ "'^^^ viscous than sap, the followmg

34.0 18.7 65.1 _ __ 35.1 precautions should be observed:

34.5 19.0 gQQ ^2 5 65.2 35.1 No sirup must be allowed on the part of the

35.0 19.3 gjj J 32.5 -~^^-^ ^^-^ hydrometer stem that is exposed above the

35.5 19.6 gQ2 32.6 ^^■'^ ^^-^ surface of the sirup being tested. The hydrome-

60.3 32.6 • • ter must be clean and dry, and it must be

36 n 19 8 fin 4 "^9 1 oo.b 35. o

365 ' ' 20 1 qp 7 65.7 35.4 inserted with clean fingers. Also, it must not be

37.0 V. ... 2QA 606 32 8 ^^-^ ^^-^ submerged below its floating position and per-

37.5 20.6 60.7 32.9 ^^'^ ^^-^ mitted to rise. The sirup on the exposed stem of

38.0 20.9 60.8 32.9 the hydrometer would add weight, the hydrom-

38.5 21.2 60.9 33.0 ^^'^ ^^-^

39.0 21.4

60.9 33.0 • • eter would float too deep in the sirup, and the

48.5 26.5

49.0 26.8

66.1 35.6

go g 21 7 66.2 __ 35.7 observed reading would be too low.

4o!o ~ ~- 22^0 ^^'^ ^^'^ 66.3 35.7 Sirup at room temperature is viscous, and

40.5 22.2 „ ■ „ „■ 66.4 35.8 therefore 30 seconds or more will be required

61 3 V 33 2 ^^'^ ^^'^ fo^ ^^^ hydrometer to settle to its point of rest.

41.0 22.5 61.4 33.2 gg",, org If the observed hydrometer readings are made

41.5 22.8 61.5 33.3 gg'g gg^^ too soon, they will be too high. Also, if the

42.0 23.0 61.6 33.3 gg g gg q diameter of the hydrometer cup is too small, or

43 0 23 6 618 33 4 if the hydrometer is floated too close to the wall

43.5 23.8 619 ... 33^5 ^'"^ ^^'^ of the cup, or if the cup is tilted, the movement

44.0 24.1 ^'^■^ 36.1 of i]]Q hydrometer will be restricted and the

44.5 24.4 g2(, gg g 67.2 36.2 observed reading will be incorrect.

45.0 24.6 g2^ gg g ^^-^ ^^-^ rpQ determine accurately the sugar content of

• • 62.2 33.6 67.5 36.3 maple sirup, use a hydrometer calibrated in 0.1°

4gjj 62.3 33.7 67.6 36.4 Brix (7.46). Place the sirup in a hydrometer cup

46.5 '/.'".'. 2bA 625 33 8 ^''"^ ^^'^ whose depth is equal to, or slightly greater

47.0 25.7 62^6 33.8 67 9 365 than, the overall length of the hydrometer and

47.5 26.0 g2 7 339 ' ' whose diameter is at least IV2 times larger than

'!?■? ??■? 62.8 33.9 ggQ ggg the diameter of the hydrometer bulb. Fill the

62.9 34.0

;.l 36.6 hydrometer cup to the top with sirup, gently set

495 """"'" 27^^ 68.2 36.7 the hydrometer into the sirup, and allow it to

50.0 27.3 ^^"^ ^^-^ 68.3 36.7 settle unaided until it comes to rest. When the

50.5 27.5 f^\ l^-\ 68.4 36.8 hydrometer comes to rest, at least 30 seconds

63.3 34.2 68.6 36 9 after it IS placed m the cup, carefully hit the

51.0 27.8 63.4 34.2 68.7 36.9 cup SO that the liquid surface is at eye level and

51.5 28.1 63.5 34.3 68.8 37.0 read the mark on the hydrometer scale at the

52.0 28.3 63.6 34.3 68.9 37.0 point of intersection of the hydrometer stem

«A fA MS ^11 and the liquid surface (fig. 99). This value is the

53.0 28 9 00.0 o4.4 fiQO '^7 1 <^ n • c \

53.5 29.1 63.9 34.5 egj gfj observed hydrometer reading ( Brix) of the

54.0 29.4 6a2 __"."'" 37^2 ^irup.

54.5 29.6 64.0 34.5 69.3 37.2 Although most hydrometers are calibrated

55.0 29.9 64.1 34.6 69.4 37.3 for use at 68" F., this does not mean that sirup

55.5 30.2 64.2 34.6 69.5 37.3 ^lust be heated or cooled to 68° before its

56.0 ._.... 30.4 61:4 " - 1^1 Z VZ" 111 density can be measured. Actually, the ob-

56.5 30 7 64 5 34 8 69.8 37 5 served density can be measured at any temper-

57.0 30.9 64.6 34.8 69.9 37.5 ature and the true density, or Brix value, calcu-

57.5 31.2 64.7 34.9 70.0 37.6 lated, if the exact temperature of the sirup at

MAPLE SIRUP PRODUCERS MANUAL

the time the reading was made is known. The
temperature of the sirup should be measured
with a pi'ecision Fahrenheit thermometer cali-
brated in intervals of 1.0°, or preferably 0.5°.
Table 14 shows the amount to be added to or
subtracted fi'om the observed Brix reading to
obtain the true density of sirup measured at a
temperature other than 6S' F.

The following examples show how to obtain
the true density of sirup in ° Brix:

Example 1. What is the true density, in
° Brix, of sirup having an observed density of
65.9° Brix at 165° F.?

Since the observed reading is below 69.9°
Brix, the correction to use is in column 2 of
table 14. Locate the temperature 165° F. in
column 1. Opposite this in column 2 is 5.0° Brix,
the correction to add to the observed reading.
Therefore, the true density of this sirup is 65.9°
+ 5.0°, or 70.9° Brix.

Example 2. What is the true density of sirup
having an observed density of 61.0° Brix at
5r F.?

Since the observed reading is below 69.9°
Brix, the correction to use is in column 2 of
table 14. Locate the temperature closest to
57° F. (55° F.) in column 1. Opposite this in
column 2 is 0.5° Brix, the correction to subtract
from the observed reading. Therefore, the true
density of this sirup is 61.0° - 0.5°, or 60.5° Brix.

A<lj listing; Density

Heavy sirup decreases the potential number
of gallons of sirup that can be made from a
quantity of sap. Sirup should, therefore, be
adjusted to the proper density. Further, sirup
with a density of more than 67° Brix (more than
36° Baume at 68° F. or 36.2r Baume at 60° F.)
must be diluted or it will crystallize on storage.
The sirup can be diluted either by adding water
or sap or low-density sirup.

The amount of water needed to adjust 100
pounds of heavy sirup, or any part thereof, to
the standard density of 66.0° Brix is shown in
table 15. If sap or low-density sirup is used, the
amount required can be calculated from the
densities of the two liquids by Pearson's square.
The calculation is explained on page 126.

The calculation for adjusting heavy sirup can
be done accurately only after its true density
(Brix value) has been determined.

If the true density of sirup is known, the
amount of water to add to yield 66'-Brix sirup
can be obtained directly from table 15. After
adding the water, stir the sirup well to insure

Table 14. — Corrections to be applied to ob-
served Brix readings of maple simp to com.-
pensate for effects of tem.perature '

Correction to subtract from (-) or
Temperature of added to ( + ) observed Brix reading
sirup in hydrometer of —

cup, ° F.

60.0°-69.9°

69.9° and higher

(1) (2) (3)

° Brix ° Brix

32 -1.4 -1.5

,35 -, -1.3 -1.4

40 -1.2 -1.2

45 -1.0 -1.0

50 -.8 -.8

55 -.5 -.6

60 -.3 -.4

65 -.1 -.1

68- .0 ,0

70 +.1 +.1

75 +.3 -I-.3

80 +.5 +.5

85 +.8 +.8

90 +1.0 -1-1.0

95 -1-1.2 -1-1.2

100 -1-1.5 -H.5

105 -1-1.7 -1-1.7

110 -1-1.9 -1-1.9

115 -1-2.2 -1-2.2

120 -1-2.4 -1-2.4

125 -1-2.7 -1-2.7

130 -1-3.0 4-2.9

135 -1-3.2 -H3.2

140 -1-3.5 -1-3.4

145 -1-3.8 -1-3.7

1.50 -1-4.1 -1-4.0

155 -1-4.4 -1-4.2

160 -1-4.7 -1-4.5

165 -1-5.0 -1-4.9

170 -1-5.5 -1-5.2

176 -1-5.9 -1-5.7

' If observed reading is in ' Baume, first convert to
Brix (p. 85), then apply the temperature correction.

- Most hydrometers are calibrated at exactly this tem-
perature.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

Table 15. — Water to add to heavy sirup (66.1° to
70.0° Brix) to obtain 66°-Brix sirup

True Brix value of
undiluted sirup '

(1)

Amount of water to add
to heavy sirup ^

Per 100 pounds Per pound

(2) (.3) (4)

Fluid

Pints Ounces ounces

66.1° 0 2 0.02

66.2° 0 5 .05

66.3° 0 7 .07

66.4° 0 10 .10

66.5° 0 12 .12

66.6° 0 15 .15

66.7° 1 1 .17

66.8° 1 3 .19

66.9° 1 6 .22

67.0° 1 8 .24

67.1" . 1 11 .27

67.2° 1 13 .29

67.3° 2 0 .32

67.4° 2 2 .34

67.5° 2 4 .36

67.6° 2 7 .39

67.7° 2 9 .41

67.8° 2 12 .44

67.9° 2 14 .46

68.0° 3 1 .49

68.1° 3 3 .51

68.2° 3 5 .53

68.3° 3 8 .56

68.4° 3 10 .58

68.5° 3 13 .61

68.6° 3 15 .63

68.7° 4 1 .65

68.8° 4 4 .68

68.9° 4 6 .70

69.0° 4 9 .73

69.1° 4 11 .75

69.2° 4 14 .78

69.3° 5 0 .80

69.4° 5 2 .82

69.5° 5 5 .85

69.6° 5 7 .87

69.7° 5 10 .90

69.8° 5 12 .92

69.9° 5 15 .95

70.0° 6 1 .97

' ° Brix of sirup after correction for temperature.

" For practical approximations, pints = pounds avoirdu-
pois, and fluid ounces = ounces avoirdupois.

that the added water has been uniformly mixed
with all the sirup. Then check the Brix value of
the adjusted sirup to be sure that it is the
correct density (66° Brix). Each additional heat-
ing causes an additional darkening of the sirup;
therefore, try to make sirup of the correct
density when the sap is first evaporated.

The following examples show how to use
table 15 in calculating the amount of water to
add to heavy sirup to yield a 66°-Brix sirup.

Example 1. A 100-pound sample of heavy
sirup has a true density of 69.7° Brix. How
much water should be added to adjust this
sirup to 66° Brix?

In table 15 locate 69.7° Brix. Opposite this in
columns 2 and 3 is 5 pints and 10 ounces, the
amount of water to add to the 100 pounds of
heavy sirup to adjust it to 66° Brix.

Example 2. If only 12 pounds of the sirup in
example 1 is being adjusted, how much water
should be added?

Table 15 column 4 shows that 0.9 fluid ounce
of water must be added to adjust 1 pound of
69.7°-Brix sirup to 66° Brix. For 12 pounds,
12x0.9 or 10.8 fluid ounces of water is required
to adjust 12 pounds of 69.7°-Brix sirup to 66°
Brix.

Example 3. How much water should be added
to 26 pounds of 68.2f'-Brix sirup to change its
density to 66° Brix?

In table 15 locate 68.2° Brix. Opposite this in
column 4 find the value of 0.53 fluid ounce, the
amount of water to add to 1 pound of 68.2f-Brix
sirup. Then, 26x0.53, or 13.8 fluid ounces of
water is required to adjust 26 pounds of 68.2°-
Brix sirup to 66° Brix.

Summary

(1) Do not check the density of sirup by weight,
unless precision instruments are available.

(2) The minimum allowable density is 66.0°
Brix (at 6? F.) or 35.6° Baume (at 68° F.).
Sirup that has a density of 66.5° to 67° Brix
(at 68^ F.) has a higher viscosity and tastes
better.

(3) To test the density of sirup with a hydrome-
ter, fill the can or jar to the top with sirup.

(4) Use only a clean, dry hydrometer.

(5) Lower the hydrometer into the sirup care-
fully until it comes to rest.

MAPLE SIRUP PRODUCERS MANUAL

(6) Hold the can so the top is at eye level and
read the value on the hydrometer scale at
the surface of the sirup. The value is the
observed or apparent density of the sirup.

(7) To determine the true density of the sirup

from the observed hydrometer reading,
measure the precise temperature of the sir-
up and add to, or subtract from, the ob-
served hydrometer reading, depending on
how much warmer or cooler than 68" F. the
sirup is, using table 14.

GRADING SIRUP BY COLOR

Color Standards

Sirup should be graded before it is packaged.
Vermont producers are required to state on the
label the grade of sirup they are offering for
sale to consumers (131). Color is the principal
grade-determining factor of table sirup that
meets other requirements, such as density, fla-
vor, and cloudiness.

The U.S. Department of Agriculture color
standards are designated "Light Amber," "Me-
dium Amber," and "Dark Amber." These corre-
spond to Bryan Color Nos. 6, 8, and 10.

The original U.S. color standards were solu-
tions of caramel in glycerin made according to
Balch's U) revised spectrophotometric specifica-
tions for Bryan color Nos. 6, 8, and 10. Master
sets of these three solutions were supplied each
year for Federal and State inspection of maple
sirup. Unfortunately, these caramel solutions
tend to fade. They should not be kept for use as
standards for more than 1 year.

U.S. Color Comparator

The U.S. Department of Agriculture has de-
veloped a simple type of color comparator with
permanent standards of colored glass (9, 10).
These standards became the official U.S. De-
partment of Agriculture color standards for
maple sirup in 1950 and were adopted by the
Association of Official Agricultural Chemists
(153). The colors of the different gi-ades of sirup
are given in table 16. A thick layer of the sirup
to be tested is placed in the comparator (fig.
100). This aids in precise grading because the
standards are widely spaced on a color scale
when viewed in this thickness. The square con-
tainer provides a field of view of uniform thick-
ness and color, a feature that was not possible
with the cylindrical bottles formerly used.

The three clear blanks supplied with the
color-grading kit are placed in the compart-

PN-n96

Figure 100. — Color-grading kit. The kit consists of the
official USDA permanent glass color standard mounted
in a comparator. The three clear blanks are in position
in the compai-ator. For viewing, the sirup sample in the
bottle to the right of the comparator is mounted in one
of the two openings in the comparator.

Table 16. — Grade designations of maple sirup,
as determined by color

Grade designation

Color

Color index
range '

U.S. Grade AA

(New York

Fancy or

Vermont Fancy).
U.S. Grade A (New

York No. 1 or

Vermont A).

U.S. Grade B (New
York No. 2 or
Vermont B).

Unclassified (New
York No. 3 or
Vermont C).

As light as or lighter
than Light Amber.

Darker than Light
Amber but as light
as or lighter than
Medium Amber.

Darker than Medium
Amber but as light
as or lighter than
Dark Amber.

Darker than Dark
Amber.

■ For description of color index, see p. 45.

ments in back of the three standard glasses:
Light; Medium; and Dark Amber.

The sirup to be graded is poured into one of
the clean square glass bottles and placed in one
of the two open compartments. The comparator
is held at a convenient distance from the eye

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

and is viewed toward the sky but away from
the sun (fig. 101). The color grade (classification)
of the sirup is determined by comparing the
samples with the standards. If the sample of

PN-n97

Figure 101.— The sirup and color standards are viewed
toward the sky (away from the sun), preferably toward
the north sky.

sirup is cloudy, its true color classification may
be difficult to determine because its brightness
will be lowered.

Information concerning the color-gi-ading kit,
including the comparator block with glass
standards, may be obtained by writing to the
Pi-ocessed Products Standardization and In-
spection Branch, Agricultural Marketing Serv-
ice, USDA, Washington, D.C. 20250.

Suininai7

(1) Color is the grade-determining factor for
table sirups that meet all other require-
ments such as density, flavor, and cloudi-
ness.

(2) Grade the color of the sirup by visually
comparing it with color standards.

(3) Use as standards either the U.S. Depart-
ment of Agi-iculture permanent glass stand-
ards (preferred) or suitable caramel-glycerin
solutions.

(4) Do not use caramel-glycerin standards that
are more than 1 year old.

(5) Designate the color of the sirup as either
Light Amber, Medium Amber, Dark Amber,
or Darker Than Dark Amber.

PACKAGING

The graded and clarified sirup with a density
between 66° and 67° Brix at a temperature of
68f F. is ready for packaging (fig. 102). If the
temperature of the sirup when tested after
filtering is still above 180°, the sirup can be
packaged immediately. If the sirup has cooled
below 180°, it must be reheated. However, the
sirup may become darkened if the temperature
goes above 200° when it is reheated.

As stated previously, maple sirup is a water
solution. Like water, sirup expands and con-
tracts with changes in temperature. For this
reason it is difficult to package hot sirup accu-
rately by volume. Accurate packaging 'can be
done only if the sirup is adjusted to that tem-
perature for which the volume of the can will
hold an exact gallon. Since standard-density
sirup weighs the same regardless of its temper-
ature, it is best to package maple sirup by
weight! The sirup can be weighed on ordinaiy
household scales. However, it is advisable to

test the scales before they are used. This can be
done by taking the scale to a gri-ocery store and
comparing it with the grocer's certified scales.
To do this, weigh an object that weighs exactly
1, 2, or 10 pounds (such as a bag of sugar or a
can of water) on the gi'ocer's scale. Then weigh
it on the scale being tested. If possible, adjust
the household scale to make it read correctly. If
it cannot be adjusted, make a calibration chart
by recording in one column the household scale
reading and in the other the corresponding true
weight.

When packaging sirup by weight, allowance
must be made for the weight of the container.

After the container has been filled with the
correct weight of sirup, it is sealed and laid on
its side so that the hot sirup contacts the
closure and pasteurizes it. After the containers
have been on their sides 10 to 15 minutes, they
are readv for cooling.

MAPLE SIRUP PRODUCERS MANUAL

PN-479H

Figure 102. — Sirup being packaged in lithographed cans.

Stack BiiiTi

If packaged sirup is stacked while it is still
hot, the same browning reaction that occurred
in the evaporator will continue and darken the
sirup by as much as one or two grades. This
seldom occurs with fancy grades of sirup. De-
velopment of color in hot packaged sirup is
called stack bum. To prevent stack bum, the
containers should be temporarily stacked with
an air space to allow air to circulate, and a fan
should be used to speed up cooling. After the
cans have cooled to room temperature, they can
be close packed.

Control of \Iiero-Org;anisins

Standard-density sirup will not support ac-
tive growth of micro-organisms with the excep-
tion of a few types of yeast and one or two types
of bacteria. Because of the possible contamina-
tion of sirup with these organisms, sirup that is
offered for sale to the consumer should be
packaged hot. The sirup must be heated to at
least 180° F. and then packaged immediately
(27).

Everyone has seen mold growing on sirup.
However, mold will not grow in standard-den-
sity sirup. These apparently contradictory
statements are explained as follows: Cold-
packed maple sirup may contain mold spores.
The mold spores, like the spores of most yeast
and bacteria, will remain in a resting state and
will not germinate as long as all the sirup is of
standard density.

Sirup stored under ordinary conditions usu-
ally undergoes some temperature change.
When the storage temperature increases, some
of the water of the sirup is distilled up into the
head space of the container. When the storage
temperature decreases, this vapor condenses
into small drops of water that run down onto
the surface of the sirup and produce a layer of
low-density sirup in which mold and other types
of spores can vegetate and grow.

Even though the sirup contains spores, their
growth can be prevented by momentarily in-
verting the packaged sirup once or twice
weekly (7J^). This destroys the layer of dilute
sirup and thus inhibits germination of the mold
spores.

Although sirup is packaged under clean, sani-
tary conditions, this does not guarantee that
the sirup will not become inoculated with micro-
organisms if it is packaged cold. Once mold or
yeast has grown in the area where cold packag-
ing is done, it is almost impossible to package
sirup by the cold method without its becoming
infected.

Chemical inhibitors have long been used for
preserving foods. Studies (30) have shown that
one of these, the sodium salt of propyl parahy-
droxybenzoate (PHBA), is effective in control-
ling growth of yeast and mold in maple sirup. A
concentration of only 0.02 percent is required.
Sodium propyl PHBA is available commercially
under different trade names.

CAUTION

Before iisin

g this

or any other chemical

preservative.

detei

■mine whether it has

been approved by

your Slate for use in

intraslate sal

's and

by the Federal Foo<l

and Drug Atl

minis!

ration for use in inter-

stale sales.

AGRICULTURE HANDBOOK 134, U.S. DEFF. OF AGRICULTURE

Bulk-stored sirup can be kept free from sur-
face infection with spoilage micro-organisYns by
irradiating the surface of the sirup with germi-
cidal lamps that emit low ultraviolet radiation,
particularly in the region of 260 millimicrons
{133). The lamps must be mounted to illuminate
the entire surface of the sirup (chart 21).

CAUTION

Never expose the eyes to radiation fi-om
gennieidal lamps sinee pennanent dam-
age ean result. Always turn tli«' lights off
before working in the area illuminated hy
these lamps.

Size and Type of Paekage

The size and type of package are important
when sirup is made for retail sale. Housewives
dislike to repackage sirup from a gallon con-
tainer to smaller ones for use as occasion de-
mands. This has been demonstrated by the
growing tendency on the part of the public to
buy maple sirup in quart or even smaller pack-
ages.

The net weights for standard-density sirup
are: 1 gallon weighs 11 pounds; 1 quart weighs
2 pounds and 12 ounces; 1 pint weighs 1 pound
and 6 ounces. Since sirup must be packed hot
(180° F. or above), the capacity of the container
must be at least large enough to allow for the
volume of the heat-expanded sirup. The volume
of 11 pounds of standard-density sirup is 231
cubic inches at 68° F. (20° C); its volume at
212° F. is 239.9 cubic inches. Thus, a gallon
container should have a minimum capacity of
241+1 cubic inches; quart containers, 60.2t0.5
cubic inches; and pints, 30.1±0.5 cubic inches.

Consumers expect sirup to be as attractively
packaged as other foods (fig. 103). When sold at
roadside stands, sirup packaged in tin con-
tainers is attractive to tourists regardless of
the size of the container, because they do not
have to take special care in storing tin con-
tainers in the car as they must with glass
containers. All metal containers should be care-
fully inspected before they are filled to be sure
they are free of all foreign matter and contain
no insects or rodents or their debris.

ULTRAVIOLET
TUBE

REFLECTOR

COVER

Chart 21. — Ultraviolet (germicidal) lamp must be posi-
tioned to illuminate the entire surface of the sirup.
More than one lamp may be required.

Both glass and tin packages should be attrac-
tively labeled. The printed label must be put on
squarely, and the outside must be clean. Many
producers are finding that cans with the labels
lithographed on the tin make an ideal package.

Suiiiiiiai^

(1) Package sirup hot (180° F. or above).

(2) Do not reheat sirup above 200°.

(3) Fill sirup package by weight rather than
by volume.

(4) In packaging by weight, allow for the
weight (tare) of the container.

(5) Use scales that have been tested and cali-
brated against certified weights.

(6) Avoid stack bum by cooling the packaged
sirup before close stacking it.

(7) Control mold gi-owth in cold-packed sirup
or in sterile sirup that has been opened
and exposed to infection by inverting the
container once a week.

(8) Yeast spoilage can be prevented only by
hot packing.

(9) The chemical inhibitor sodium propyl
PHBA in 0.02- percent concentration is ef-
fective in controlling mold and yeast
growth in sirup. CAfT/O.V— Obtain State
and Federal approval before use.

MAPLE SIRUP PRODUCERS MANUAL

Figure 103. — Maple sirup can be packaged in a variety of containers.

(12) Package sirup in small containers such as
quarts, pints, and one-half pints, as well as
gallons and one-half gallons.

(10) Use germicidal lamps to irradiate surface
of sirup in bulk storage to prevent spoilage.

(11) Package sirup neatly in attractive con-
tainers.

STANDARDS FOR MAPLE SIRL P FOR RETAIL SALE

Maple sirup producers often find it profitable
to sell their sirup directly to consumers. In
doing so, farmers not only are producers; they
also are food processors. As food processors,
they are expected to offer for sale a product
that meets Federal and State requirements,
and they must package their sirup so that it
will compare favorably in appearance and qual-
ity with other luxury food items.

Vermont has taken the lead in the United
States in enacting regulations governing the
sale and labeling of maple products {131). New
York (83) and Wisconsin {138), among other
States, are establishing similar regulations. To
obtain information regarding your State regu-
lations governing the sale of maple products,
write to the Division of Mai'kets, Department of

Agriculture, at your State capital. These regu-
lations protect the buyer and assure him that
the product he has purchased meets certain
minimum standards. They also protect the pro-
ducer against unfair competition.

The United States standards for table maple
sirup (129) are as follows:

UNITED STATES STANDARDS FOR
GRADES OF TABLE MAPLE SIRUP

Effective May 24, 1967
Product Description

(a) "Maple sirup" means sirup made by the evaporation
of maple sap or by the solution of maple concrete (maple
sugar) and contains not more than 35 percent of water,
and weighs not less than 11 pounds to the gallon (231
cubic inches).

AGRICULTURE HANDBOOK 1.34, U.S. DEPT. OF AGRICULTURE

(b) The standards in this subpart are issued for the
purpose of classifying maple sirup packed in containers
for table use. It is not intended that they shall apply to
sirup which is packed in drums or other large containers
for later reprocessing. Another set of standards entitled
"U.S. Standards for Maple Sirup for Reprocessing" has
been issued for this purpose (§ § 52.5921-62.5926).

Grades

U.S. Grade AA (Fancy) .

U.S. Grade AA (Fancy) Table Maple Sirup shall consist
of maple sirup which meets the following requirements:

(a) The color shall not be darker than light amber as
represented by the color standards of the U.S. Depart-
ment of Agriculture.

(b) The sirup shall not be cloudier than light amber
cloudy standard as represented by the standards of the
U.S. Department of Agriculture for cloudiness.

(c) The weight shall be not less than 11 pounds per
gallon of 231 cubic inches at 68 degrees F. corresponding
to 65.4' degrees Brix or 35.27 degrees Baume (Bureau of
Standards Baume scale for sugar solutions, modulus 145).

(d) The sirup shall possess a characteristic maple flavor,
shall be clean, free from fermentation, and free from
damage caused by scorching, buddiness, any objectiona-
ble flavor or odor or other means.

U.S. Grade A

(a) U.S. Grade A Table Maple Sirup shall consist of
maple sirup which meets the requirements for U.S. Grade
AA (Fancy) Table Maple Sirup except for color and cloudi-
ness.

(b) The color shall not be darker than medium amber as
represented by the color standards of the U.S. Depart-
ment of Agriculture.

(c) The sirup shall not be cloudier than medium amber
cloudy standard as represented by the standards of the
U.S. Department of Agriculture for cloudiness.

U.S. Grade B

(a) U.S. Grade B Table Maple Sirup shall consist of
maple sirup which meets the requirements for U.S. Grade
AA (Fancy) Table Maple Sirup except for color and cloudi-
ness.

(b) The color shall not be darker than dark amber as
repre.sented by the color standards of the U.S. Depart-
ment of Agriculture.

(c) The sirup shall not be cloudier than dark amber
cloudy standard as represented by the standards of the
U.S. Department of Agriculture for cloudiness.

' The density requirement was changed in 1974 to 66.0°
Brix {130a).

Unclassified

Unclassified Table Maple Sirup shall consist of maple
sirup which has not been classified in accordance with the
foregoing grades. The term "Unclassified" is not a grrade
within the meaning of the standards in this subpart but
is provided as a designation to show that no definite
grade has been applied to the lot.

Tolerance, Packing

Tolerances for preceding grades

In order to allow for variations incident to proper
grading and handling, not more than 5 percent, by count,
of the containers in any lot may have sirup below the
requirements for the grade: Provided, That no part of this
tolerance shall be allowed for defects causing "serious
damage": And provided further. That no tolerance is
permitted for sirup that is darker in color than that
which is required for the next lower grade.

Packing

(a) Containers shall be clean and new in appearance.
Tin containers shall not be rusty.

(b) In order to allow for variations incident to proper
packing, not more than 5 percent, by count, of the con-
tainers in any lot may fail to meet these requirements.

Explanation of Terms

(a) "Cloudiness" means presence in suspension of fine
particles of mineral matter, such as malate of lime,
"niter," "sugar sand," or other substances that detract
from the clearness of the sirup.

(b) "Clean" means that the sirup shall be practically
free from foreign material such as pieces of bark, soot,
dust, and dirt.

(d) "Serious damage" means any defect that seriously
affects the edibility or market value of the sirup. Badly
scorched sirup, buddy sirup, fermented sirup or sirup that
has any distasteful foreign flavor or disagreeable odor
shall be considered as seriously damaged.

Summary

(1) Sirup sold directly to the consumer must
meet State and Federal specifications.

(2) The package and label must meet State and
Federal specifications.

(3) Know your State law and Federal specifica-
tions governing the retail sale of maple
products.

\1APLE PRODUCTS

Many producers have found that the gross
returns of their maple crop can be increased
fi'om 20 to 160 percent by converting their sirup

to sugar or to confections such as maple cream,
soft sugar candies, and maple spreads. The 8
pounds of sugar in a gallon of sirup is worth $1

MAPLE SIRUP PRODUCERS MANUAL

a pound, based on sirup selling at $8 per gallon.
This same weight of sugar, if converted to
sugar products, can be sold at prices ranging
from $1.50 to $2.50 per pound or a gross of $12
to $20 per gallon of sirup. This increase in gross
returns is usually more than commensurate
with the additional labor involved in converting
sirup to sugar products.

Equipment

Making the different maple sugar products is
not difficult, nor does it require expensive or
unusual equipment. It does require the same
type of care and sanitation that is expected of
any candy company. Maple confections should
be made in a special room, either in the home
(fig. 104) or in a part of the evaporator house
(fig. 105). In some States the law specifies that

confections for sale cannot be made in the home
kitchen.

High-pressure steam is the ideal source of
heat for evaporating sirup in making confec-
tions. High-pressure steam heat can be easily
and instantaneously controlled; and, unlike
other types of heat, there is no danger of
scorching the sugars. When steam is not availa-
ble, gas is preferred. Gas heat is also easily
controlled (fig. 106). Bottled gas is available
almost everywhere.

The size of the equipment (kettles, mixers,
and pans) depends on the amount of sirup to be
pi-ocessed. A thermometer with a range of 200°
to .300° F. in 1° units is a necessity; it can be
either a dial thermometer or a candy thermom-
eter. Other equipment includes measuring cups,
wooden ladles, wooden paddles, and a house-

Figure lOi.—A porch converted to a candy kitchen and salesroom.

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

F'N-IK(I1

Figure 105. — A separate room built in the evaporator
house makes an ideal candv kitchen.

PN-4802

Figure 106. — Gas, whether supplied from tanks or mains,
is a good source of heat for cooking maple products. The
heat is.easily controlled and can be stopped the instant
cooking is completed. Here, sirup is being cooked for
maple cream.

hold scale. Provision should be made for cooling
the sugar products. This is especially desirable
when making maple cream, fondant, or crystal-
coating sirup. The cooler for cream can be a
trough with circulating cold water into which
the pans of cooked sirup are placed. A pan of
chipped ice or ice water may also be used. For
crystal-coating sirup, an insulated box, such as
a used refrigerator from which the cooling unit
has been removed, may be used.

Mapir .Siifiar
('ln'ini.ttry of Mii/ilf Siifiar

Maple sirup is essentially a solution of su-
crose in water. The amount of sugar that can
be in true solution in a given volume of water
varies with the temperature of the solution ill,
12, 51, 82). Hot solutions can contain more sugar
and cool solutions less sugar.

Maple sirup solutions containing 67 percent
of sugar (67° Brix) are saturated at room tem-
perature (68° F.). That is, no more sugar can be
dissolved in the solution at that temperature.
Sirup that has been heated to raise the boiling
point of the sirup to 7.5° F. or more above the
boiling point of water will be supersaturated
when it cools to room temjierature; it will con-
tain more than 67 percent of sugar. This super-
saturated sirup, with its excessive sugar con-
tent, is in an unnatural or abnormal condition,
and it tends to return to normal by ridding
itself of the excess sugar so that the sirup will
again contain only 67 percent of sugar. The
excess sugar is forced out of solution (precipi-
tated), and sugar crystals are formed. The
slower this occurs, the larger the sugar crys-
tals.

To make any of the maple sugar products, it
is necessary first to make supersaturated sirup.
The degree of supersaturation is increased as
the boiling temperature of the sirup is in-
creased and more water is evaporated from the
sirup. When the amount of supersaturation is
small and cooling is slow and is accompanied by
little or no agitation, the state of supersatura-
tion may persist for a longtime; and little sugar
will be precipitated. When the amount of super-
saturation is appreciable, as when sirup is
boiled 'to 18° F. or more above the boiling }X)int
of water (11° or more above that of standard-

MAPLE SIRUP PRODUCERS MANUAL

density sirup), the sirup will appear to solidify
on cooling. This solid cake is mostly sugar, but
some liquid sirup (mother liquor) is mixed with
the sugar.

Fornintion of Crystal Sugar

The crystalline or grainy nature of the pre-
cipitated sugar is determined by a number of
factors, all of which are influential in making
the desired type of confection (8i). These factors
include the degree of supersaturation, seeding,
the rate of cooling, and the amount and time of
stirring.

Large crystals called rock candy, which rep-
resent one extreme, are formed when slightly
supersaturated sirup (67° to 70° Brix) is cooled
slowly and stored for a long time without agita-
tion. A glasslike noncrystalline sirup represents
the other extreme. This is formed when highly
supersaturated sirup (the boiling point is ele-
vated ISf F. or more above the boiling point of
water) is cooled rapidly to well below room
temperature without stirring. The sirup be-
comes so viscous that it solidifies before crys-
tals can form and grow. If the hot supersatur-
ated sugar solution is stirred while it is cooling,
the tendency to form crystals increases. The
mechanical shock produced by the stirring
causes microscopic crystal nuclei to fonn. Con-
tinued stirring mixes the crystals throughout
the thickened sirup, and they grow in numbers
and in size. When the number of crystals is
relatively small, stirring causes the largest
crystals to grow larger at the expense of the
smaller ones. Thus, a grainy sugar tends to
become more grainy the longer it is stirred.

To produce maple sugar with crystals that
are imperceptible to the tongue (impalpable),
the crystals must be kept very small, even
microscopic in size. This is accomplished by first
suddenly cooling a hot, highly supersaturated
sirup so that a viscid, noncrystalline, glasslike
mass is obtained. Then while it is still in the
supei'saturated state, fine crystals, called seed,
are added to serve as nuclei, and stirring is
begun. Since the mass is so highly supersatur-
ated, billions of tiny crystals are formed at the
same time, and the result is a very fine grained
pi'oduct.

Invert Siigiir

Although sucrose is the only sugar in sap as
it comes from the tree, some of the sucrose is
changed into invert sugar as a result of micro-
bial fermentation during handling and process-
ing. Both sucrose and invert sugar are made up
of two simple sugars, dextrose and levulose. In
sucrose, these sugars are united chemically as a
single molecule; in invert sugar, they occur as
separate molecules.

A small amount of invert sugar is desirable in
maple sirup that is to be made into maple sugar
and maple confections. Invert sugar tends to
reduce supersaturation, that is, more sugar can
be held in solution before crystallization occurs.
This helps keep the product moist (62). Also, it
encourages the formation of exceedingly small
sugar crystals. But too little invert sugar in the
sirup will cause the product to be grainy; too
much may prevent formation of crystals
(creaming) as required for making maple
cream. In general, all grades of maple sirup
contain some invert sugar, the amount varying
with the different grades. Fancy has the least;
and U.S. Grade B or unclassified, the most.
Thus, the grade of sirup should be a determin-
ing factor in selecting sirup for making a spe-
cific confection.

A simple chemical test to determine the
amount of invert sugar in maple sirup is de-
scribed on page 113. If the amount of invert
sugar in the sirup is so small that a fine
crystalline product cannot be made, a "doctor"
solution is required (60).

'^Doctor" Solutions

The simplest "doctor" solution and the one
most commonly used is U.S. grade B pure
maple sirup, which is naturally rich in invert
sugar (more than 6 percent, as determined by
the chemical test described on p. 113). As a rule,
dark sirup made from sap produced during a
warm spell contains a high percentage of invert
sugar. The addition of 1 pint of this doctor sirup
to 6 gallons of maple sirup low in invert sugar
(less than 1 percent) usually will correct invert
deficiency.

When sirup with a high content of invert
sugar is not available, the doctor solution can
be prepared as follows: To 1 gallon of standard-

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

density maple sirup add 2V2 liquid ounces of
invertase (an enzyme that causes the inversion
of sucrose to invert sugar). Stir the mixture
thoroughly and allow it to stand at room tem-
perature (65° F. or above) for several days. Dur-
ing this time sufficient invert sugar will form so
that 1 pint of this solution can be used to doctor
6 gallons of maple sirup low jn invert sugar.
Invertase may be purchased from any of the
confection manufacturers.

Another convenient type of doctor is an acid
salt such as cream of tartar (potassium acid
tartrate). Addition of V2 teaspoon of cream of
tartar to 1 gallon of low- in vert sirup just before
it is boiled for candymaking will cause sufficient
acid hydrolysis or inversion of the sucrose to
form the desired amount of invert sugar.

Maple Cream or Butter

The amount of the maple sirup crop that is
being converted into maple cream or butter has
been increasing rapidly. Some producers have
built up so large a demand for this confection
that they convert their entire sirup crop to
cream. Some producers make from 2 to 3 tons of
this confection annually.

Maple cream (8i, 85), a fondant-type confec-
tion, is a spread of butterlike consistency. It is
made up of millions of microscopic sugar crys-
tals interspaced with a thin coating of satu-
rated sirup (mother liquor). The crystals are
impalpable to the tongue and give the cream a
smooth, nongritty texture. The first step in
making maple cream is to make a supersatur-
ated sugar solution. This solution is cooled to
room temperature so quickly that crystals have
no chance to form. The cooled, glasslike mass is
then stirred, which produces the mechanical
shock necessary to start crystallization.

Sirup for Creaming

For best results, U.S. Grade AA (Fancy) or
U.S. Grade A (No. 1) maple sirup should be used.
However, any sirup may be used provided it
contains less than 4 percent of invert sugar.

Invert Sugar Content

The amount of invert sugar in the sirup
selected for creaming should be determined by
the simple chemical test described on page 113.

Sirup that contains from 0.5 to 2 percent of
invert sugar should make a fine-textured cream
that feels smooth to the tongue. Sirup with
from 2 to 4 percent of invert sugar can be made
into cream by heating it to 25° F. above the
boiling point of water (instead of the usual 22°
to 24°). Sirup with more than 4 percent of invert
sugar is not suitable for creaming. It will not
crystallize, or it will crystallize only if heated to
a much higher-than-normal temperature. How-
ever, the cream will be too fluid and probably
will separate a few days after it is made.

The belief throughout the maple- producing
area that maple cream should be made only
from first-run sirup and that all first-run sirup
will yield a good cream is false. It is the amount
of invert sugar in the sirup that determines its
suitability for creaming, not the run of sap from
which the sirup is made. The amount of invert
sugar formed is directly proportional to the
amount of microbial fermentation of the sap.
This, in turn, is related to the temperature.
Unseasonably warm weather is not uncommon
during the first period of sap flow. Warm
weather favors fermentation of the sap, and
sufficient invert sugar is produced to make the
early-run sirup unsuitable for making into
cream.

Since most Fancy and Grade A sirup nor-
mally contains an adequate amount of invert
sugar, the use of a doctor solution is not recom-
mended. The addition or formation of too much
invert sugar will ruin the sirup. Sirup for
creaming should be selected on the basis of the
quick test for invert sugar.

Cooking an(t Cooling

The sirup is heated to a temperature 22° to
24° F. above the boiling point of water (37). (The
temperature of boiling water must be estab-
lished at the time the sirup is boiled for cream-
ing.) The boiling temperature indirectly adjusts
the amount of sirup (mother liquor) left sur-
rounding the crystals; this, in turn, governs the
stiffness of the final product. As soon as the
boiling sirup reaches the desired temperature,
it should be removed from the heat and cooled
quickly. If the cooked sirup is left on the hot
stove (even with the heat turned off), enough
additional water will be evaporated to produce
a more concentrated sirup than desired.

MAPLE SIRUP PRODUCERS MANUAL

Rapid cooling is necessary to prevent crystal-
lization. To provide a large cooling surface, the
sirup is poured into large, flat-bottom pans. The
layer of sirup should be not more than 1 to 3
inches deep. The pans are set in a trough
through which cold water (35° to 45° F.) is flow-
ing (fig. 107).

The sirup is cooled to at least 70° F., and
preferably to 50° or below. It is sufficiently cool
when the surface is firm to the touch. If crys-
tals appear during the cooling process, cooling
is too slow, the pan was agitated, or the invert
sugar content of the sirup is too low for the
cooling conditions. This situation can be cor-
rected either by more rapid cooling (using thin-
ner layers of sirup or more rapid flow of cold
water) or by increasing the invert sugar con-
tent of the sirup by use of a doctor.

Creaming

The chilled, thickened sirup should be
creamed either by hand or mechanically in a
room having a temperature of 70° F. or above.
Many producers have developed their own me-
chanical cream beaters (fig. 108); also, there are
a number of inexpensive ones on the market.

Figure 108. — Homemade cream beaters in which the stir-
rers are held stationary and the pan is rotated at
approximately 50 r.p.m.

The homemade maple cream beater (fig. 109)
consists of a pan approximately 13 inches in
diameter that holds about 1.5 gallons of cooked
sirup. In this beater, the scrapers are held
stationary and the pan revolves at 40 to 50
revolutions per minute. In other beaters, this
procedure is reversed. Both types worked
equally well.

A hardwood paddle having a sharp edge 2 or
3 inches wide is used for hand beating (stirring).
The cooked sirup is poured onto a large flat pan
such as a cookie tin. The pan is held firmly, and
the thick sirup is scraped first to one side and
then to the other. Mixing should be continuous.

PN-1XU3

Figure 107. — Sirup that has been concentrated for cream-
ing is poured immediately into large, flat-bottom pans,
which are set in flowing cold water to cool to well below
room temperature. The sirup is sufficiently cool when
the surface is firm to the touch.

PN^805

Figure 109. — At the beginning of the creaming operation,
the butterlike mass has a shiny surface. When the
surface becomes dull, creaming is complete.

100

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

If stirring is stopped, some of the crystals will
jji-ow and make the product grritty.

While being- stirred, the chilled sirup first
tends to become fluid and then begins to stiffen
and show a distinct tendency to set. At this
time the batch loses its shiny surface (fig. 109).
If creaming is stopped too soon, that is, while
the batch is too fluid, large crystals will form.

To hasten the creaming process, a small
amount of "seed" (previoi^sly made cream) can
be added to the glasslike chilled sirup just
before beating. The addition of 1 teaspoonful of
seed for each gallon of cooked sirup will provide
crystals to serve as nuclei for the more rapid
formation of crystals. The entire creaming proc-
ess may require ft-om 1 to 2 hours, depending on
the size of the batch, but the use of seed will
often shorten the time by half.

Holding Cream for Delayed Packaging

Often it is not convenient to package the
cream at the time it is made. In this case, it can
be stored or aged for periods from 1 day to
several weeks in tightly covered glass or
earthen vessels, preferably under refrigeration.
Many candymakers believe that aging a fon-
dant is desirable because it permits the crystals
to equalize in the saturated .sirup. Some pro-
ducers age the cream 1 day by holding it in an
open pan covered with a damp cloth; they
package the second day without rewetting.
Other producers remelt the aged cream for ease
of pouring and packaging by carefully heating
it in a double boiler (99). The temperature of the
cream during this reheating must not go above
150° F. (The temperature can be controlled by
not permitting the water in the double boiler to
go above 150°.) If the temperature of the cream
exceeds 150°, too much sugar will be dissolved,
and large crystals may form when the remelted
cream is cooled and stored.

Packaging and Storing

Maple cream can be packaged in tin, glass,
plastic, or wax-paper cups. Container with wide
mouths are best for easy filling. Care must be
taken to keep air bubbles from forming, espe-
cially when the cream is packaged in glass
because the air bubbles are unpleasing in ai>
pearance and create the impression the pack-
age is short in weight. Furthermore, air pockets

provide a place where the separated mother
liquor can collect, and this also produces an
unpleasant appearance.

Fi-eshly made cream should be packaged im-
mediately, before it "sets up" (fig. 110), or
within a day if it has been covered and set aside
to age. Remelted cream should be packaged
while it is still warm and fluid. Since maple
cream is a mixture of sugar crystals and satu-
rated maple sirup, storing packaged cream at
70° F. or above will cause more sugar to be
dissolved. The sirup tends to separate as an
unattractive, dark, liquid layer on the surface
of the cream. This sirup layer also forms if the
cream is stored at fluctuating temperatures.

The cream is best stored at low temperature,
preferably under refrigeration and at constant
humidity. If the cream is packaged in glass or
other moistureproof containers, it can be stored
in refrigerators for long periods, with little
danger of the saturated sirup in the cream
separating.

Fontlaiit

Fondant, a nougat-type candy, is known in
Ohio as maple cream because of its very fine
crystalline character. Fondant is made in ex-
actly the same manner as maple cream except
that the sirup is heated to a higher boiling
point (27° F. above the boiling point of water).
The thickened sirup is cooled to 50° and stirred
as for creaming. Since there is less sirup left in
the fondant, it will set up to a soft solid at room
temperatures. Small amounts can be dropped
on marble slab, waxed paper, or a metal sheet;
or it can be packed into molds.

Sofl Sn^ar ('.an<lu's

Next to maple cream the making of soft
sugar candies is gaining in popularity. Like
maple cream, 8 pounds of soft sugar candies
can be made from 1 gallon of sirup.

Soft sugar candies contain little or no free
sirup, so they are stiffer than maple cream. The
crystals in soft sugar candies are larger than in
maple cream and are palpable to the tongue,
but they should not be large enough to produce
an unpleasant sandy effect. The candies can be
made from any of the top three grades of sirup:
U.S. Grade AA (Fancy), U.S. Grade A (No. 1),

MAPLE SIRUP PRODUCERS MANUAL

101

Figure 110. — The finished or remelted cream is suffi-
ciently fluid to be poured into containers. Use of wide-
mouthed jars makes filling and emptying easy.

and U.S. Grade B (No. 2). Unlike maple cream, a
small amount of invert sugar is desirable be-
cause it reduces the tendency to produce large
crystals that give the candies a grainy texture.
The invert sugar content can be increased by
adding (1) a doctor solution consisting of 1 pint
of dark sirup to 6 gallons of table grade maple
sirup, or (2) a doctor consisting of Vo teaspoon of
cream of tartar to 1 gallon of low invert sirup.
Use the quick test for invert sugar to check the
sirup to be used for candymaking.

Cooking. Cooling, and Stirring

The sirup is cooked to 32° F. above the boiling
point of water established for that time and
place (fig. 111). The pans of cooked sirup should
be cooled slowly on a wooden-top table to
155° F. (as tested with a thermometer). The
thick sirup should then be stirred, either by
hand with a large spoon (fig. 112) or with a
mechanical mbcer.

While the sugar is still soft and plastic, it is
poured or packed into rubber molds of different
shapes. Packing the molds is best done with a
wide-blade putty knife or spatula (fig. 113).

Rubber molds for making candies of different
sizes and shapes can be purchased from any
maple equipment supplier. Before use, the
molds should be washed with a strong alkali
soap, well rinsed, and dried. They should then
be coated with glycerin applied with a brush.
Excess glycerin is removed by blotting with a
soft cloth. If the rubber mold contains too much
carbon, it will make a mark on the molded
sugar. To test for too much carbon, rub the
mold on white paper.

The Bob. — Another method of preparing the
sugar so that it can be run into the molds is
that used by commercial confectioners. After
stirring, the soft sugar is set aside for a day to
firm and age. The following day it is mixed with
an equal amount of "bob," and the mixture is
run into the rubber molds while it is still fluid.

The bob (Si ) is sirup that is boiled to exactly
the same boiling point as used in making the

Figure HI. — Many types of kettles may be used for
cooking the sirup for making soft sugar candies. Where
high-pressure steam is available, a steam-jacketed ket-
tle is ideal since it permits cooking the sirup without
danger of scorching.

102

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

soft sugar (32° F. above the boiling point of
water). As soon as the bob is made and while it
is still hot, the sugar made the previous day is
added to it, and the mixture is stirred enough
to get uniformity but not enough to cause it to

PN_4«0K

Figure 112. — The thick supersaturated sirup is stirred
until sugar crystals form and grow large enough to be
palpable but not large enough to be gritty.

PN-1K09

Figure 113. — The partly crystallized sirup is packed into
molds while it is still plastic. In a few hours crystalliza-
tion is complete, and the candies are firm and can be
removed from the molds.

set up. The hot bob partly melts the sugar, and
the resulting semiliquid sugar can be poured
easily.

Semicontinnous Process. — Ingenuity can be
used in candymaking. For example, one pro-
ducer has developed the following semicontin-
nous process: The sirup is cooked in a special
vessel (fig. 114) from which the cooled sirup is
dispensed to a small mechanical agitator (fig
115).

Here the sirup is partly crystallized, and
while it is still fluid it is run into the rubber
molds where crystallization is completed. It sets
up in 30 minutes to 1 hour. Candies formed by
IX)uring rather than packing have an attractive
glazed surface.

Crystal Coating

Candies can be prevented from diying by
coating them with a moisture-impervious shell
made from crystalline sucrose (99). The effect of
ciystal coating soft sugar candies is shown in
figure 116. The crystallizing sirup is made as
follows: Fancy maple sirup low in invert sugar
is heated to 9.5° to IT F. above the boiling point
of water. This supersaturated sirup should
have a Brix value of 70P to 73" at a temperature
of 68^ and 63.5' Brix at 210^ (hot). One gallon of
standard-density sirup (66° Brix) will make 7
pints of ci-ystallizing sirup (70^ to 73" Brix).

The hot, heavy sirup can be set aside to cool
where it will not be disturbed by jarring or
shaking, or it can be transferred immediately to

PN-4H10

igure 111,. — A special candy-cooking kettle has one end
shaped like a funnel and is provided with a spout and
shutoff. After the cooked sirup has cooled but while it is
still fluid, the kettle is mounted in an upended position
and the sirup is run out through the shutoff. (Cooker
designed by Lloyd H. Sipple, Bainbridge, N.Y.)

MAPLE SIRUP PRODUCERS MANUAL

103

PN-1811

Figure 115. — A continuous candy beater of simple desig^i.
The cooked sirup is run in a small stream from the
cooking kettle to the beater, which consists of a rotat-
ing worm in a metal trough. The worm beats the sirup,
crystallizes it, and then drives the semiliquid sirup to
the drawoff cock that controls the flow of the sirup into
the molds. {Beater designed by Lloyd H. Sipple, Bain-
bridge, N.Y.)

large crystallizing pans. To retard surface crys-
tallization (caused by rapid cooling of the sur-
face), the sirup should be covered with a piece
of damp cheesecloth or paper (preferably the
same kind used as a sirup prefilter, since it has
a high wet strength). The cloth or paper must
be in contact with the entire surface of the
sirup. If crystals form, they will attach them-
selves to this cover and can be removed along
with the covering. The sugar crystals can be
recovered by rinsing the cover in hot water.

The candies to be coated should be dry (24
hours old). They can be coated by either of two
methods. In one method, the candies are loosely
packed two or three layers deep in a tin pan,
such as a bread tin, which has a piece of V2-
inch-mesh hardware cloth in the bottom. The
covering is removed from the cool (70^ to 8(F F.)
crystallizing sirup, and any crystals not re-
moved with the cover are skimmed off.

In the other method, the candies are loosely
placed in wire mesh baskets of such size as to
permit submerging both the baskets and the

PN^812

Figure 116. — Crystal-coated candies: Left, Freshly made,
uncoated candies; center, uncoated candies that have
been stored 3 months at room temperature — the unat-
tractive appearance is caused by drying; right, these
candies, made at the same time as those in the center,
were coated with sugar crystals, which prevented loss
of moisture. They have kept the appearance and char-
acteristics of fresh candies.

dried candies below the surface of the crystal-
lizing sirup (figs. 117 and 118). A fresh cover is
placed directly on and in contact with the entire
surface of the sirup and left at a temperature of
65" to 80P F. for 6 to 12 hours, or overnight. This
is the crystallizing period. The major part of
the ci-ystal coat forms on the candies during the
first few hours. Therefore, the time the candies
are left in the crystallizing sirup beyond a 6-
hour period is not too critical. Actually, the
most important factor is the Brix value of the
crystallizing sirup; if too high, coarse crystals
result. Sugar comes out of the thick sirup and is
deposited and grows on the millions of tiny
crystals on the surface of the candies. The best
density of the sirup should be determined by
trial runs. When sufficient sugar has been de-
posited on the candies, the paper or cloth cover
is removed, and the wire baskets of coated
candies are lifted out of the sirup and supported
above the trays of sirup until the candies have
drained.

104

AGRICULTURE HANDBOOK I'M, U.S. DEPT. OF AGRICULTURE

PN-4813

Figure 117. — A french-fryer blanching assembly pro-
vides a practical means for crystal coating maple candies
on a small scale. The candies are placed in the basket for
crystallizing in the thick sirup and are left in the basket
to drain. The drained sirup is caught in the sirup pan
and is used for making other lots of candies.

PN-4814

Figure 118. — A large crystallizing pan for use in a con-
stant-temperature cabinet. Hangers are attached for
suspending baskets for draining candies after crystal
coating.

After the sirup has drained from the candies
(one-half hour), the candies are dried by remov-
ing all remaining drops of sirup. Failure to do
this results in areas having a glazed (noncrys-
talline) surface that is not a water barrier and
that permits the candies to desiccate (dry out)
during storage. Desiccated spots appear as
vk^hite areas.

The drained candies can be freed of any
remaining drops of crystallizing sirup by two
methods. In one method the candies are spread
out (one layer thick) on a sheet of paper and
each piece is turned over at intervals of 1 to 2

hours. In the other method each piece of candy
is wiped with a damp sponge to remove any
moist areas. The dry candies are placed on
trays (fig. 119); the bottoms of the trays are
made of V4-inch hardware cloth. The trays of
candies are set in racks to complete the air-
drying process at room temperature. This usu-
ally requires from 4 to 7 days. After drying, the
candies are ready for packaging. Candies
should not be crystal coated on humid or rainy
days because they will not diy properly. If
candies are not thoroughly dried, their coating
will dissolve when they are packaged.

The packages have two functions: (1) To
make the candies as attractive as }x)ssible and
(2) to keep them in good condition (fig. 120).
Boxes, individual wrappings, and candy cups
can be obtained from a confectioner's supply
house. The net weight of the candies must be
stated on the outside of the package. This
requires that the weight of the box (tare) and
the net weight of the candies be determined for
each box.

Candies that have been crystal coated have
relatively good shelf life; they do not tend to
take up moisture or to dry out. Candies that are
not crystal coated may do either, depending on

PN-4815

Figure 119. — After the candies have teen removed from
the cr>-stallizing sirup and wiped, they are put on wire
screen trays and placed in racks for air drying before
packaging.

MAPLE SIRUP PRODUCERS MANUAL

105

Figure 120. — Packaging sugar candies, a popular confec-
tion often used as one of the items in a gift package.

the humidity of the room in which they ai'e
stored. In a room of low humidity, they will lose
moisture. The dried-out areas will appear as
white spots and will become stonelike in hard-
ness. If the humidity is high, the candies will
take up moisture, and moist areas or droplets of
water will appear on the surface. The droplets
become dilute sugar solutions and are good
sites for mold growth. The humidity of the
packaging room can be controlled by a de-
humidifier and air-conditioner. Never package
on rainy days (62).

The best type of wrapper for the outside of
the candy package is one that is moistureproof,
such as metal foil or wax-coated paper. A mois-
tureproof wrapper helps to prevent changes in
the candies during storage. Unfortunately,
most wrappers are not completely moisture-
proof.. They reduce the gain or loss of moisture
but do not prevent it, especially if the candies
are stored under excessively high or low mois-
ture conditions or for long jieriods. Some pack-
ers of maple confections obtain longer storage
by puncturing the moistureproof wi-apper with
many small holes to permit the package to
breathe.

Maple S|u-«'iul

Maple cream, described on page 98, is not
stable when stored at room temperature be-
cause saturated sirup (mother liquor) tends to
separate from the cream and cover it with a
sirup layer.

A new semisolid dextrose-maple spread has
been developed that prevents this separation of
sirup. Also, it requires no heating or stirring.

The process for making the spread consists of
three simple steps: (1) The sirup is concentrated
by heating it to a density of 70P to 7S Brix; (2)
part of the sucrose is converted to invert sugar
by enzymatic hydrolysis; and (.3) the dextrose
(part of the invert sugar) is ciystallized to form
a semisolid spread.

Standard-density maple sirup (66° Brix) is
heated to about 1(F F. above the boiling point of
water (approximately 7(? Brix), and then cooled
to 15(F or below (as tested with a thermometer).
While the sirup is still fluid, invertase is added
at the rate of IV2 ounces per gallon of sirup and
thoroughly mixed with the sirup by stiiTing.
The enzyme will be inactivated and hence inef-
fective if it is added while the sirup is too hot
(above 16(F F.). The enzyme-treated sirup is
stored at room temperature for 1 or 2 weeks. At
first, ci-ystals (sucrose) appear, but they do not
form a solid cake, and as the hydrolyzing action
of the enzyme progresses, the crystals dissolve.
The result is a crystal-free, stable, high-density
sirup (70° to 78° Brix) containing a large
amount of invert sugar. This sirup will remain
clear at ordinary temperatures. Because of its
high density, it makes an excellent topping for
ice cream and sirup for waffles or pancakes.

Maple spread is made by seeding this high-
density sirup with dextrose crystals. A crystal-
line honey spread, a stock grocery item, is a
convenient source of dexti'ose crystals for seed-
ing the first batch. For additional batches, crys-
tals from previously made lots of the maple
spread may be used as seed. The dextrose
crystals are added at the rate of 1 teaspoon per
gallon of high-density sirup and thoroughly
mixed with the sirup. After mixing, the sirup is
poured into packages and set aside at a temper-
ature of 55° to 60P F. Within a few days a
semisolid spread forms. It is stable at tempera-
tures up to 8(F F. If refingerated, it will keep
indefinitely without any sirup separating.

Maple spread eliminates the laborious hand
beating or the expensive machine beaters re-
quired for making maple cream. Furthermore,
the yield of maple spread j^er gallon of sirup is
higher, because it is made from sirup concen-
trated to between 7(F and 78° Brix, whereas

106

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

sirup for maple cream is concentrated to 8(F
Brix.

I liin<Ml Mapl<> IVoiliirl

In making tlie maple products described in
the preceding pages, only sirup low in invert
sugar should be used, except for that used as a
doctor. These products, therefore, are primary
uses for the top grades of table sirup, U.S.
Grade AA, U.S. Grade A, and U.S. Grade B.

A new maple product called fluff has been
developed at the Eastern Regional Research
Center (135). It can be made from the lower
grades of sirup (sirup high in invert sugar). In
addition, it has a number of other advantages.
Some of these advantages are: (1) There is a
large overrun because the volume of the cooked
sirup is increased by incorporating air during
the beating process; (2) the new product con-
tains a higher percentage of water than does
maple cream so that a larger volume can be
made from 1 gallon of standard-density sirup;
(3) the monoglyceride used in the formula tends
to reduce its apparent sweetness and make it
more palatable, but without loss of the maple
flavor; and (4) the time required to whip it is
only a fraction of that required for making
maple cream. The fluffed product has excellent
spreading properties and has an impalpable
crystal structure. While there is less tendency
for the fluff to bleed, it does tend to become
somewhat grainy, especially if stirred too long.
This tendency to grain is retarded by storing
the fluff under refrigeration.

Makhtfi ihf Fluff From Maplf Siriii>

Heat the sirup until its temperature has been
elevated 17° F. above that of boiling water.
Allow it to cool, with occasional stirring, to
between 17.5° and 185° F. (as tested with a
thermometer). Add highly purified monoglycer-
ide (Myverol 18-00)^ equal to 1 percent of the
weight of the maple sirup used, that is, 0.11
pound (Va cup) per gallon or 2 level teaspoonfuls
per pint. Dissolve the monoglyceride by adding
it slowly and stirring. If the sirup cools below
145°, the monoglyceride will not dissolve. Cool to
between 150P and 160^ and whip the mixture

' Produced by Distillation Products Industrj'. Roches
ter, N.Y.

with a high-speed (household) beater. Fluffing
should occur within 2 minutes.

\hikiiifi thf Fluff From Mofflf .Sin/;* nnti
Moith' Sufior

To 1 cup of pure maple sirup (any grade) add
V2 cup of maple sugar and heat the mixture
until the sugar is completely dissolved. Do not
boil. Cool to between 175° and 185° F. with
occasional stirring. Add slowly and stir until
dissolved 1 teaspoonful of Myverol 18-00 for
each cup of sirup. Cool to between 15(f and 16(F,
and whip the mixture with a high-speed (house-
hold) beater. Fluffing should occur within 2
minutes.

The sugar must be completely in solution at
the time it is whipped to prevent a grainy
texture. If sugar crystals do form, they may
be redissolved by heating the suspension; but
loss of water must be avoided, and no more
Myverol need be added.

Excessive heating of the Myverol tends to
cause it to lose its properties.

The texture and consistency of the fluffed
products can be varied as follows:

(1) Whipping Time. — As time of beating
lengthens, the stiffness of the product in-
creases. The initial, thin whip can be used as a
topping for ice cream or other desserts. The
stiffer product is an excellent spread or icing for
baked goods. (The beating time will be affected
by the temperature of the mixture at the start
of the beating. The higher the temperature, the
longer it will take to reach a given consistency.)

(2) Ratio of Sugar to Wafer.— The higher the
sugar content of the mixture in relation to the
water content at the time the sugar-water-
stabilizer mixture is whipped, the greater the
consistency of the fluffed product.

Hi^li-Fla>or<Ml MapK* Sirup

As stated earlier, the color and flavor of
maple sirup result from a type of browning
reaction that occurs between constituents of
the maple sap during evaporation. Experiments
have shown that all the potential flavor is not
developed during the usual evaporation proc-
ess. {1J,8). To develop maximum flavor, the
browning reaction must be carried further; that
is, the sirup must be heated to a higher temper-
ature and for a longer time.

MAPLE SIRUP PRODUCERS MANUAL

107

Unfortunately, high temperatures favor the
formation of an acrid "caramel" flavor. The
presence of large amounts of water favor cara-
mel formation and the presence of some cara-
mel in the initial sirup accelerates it (90). There-
fore, only the two top grades of sirup — U.S.
Grade AA (Fancy) or U.S. Grade A (No. 1)—
should be used in making high-flavored maple
sirup. It may be made by the atmospheric
process (H9), by the constant-volume pressure-
cooking process (139)? or by the new continuous
process.

High-flavored maple sirup made from U.S.
Grade AA or U.S. Grade A sirup by either
process will have a strong full-bodied flavor
four to five times that of the sirup from which it
was made, and it will be essentially free from
caramel.

The high-flavored process does not concen-
trate the flavor; instead, it develops more ma-
ple flavor than present in the original sirup.

Atmospheric Process

In the atmospheric process the sirup is con-
centrated at atmospheric pressure by heating
to a boiling temperature of 25(y to 255° F. This
reduces the water content of the sirup to ap-
proximately 10 percent. The sirup is held at this
temperature for IV2 to 2 hours. It is then cooled,
and water is added to replace that lost in
evaporation so that the sirup is again of stand-
ard density.

Because of the low moisture content of the
sirup during the cooking period, there is danger
of scorching if it is heated in a kettle on a stove
or other hot surface. It is recommended, there-
fore, that the high-flavoring process be con-
ducted with high-pressure steam in a steam-
jacketed kettle or in a kettle provided with a
steam coil (chart 22).

The first step of the process — removing the
water from the sirup — should be done as rai>
idly as possible. Steam pressure of from 30 to
1(K) pounds should be used. As soon as the sirup
reaches a temperature of 252" F., the steam
pressure is reduced until only enough heat is
applied to maintain the sirup between 25(P and

TRAP

DRAIN

STEAM OR WATER
CONNECTION

" Described in U.S. Patent 2,054,873 issued to George S.
Whitby on September 22, 1936. This patent has expired,
and the process is now available for free use by the
public.

Chart 22. — Kettle with steam coil can be built in any tin
shop. It is not as convenient to use as a tilting-jacketed
kettle, but very satisfactory results can be had with it.
Like the steam-jacketed kettle it must be operated with
high-pressure steam and the condensed water must not
be allowed to collect in the coils. Provision should be
made for running cold water through the coils for
cooling the sirup.

255°. Usually a steam pressure of 20 to 28
pounds is sufficient. A cover is placed over the
kettle to prevent further loss of water through
evaporation. The cover need not be airtight.
Because of the high viscosity of the sirup, little
water will be vaporized.

A thermometer calibrated in 1° intervals,
with a range that includes 250^ to .30(f F., is
kept in the sirup during the high-flavoring
process. If the temperature of the sirup rises
above 255° during the holding period, the steam
pressure should be decreased. To prevent for-
mation of crystals, the sirup should not be
stirred or agitated during the high-flavoring
process.

The end of the heating (cooking) period is
best determined by odor. The cover is lifted, and
a handful of steam is scooj^ed up and brought
toward the nose; heating is stopped as soon as
an acrid caramel odor is detected in the steam.
Care must be taken not to get a steam burn.

108

AGRICULTURE HANDBOOK 184. U.S. DEPT. OF AGRICULTURE

Always bring the hand to the nose; do not bend
over the kettle.

At the end of the cooking period, the thick,
supersaturated sirup is cooled to I8(f F. Ap-
proximately 3 pints of water is added for each
gallon of sirup originally used to replace the
water lost in evaporation and restore the sirup
to standard density. Extreme caution must be
exercised in adding the water because the
water will be converted to steam with explosive
violence if the sirup has not cooled to a temper-
ature below the boiling point of water.

After addition of the water, the sirup is again
brought to a boil and heating is continued until
the temperature reaches that of standard-den-
sity sirup (7 F. above the boiling point of
water).

As flavor and color in sirup develop initially
to the same degi'ee, flavor development in the
treated sirup may be measured indirectly by
measuring the increase in its color. A sample of
the high-flavored, standard-density sirup is
weighed and then diluted with a colorless cane
sugar sirup having a density of 66° Brix as
measured with a hydrometer or refractometer.
The colorless sirup is added slowly to the high-
flavored sirup, with thorough stirring, until the
mbcture matches the color of the original maple
sirup. Then the mixture is weighed. The in-
crease in color and flavor is determined by the
ratio.

Weight of mixed sirup

Weight of high-flavored sirup

= Increase in flavor

This procedure can be used to follow the
progi-ess of the high-flavoring process, since
different lots of sirup of the same grade develop
flavor at slightly different rates. A sample is
removed periodically from the cooking sirup
and weighed. Enough water is added to restore
the sample to standard density (66' BrLx), and
its increase in color and flavor is determined.
The tests are easy to make; the 2-ounce French
squai-e bottle supplied with the U.S. color com-
parator (described on p. 89) is used. The high-
flavor process and its end uses are shown in
figure 121.

l'rfssiir<'-( DoLiiifi I'rnifss

Many maple producers do not have higli-
pressure Steam equipment. They may make

A NEW MAPLE PRODUCT

■IJ^

PN"-48n

Figure 121.— A schematic drawing showing the high-
flavoring process and its use in making blended sirup
and as a food flavoring.

high-flavored sirup by the pressure-cooking
process {139}. In this process, standard-density
sirup is heated in a closed vessel, such as an
autoclave or ordinaiy pressure cooker, at 15
pounds' pressure. Best results are obtained
when the sirup is heated to a temperature of
25(f to 253° F. as in the atmospheric process.

In the pressure-cooking process, the water
content of the sirup is 34 percent during
heating rather than 10 percent, as in the at-
mospheric process. The higher water content
favors formation of caramel. However, the rate
at which caramel forms depends on the original
caramel content of the sirup. The higher the
caramel content in the original sirup, the
greater the amount formed in the product.
Since the amount of caramel in sirup is related
to the amount of color, only U.S. Grade AA
(Fancy) or U.S. Grade A (No. 1) sirup should be
used to make high-flavored sirup by the pres-
sure-cooking process. Darker grades usually re-
sult in an unpalatable product.

The sirup is heated almost to boiling and
immediately is transferred to jars, which are
filled to vvithin '., inch of the top. The lids are

MAPLE SIRUP PRODUCERS MANUAL

109

set loosely in place, and the jars are placed in
an autoclave or pressure cooker, which contains
the amount of water specified by the manufac-
turer. The cover of the cooker is assembled, and
steam is generated accordinfi: to the manufac-
turer's directions. The sirup is heated at 1.5
pounds' pressure for approximately VI., hours.
Then the pressure is decreased slowly to zero
without venting or quenching. The containers
must not be jarred or the sirup may boil over.

( .s«>.s' «»y ftifih-h'hit'ored Siriift

High-flavored sirup has a number of uses.
Because it is richer in maple flavor, it is ideal
for making maple products. It is especially de-
sirable for use in making cream and candies.
From 1 to 2 percent of invert sugar is formed in
the high-flavoring process. This is the optimum
amount to make perfect cream or soft sugar
candies without the need of a "doctor." High-
flavored, high-density maple sirup makes a su-
perior topping for ice cream.

Only high-flavored sirup should be blended
with other foods such as maple-flavored honey
and crystalline honey spreads. Regular maple
sirup usually does not have enough flavor to
compete with or to break through the flavor of
the food to which it is added. An inexjjensive
table sirup that has the full flavor of pure
maple can be made by blending 1 part of high-
flavored, standard-density sirup with 3 parts of
cane sugar sirup that has a Brix value of 66°.
Blended sirup must be projDerly labeled when
offered for sale. The percentage of each ingi-edi-
ent must appear on the label, with the one in
greater amount appearing first.

drvslalliiK' Moncv-Miipli- Spix'ad

The development of a maple-flavored crystal-
line honey spread has produced a new farm
outlet for both maple sirup and honey. This
spread is made by mixing honey with high-
flavored maple sirup {81 ). The maple flavor
must be strong enough to break through the
honey flavor and tiie siruj) must contain a large
amount of invert sugar. These requirements
are met by converting U.S. Grade B (Vermont
B or New York No. 2) sirup to high-flavoretl
sirup as described earlier except that the siruj)
is heated to a temperature W or 2(f F. above
the boiling point of water. It is then cooled to

150P or lower, and V/., to 2 ounces of the enzyme
is added i^er gallon of sirup. The mixture is set
aside at room temperature until the action has
been completed, usually about 2 weeks. The
sirup may have the appearance of soft sugar
(U5).

The high-flavored, high-density maple sirup
is added to mild strained honey at the rate of 33
parts of maple sirup to 67 parts of honey by
weight. The mixture is crystallized by the Dyce
process (21) as follows: The honey-maple mix-
ture is seeded with crystalline honey (available
in most gi'ocery stores) or with some honey-
maple spread from a previous batch, at the rate
of 1 ounce of seed to 1 quart of honey-maple
mixture. After thorough stirring, the seeded
mixture is held at 57° to BOF F. until crystalliza-
tion is complete, usually 3 to 7 days. The result-
ing product is smooth, it has a barely percepti-
ble gT'ainy character, spreads well, and has a
very pleasing flavor. This spread becomes liquid
at temperatures above 85°. Therefore, it should
be stored under refrigeration.

Maple sirup blends well with honey in mak-
ing other honey-maple confections. Recipes for
these can be obtained from Pennsylvania State
University, University Park, Pa. 16802.

Other Mapir l*ro<liuts
Rock Cdinly

Production of rock candy usually is uninten-
tional. Although it should not be considered a
product of maple sirup, this form of "maple
sugar" is easy to make, as follows: When maple
sirup is evaporated to a density between 67.5°
and 7(f BrLx (heated to ST F. above the boiling
point of water), and the sirup is stoi'ed for a
considerable length of time at room tempera-
ture or lower, a few well-defined crystals of
sucrose (rock candy) appear. These continue to
grow in size if the sirup is left undisturbed for a
long time.

Hard Siignr

Because it is not easy to eat, hard sugar is
not classified as a confection. Producers find
there is a small demand for hard sugar since it
offers a convenient form for the safe and stable
storage of maple sirup. The hard sugar cake
can be broken up and melted in water, and the

110

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

solution can be boiled to bring it to sirup den-
sity. This sirup is called maple-sugar sirup to
distinguish it from sirup made directly from
sap.

Hard sugar is made by heating maple sirup
to approximately 40P to 45° F. above the boiling
point of water. As soon as the sirup reaches the
desired temperature, it is removed from the
heat and stirred. Stirring is continued until the
sirup begins to crystallize and stiffen; then the
semisolid sirup is poured into molds. If stirring
is continued too long or if transfer of the sugar
to the molds is delayed, the sugar will solidify in
the cooking vessel.

In the past, hard sugar, often called maple
"concrete," was the preferred form for holding
commercial maple sirup in storage.

Granulated (Stirred) Sugar

Granulated (stirred) sugar is made by heat-
ing maple sirup to between 40P and 45° F. above
the boiling point of water, as in making hard
sugar. The hot, partly crystallized, thickened
sirup is transferred from the kettle to a stirring
trough, and it is stirred continuously until
gi-anulation is achieved. In the past, this form
of maple sugar was made by stirring it in a
hollowed log usually made from basswood (fig.
122).

Maple on Snoiv

Maple on snow is a favorite of guests at a
maple-sirup camp. As in making stirred sugar,
the sirup is heated to 22^ to 4(f F. above the
boiling temperature of water. The final temper-

PN-IKIK

Figure 122. — Stirred sugar, another popular item, while
more easily made by stirring the sirup in a steam
kettle, has often been made by stirring it in a hollowed-
out basswood log with a wooden hoe.

ature within this range depends on individual
preference. As soon as the sirup reaches the
desired temperature, it is poured immediately,
without stirring, on snow or ice. Because it
cools so quickly, the supersaturated solution
does not have a chance to crystallize; it forms a
thin, glassy, taffylike sheet.

Recipes for other maple confections can be
obtained by writing to your State Department
of Agriculture or your Extension Service.

Suimnai'^

Maple Sugar

(1) Converting maple sirup to maple sugar is
not difficult. The only special equipment
required for small-scale operations is a ther-
mometer having an upper range of 250^ to
300P F. calibrated in 1° units.

(2) Sirup that is saturated with sugar at one
temperature will be supersaturated when
cooled to another temperature.

(3) Supersaturated sugar solutions tend to re-
gain their normal or saturated state by
throwing the excess sugar out of solution.
This precipitated sugar usually is in the
form of crystals, and the amount formed
depends on the degi'ee of supersaturation.

(4) The size and number of crystals in the
precipitated sugar depend on the degi'ee of
supersaturation, the rate of cooling the sir-
up, and the amount and time of stirring.

(5) Invert sugar, a product of sucrose, tends to
retard the crystallization. Its presence in
maple sirup is usually the result of fermen-
tation of the sap. It influences the ciystalli-
zation of maple sugar. Too much invert
sugar may prevent ciystallization of sugar
from a supersaturated sirup. Too little will
cause the maple sugar to be coarse and
gritty.

Maple Cream or Butler

(1) Use a sirup low in invert sugar (0.5 to 2
percent). U.S. Grade AA (Fancy) or U.S.
Grade A (No.l) usually meets these specifi-
cations.

(2) Test all sirup for invert sugar by the quick
test. Do not use sirup that contains more
than 4 percent of invert sugar.

MAPLE SIRUP PRODUCERS MANUAL

111

(3) Heat the sirup to 22 or 2-f F. above the
boihng: point of water.

(4) Cool the sirup rapidly to 5(T F.

(5) Stir the thickened sirup continuously until
creaming: is completed.

(6) Freshly made cream can be packed immedi-
ately or it can be aged before packajering.

(7) Aged cream can be softened for pouring by
heating to a temperature not exceeding
15a F.

(8) Store the cream under i-efrigieration.

(9) Causes of failure to cream:

(a) If the sirup contains too little invert
sugar or if it is not chilled sufficiently
before stirring, the cream will have
gi'itty texture.

(b) If the sirup contains too much invert
sugar, it will not cream (crystallize).

FontUiitl

(1) Pi-epare as for maple cream, except increase
the boiling point of the sirup to 2T above
that for water.

(2) Stir or beat the sirup as for maple cream.

(3) Place drops of the semisolid sugar on mar-
ble slab, waxed paper, or metal sheet — OR —

(4) Pour the semisolid sugar into rubber molds.

Soft Sn^iir ('(indies

(1) Use any of the top three grades of sirup.

(2) Heat the sirup to 32" F. above the boiling
point of water.

(3) Cool the sirup slowly to 155= F.

(4) Stir the thickened sirup until enough ciys-
tals have formed to make a soft, plastic
mass.

(5) Immediately pour or pack the soft sugar
into molds — OR —

(6) Set it aside in a crock at room temperature
for 24 to 48 hours.

(7) Concentrate an equal amount of sirup as
before.

(8) As soon as the same elevation of boiling
point (32° F.) is reached, add the hot concen-
trated sirup (bob) to the aged soft sugar.

(9) Stir only enough to mix and pour the semi-
solid sugar into the molds.

Crystdl Cnatiiifi

(1) Make crystallizing sirup from top grades of
maple sirup.

(2) Concentrate the sirup to a density of l(f to
7.T Brix by heating it to 9.5" or IT F. above
the boiling point of water (63.5° Brix hot
test).

(3) Cool to room temperature.

(4) Keep the surface of the sirup covered with
heavy paper, except when adding or remov-
ing the candies.

(5) Place the freshly made candies in the heavy
sirup and leave them in the sirup 6 to 12
hours.

(6) Remove the candies and completely drain
the sirup from them.

(7) Place the candies on paper-covered trays
and turn each piece eveiy hour until diy, or
wipe with a damp sponge.

(8) Do not attempt to crystal coat candies dur-
ing humid or rainy weather.

(9) Air diy at room temperature 4 to 7 days.

Maple Spreiiil

(1) Use any of the three top grades of sirup.

(2) Heat the sirup to 10= or ir F. above the
boiling point of water (7Cf to 78" Brix).

(3) Cool the thick sirup to 150P or below and add
IV2 ounces of invertase per gallon of sirup.

(4) Store at room temperature for 2 weeks. The
resulting product is high-density sirup.

(5) "Seed" the high-density sirup with dextrose
crystals from previous batches of spread or
from ciystallized honey. Use 1 teaspoonful
per quart of sirup.

(6) Mix the seed thoroughly through the sirup
and pour the mixture into the final package.

(7) Store at 55= to 60F F. Within a few days the
dextrose ciystals will grow to yield a plastic
spread.

Fltiffed Maple Proditvt

(1) Can use lower grades of sirup.

(2) Heat the sirup to IT F. above the boiling
point of water.

(3) Cool with occasional stirring to 175° to
185° F.

(4) Add 1 percent (Vs cup per gallon or 2 level
teaspoonfuls per pint) of a purified monogly-
ceride (Myverol 18-00) slowly with stirring.

(5) Cool to 150f to 160F F., whip 2 minutes with
a high-speed cake mixer.

112

AGRICULTURE HANDBOOK 184, U.S. DEPT. OF AGRICULTURE

Hifili-h l<iitfrt'«l Mtiplf Sirup

Use either of the two top grades of sirup to
make hig:h-flavored maple sirup, and make it by
either the atmospheric or the pressure-cooking
process.

Atmospheric Process

(1) Concentrate the sirup by heating to 40P F.
above the boiUng point of water (25Cf to
255" F.). Pi'ocess only in a steam kettle, jack-
eted or with coils.

(2) Hold the thickened sirup at the final tem-
perature of concentration for IV2 to 2 hours.

(3) Cover the kettle and reduce the steam pres-
sure to approximately 24 or 26 pounds per
square inch — to keep the sirup at 252" to
255° F.

(4) Turn off the steam at the end of the proc-
essing period and cool the thick sirup to
180F F.

(5) Add water with caution and in small
amounts until the sirup is restored to about
standard density and reboil to T F. above
the boiling point of water.

Pressure-Cooking Process

(1) Heat the sirup almost to boiling tempera-
ture (210F to 215= F.).

(2) Transfer to containers to fit the cooker (usu-
ally 1- or 2-quart jars).

(3) Place the lids on the containers loosely, and
put them in the cooker.

(4) Add water to the cooker according to the
manufacturer's directions and secure the
cooker lid.

(5) Bring the steam pressure in the cooker to
15 pounds per square inch. Hold at this
pressure for V/2 hours.

(6) Allow the pressure to fall slowly; do not
vent or quench.

(7) When the pressure has fallen to zero, open
the cooker and remove the high-flavored
sirup.

(.rvshilliiit' Hiniry- Maplf Sinriiil

(1) Use U.S. Grade B, Vermont B, or New York
No. 2. sirup.

(2) Heat the sirup to 19^ or 2Q F. above the
boiling point of water (80P Brix).

(3) Cool the thick sirup to below 150P F. and add
IV2 to 2 ounces of invertase per gallon of
sirup.

(4) Store at room temperature for 2 weeks to
produce a high-density sirup.

(5) Mix thoroughly one part of the high-density
sirup to two parts of mild flavored honey.

(6) Add seed (dextrose crystals) at the rate of 1
teaspoonful per gallon of mixture. Use a
previous batch of honey-maple spread or
crystalline honey as seed.

(7) Hold the seeded mix at 6(f F. until the
dextrose crystals grow to produce a semi-
fluid plastic (from 3 to 7 days).

(8) Store under refrigeration.

Rock i'.nnily

(1) Use one of the top grades of maple sirup.

(2) Heat the sirup to SP F. above the boiling
point of water (67.5= to 70P Brix).

(3) Store several months at or below room tem-
perature.

Hdrd Sugar

(1) Use any grade of sirup.

(2) Heat the sirup to between 40P and 45° F.
above the boiling point of water.

(3) Remove from the heat and begin stirring
the hot, thick sirup immediately.

(4) Continue stirring until ciystals form (sirup
begins to stiffen).

(5) Pour the partly crystallized sirup into molds
to harden.

Granulated (Stirred) Sugar

(1) Use a top grade of sirup.

(2) Heat the sirup to between 4(f to 45? F.
above the boiling point of water.

(3) Pour the hot sirup immediately into a tray
or trough for stirring.

(4) Begin stirring immediately and continue
stirring until granulation is completed.

Miiplc >ni Slum-

(1) Use the top grades of sirup.

(2) Heat the sirup to between 22= and 4(r F.
above the boiling point of water.

(3) Without stirring, pour the sirup immedi-
ately onto the snow or ice; it will form a
glassy, taffylike sheet of candy.

MAPLE SIRUP PRODUCERS MANUAL

TESTING MAPLE SIRl P FOR IINVERT SUGAR

113

The relation between the invert sugar con-
tent of maple sirup and its suitability for mak-
ing maple cream is as follows:
Invert sugar
content of
sirup (percent) Suitability for cream

0.5 to 2 The right amount of invert sugar

for making a fine-textured
cream — one that feels smooth to
the tongue.

2 to 4 Can be made into cream if sirup is

cooked until it is 2° to 4° F. hotter
than temperature called for in
standard recipes for cream.
4 or more Not suitable for cream. If used, su-
crose will not crystallize, or it will
crystallize only if sirup is heated
to a much higher-than-standard
temperature. Such cream will be
too fluid and probably will sepa-
rate a few days after it is made.

Two tests are available for determining the
invert sugar content of maple sirup. The simple,
or short-cut, test merely shows whether the
sirup contains less than 2 percent of invert
sugar and is therefore suitable for creaming.
The other is a quantitative test. It measures
invert sugar in amounts up to 7 percent, the
upper limit normally found in maple sirup.

Simple Test

The simple test for determining the invert
sugar content of maple sirup has been adapted
from a standard test for determining the sugar
in urine (78, 80). The test is made by first
preparing a sirup-water mixture (1 part of sirup
to 20 parts of water) and then color testing the
diluted sirup. It can be made in 3 or 4 minutes.

Equipment

The few pieces of equipment required to
make the tests can be obtained from the local
pharmacy. The following items are required:

(1) Clinitest tablets'" obtainable at pharmacy.

(2) Two medicine droppers.

(3) A test tube, about V2 inch in diameter and

3 or 4 inches long.

(4) A sample of the sirup to be tested (1
cupful).

(5) One medicine glass, calibrated in ounces.

(6) One glass measuring cup, calibrated in
ounces.

(7) Test tube holder.

(8) Two 8-ounce, clean and dry drinking
glasses.

(9) One 1-quart glass fruit jar and cover.

(10) One "Clinitest" color scale.

(11) Water (20 fluid ounces).

M„ki

tlu- Test

'" Trademark. This product is one of several that may
be used by diabetics in testing for sugar in urine.

(1) Carefully pour enough of the test sirup
into a medicine glass to bring the level of the
sirup exactly to the 1-ounce (2 tablespoons)
mark. If too much (more than 1 ounce) is added,
empty the sirup out of the medicine glass, wash
and dry it, and start over.

(2) Measure 2V2 cups of water and transfer it
to the quart jar.

(3) Make the l-to-20 solution by pouring the
fluid ounce of sirup into the jar containing the
2V2 cups (20 fluid ounces) of water.

(4) Pour some of the water-sirup mixture into
the medicine glass and return it to the jar.
Repeat this three or four times to be sure that
all the sirup has been transferred to the water
in the jar. Mix the contents of the jar thor-
oughly by stirring with a spoon or with a
portable electric mixer.

(5) Place the test tube upright in the holder.
(The holder can be a 1-inch-thick block of wood,
2 inches square with a ''/le-inch hole ^/4 inch
deep.)

(6) Fill a clean, diy medicine dropper with the
diluted (1:20) sirup in the fruit jar. Hold the
dropper upright above the test tube and let 5
drops of the diluted sirup fall into the test tube.

(7) Fill another clean and dry medicine drop-
per with water and add 10 drops of water to the
test tube.

(8) Place a Clinitest tablet, freshly removed
ft'om the bottle or wrapjier, in the test tube. As
the tablet dissolves, it causes the contents of
the tube to boil. Do not remove the tube from .
the holder while the solution is boiling.

114

AGRICULTURE HANDBOOK 184, U.S. DEPT. OF AGRICULTURE

(9) Fifteen seconds after the boiling stops, add
water to the test tube until it is two-thirds
filled.

(10) Observe the color of the solution and
compare it with the two colors marked + and -
of the color scale furnished with the Clinitest
tablets. Disregard everything else on the scale
card. The other colors and the" labels on the
scale card have no relation to this test. Make
the color comparison in a room illuminated with
an incandescent bulb. The colors are not easily
judged by fluorescent or direct sunlight.

Intvritretinfi the Krsiills

Color of Solution in Test lube. — Blue indi-
cates a negative test; the sirup contains less
than 2 percent of invert sugar and can be used
to make cream. Yellow or yellow gi-een indi-
cates a positive test; the sirup contains more
than 3 percent of invert sugar and is not suita-
ble for making cream.

Quantitative Test

The quantitative test is much longer than the
simple test; it requires about 15 minutes.

I'rpparing the Siriiit-Wtiter Mixtures

For this step, you will need sirup, 15 quarts of
water, measuring cup, quart measure, pail or
other large container, long-handled spoon,
small spoon, and five 4-ounce drinking glasses.
The glasses should be thoroughly dry. You will
also need a pencil and labels.

Stir thoroughly the sirup to be tested. Then
fill the measuring cup exactly to the 1-cup mark
with sirup.

Dilute this sirup with five successive addi-
tions of water, as follows:

l-and-1'2 Dilutimi (1 cup of sirup and 12 cups
of water). — Pour 2 measured quarts (8 cups) of
water into the pail. Pour the cupful of sirup into
the pail; let the cup drain until most of the
sirup is out of the cup.

Measure a third quart (4 cups) of water and
use this to rinse the remaining sirup from the
cup; fill the cup with water, stir with a small
spoon, and pour into the pail until the quart of
water is used.

Stir the sirup and water in the pail until it is
thoroughly mixed.

Dip one 4-ounce glass into the dilute sirup
and withdraw half a glassful.

Label the glass "12" and set it aside.

l-and-20 Dilution. — To the dilute sirup in the
pail, add 2 measured quarts (8 cups) of water.

Stir tlie contents of the pail until well mixed.
Remove half a glassful and label it "20."

l-and-32 Dilution. — Add 3 measured quarts
(12 cups) of water to the mixing pail. Stir
contents until well mixed. Remove half a glass-
ful and label it "32."

l-and-40 Dilution. — Add 2 measured quarts (8
cups) of water to the pail. Stir contents until
well mixed. Remove half a glassful and label it
"40."

l-and-60 Dilution. — Add 5 measured quarts
(20 cups) of water to the pail. Stir contents until
well mixed. Remove half a glassful and label it
"60."
Color Tesliiifi the Dihitioiis

For this step you will need the labeled sam-
ples of the five dilutions, test tube holder for
five tubes, five test tubes, six medicine drop-
pers, Clinitest tablets and color scale, a small
amount of water, and pencil and paper.

Make the color test as follows:

(1) Place five of the test tubes in the test tube
holder.

(2) Fill a clean, diy medicine dropper with the
diluted sirup from the glass labeled "60." Hold
this dropper upright above the test tube in the
hole marked "60" and let exactly five drops of
the diluted sirup fall into the test tube.

Similarly, place exactly five drops of the "40"
dilution, five drops of the "32" dilution, five
drops of the "20" dilution, and five drops of the
"12" dilution in the tubes numbered for these
dilutions (see fig. 123). Use a separate, clean,
dry medicine dropper for each dilution.

(.3) Fill another clean medicine dropper with
water and add 10 drops of water to each of the
five test tubes, refilling the medicine dropi^er as
necessary.

(4) Remove five Clinitest tablets from the
bottle or wrapper. Place them on a clean piece
of paper.

(5) Place one tablet in each test tube, in order,
starting with the tube marked "60."

The tablets, as they dissolve, cause the con-
tents of the tubes to boil. Do not move the test
tubes while tlie solutions are boiling.

MAPLE SIRUP PRODUCERS MANUAL

115

Figure 123.

PN-1S19
-Testing sirup for invert sugar.

Write down in order the values you have
griven the five dilutions, starting with the 1-and-
12 dilution at the left.

Special Note. — If the first sirup you test
proves positive in some dilutions and negative
in others, you will quickly see the difference
between a positive and a negative color reac-
tion.

It is possible, however, that the sirup you test
will give a positive or a negative test in all
dilutions. If this happens and you ai'e doubtful
about your interpretation of the results, it will
be helpful to have a solution that you know will
give a jx)sitive test.

To prepare such a solution, add three drops of
corn sirup to the 4-ounce glass containing the
sample of the l-and-60 dilution. Stir the com
sirup into the dilute sirup.

In a clean test tube place five drops of this
solution. Add 10 drops of water, then one Clini-
test tablet. After boiling has stopped add water
until the test tube is two-thirds full.

The color that develops will indicate a posi-
tive reaction.

(6) Fifteen seconds after the boiling stops, add
water to the test tube marked "60" imtil the
tube is two-thirds full. Add the same amount of
water to the other four test tubes, in order,
from right to left.

(7) Compare the colors in the test tubes with
the two colors of the color scale marked "trace"
and "-f^". Disregard everything else on the
scale; the other colors and the labels on all the
colors have no relation to this test.

Make this comparison in a room lighted with
an incandescent bulb. You cannot judge the
colors of the solutions for this test with fluores-
cent light or with sunlight only.

Assign to the mixture in each tube one of
three values — positive (+ ) for invert sugar, neg-
ative (-) for invert sugar, or doubtful (±) ac-
cording to the following standard:

Color of solution Value

Same as or more blue than color on scale

labeled "trace" Negative (-)

Same as or more yellow than color on

scale labeled " + " Positive ( + )

Between "trace" and " + " colors on scale Doubtful (± )

Detorniiiiiiig In>ei't Siiftar Content of
Sirup

To find the invert sugar content of the sirup
you are testing, find the line in table 17 that
contains the same combination of values for the
five dilutions that you obtained in the color
test.

As the table shows, the sirups that are most
suitable for making into cream are those that
are negative in all dilutions or positive in the
first (l-and-12) dilution and negative in all the
others.

Suniniaiy

(1) Test the sirup for its invert sugar content
before attempting to make maple cream.

(2) Use the simple or shortcut test, page 113.

(3) To check the color, positive or negative, use
a test .solution consisting of the 1- and 60-
solution to which is added com sirup, page
115. This will give a positive test.

(4) Sirup containing more than 3 percent of
invert sugar is unsuitable for creaming.

116

AGRICULTURE HANDBOOK l.'?4. U.S. DEPT. OF AGRICULTURE

Table 17. — Key for interpretinx) results of color test for invert siigar content of five dilutions of

maple sirup

[- indicates negative reaction; + indicates positive reaction; ♦ indicates doiibtlul reaction!

Reactions for 5 test dilutions

Invert-sugar content of sirup

Suitability of sirup for making into
cream

Percent

Less than 2 Suitable.

More than 2, less than 3 Suitable.

More than 2, less than 4 Suitable if sirup is heated 2 to 4

degrees higher than usual in cream-
making.

More than 3, less than 4 Not suitable.

More than 3, less than 5 Not suitable.

More than 4, less than 5 Not suitable.

More than 4, less than 6 Not suitable.

More than 5, less than 6 Not suitable.

More than 5, less than 7 Not suitable.

Above 6, may be 7 or more Not suitable.

THE CErNTRAL EVAPORATOR I'LAINT

Before 1955 no market existed for maple sap.
The sap crop had to be converted to sirup or
some other product on the farm where it was
produced before it became marketable. Maple
sap, therefore, occupied a unique position in
American agriculture because all other farm
crops are marketable as produced.

This practice contributed little toward devel-
oping the maple industry or toward moderniz-
ing sap production to make it competitive with
dairying, stock raising, or gi-ain farming.

The cuiTent trend toward central evaporator
plants (figs. 124 and 125) has marked a new era
in the maple industry. No longer do all sap
producers have to be skilled sirupmakers; in-
stead, the central plants are operated by and
staffed with specialists not only in sirupmaking
but also in marketing. Other advantages of-
fered by the central evaporator plants are:

(1) The central plant eliminates the former
duplication on each farm of invested capital for
evaporator and related equipment and for an
evaporator house.

(2) The farm plant often was too small to be
operated economically and was wasteful of la-
bor. A small evaporator having an output ca-

pacity of 1 to 5 gallons of sirup per hour re-
quires as many man-hours for its operation as
does the central evaporator plant that produces
15 or more gallons of sirup per hour.

(3) Thousands of farmers with stands of ma-
ple trees that they had not previously used for
sap-sirup production now find it practical and
economical to produce and sell a sap crop.

(4) A more uniform and better quality prod-
uct can be produced in a central plant. This
tends to stabilize the market.

PN-1S20

Figure liJ,. — This central evaporator plant at Ogema,
Wis., has one evaporator.

MAPLE SIRUP PRODUCERS MANUAL

117

Figure 125. — A large central evaporator plant located at
Anawa, Wis. Some plants are large enough to make 20
or more gallons of sirup per hour.

L«>4-atioii

The site for a central plant should be cai-e-
fully chosen. Some of the factors to be consid-
ered are:

(1) It should be centrally located in relation to
the sap-producing farms.

(2) It should be on an improved road, prefera-
bly at an intersection. The road should bear
considerable nonlocal traffic.

(3) It should have adequate space for drive-
ways for delivery of sap.

(4) It should have an access roadway from the
main road and off-road parking areas for visi-
tors (customers).

Size

Like other industries, the size of the central
evaporator plant will be governed by a number
of factors that can readily be determined. Un-
like other industries, the central plant can eas-
ily be expanded to accommodate increased de-
mands because of the relative simplicity of
equipment and plant design.

The initial plant must be large enough so
that the volume of sirup produced will yield
reasonable returns on the invested capital and
so that labor will be used economically. These
two factors will be determined by the cost of the
sap, the number of hours per day the plant is
operated and the length of the season, the

number of man-hours required to operate the
plant, the output, and the price of the finished
product. These factors, in turn, depend on the
size of the evajwrators, the density f Brix) of
the sap, and the efficiency of the plant.

Since the plant handles liquids (sap and sir-
up), it can be completely automated. The extent
of automation will be governed by the size of
the i)lant and the budget. The cost of producing
a gallon of sirup decreases as plant size in-
creases.

An evaporator plant building of shed roof
design permits easy expansion. The shed roof
building can be doubled in size by adding three
walls to convert it to a gabled roof building. The
building must be large enough to permit easy
access to the evaporators and other equipment.
The materials should be easy to clean, such as
concrete floors, smooth walls, and built-in cup-
boards and resti-ooms. Provision should be
made for a candy kitchen and a salesroom.

The most common type of central evaporator
plant uses oil heat to evaporate the sap in tlue
pans, each of which is independently installed
on its own arch with its own oil burner (see p.
59). A coil or tube of high-pressure steam is
used to heat the finishing pan, which is also
mounted on its own support (fig. 126 and chart
23).

PN-1822

Figure 126. — Interior of a modern central evaporator
plant at Bainbridge, N.Y. Oil heat is used to evaporate
the sap in the four flue pans and high-pressure steam
is used at the finishing stage.

118

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

CENTRAL SAP EVAPORATOR PLANT

Chart 23. — Flow diagram: Oil-and-steani plant.

Coal is used in some areas, particularly
where it is cheap. It is best used to generate
high-pressure steam which, in turn, is used to
evaporate the sap (fig. 127).

As with oil-fired evaporators, a series of pans
is used. These pans, like the oil-fii-ed pans, are
mounted stepwise, as shown in figure 128. The
pans are heated with 80 to 110 p.s.i.g. steam in
coils or manifolds of ^/4-inch brass tubing
mounted at the bottom of the flat pans.

The specifications for a small plant (about
8,800 gal. per season) described by Pasto and
Taylor {86) are as follows:

Sap gallons per hour.

Water evaporated do

Sirup produced do

Tapholes number.,.

Fuel consumption gallons

Capital investment dollars. _.

Floorspace square feet

Sap storage gallons...

Density of

sap at —

1.6°

2.4°

Brix

807

815

792

14.7

22.2

32,000

23,800

25,291

1,226

20,000

Capital investment and cost for depreciation
and repairs for a small plant, as reported by
Pasto and Taylor {86), are given in table 18.

Smaller plants are in operation and are prov-
ing highly successful. Usually these plants are
small initially, but they are built so that they
can be enlarged after 2 or 3 years' operation.
Typical of these is the central evaporator plant
established in 1962 at Ogema, Wis. (fig. 124).
This plant has one 6- x 20-foot evaporator and a
separate finishing pan. Sap is supplied from
9,500 tapholes on 16 farms.

Operation

The sap supplied to the evaporator from the
storage tanks is fed to the first flue pan. Since
the flue pans are connected in series, the sap
flows successively through each pan to the
next. The sap is conducted between pans
through large-diameter, heat-resistant tubes or
pipe at least IV2 inches in diameter. The pans
can be installed in a stepwise manner to insure
no backward flow of sap from pans of higher
concentration to pans of lower concentration
and to better control the depth of the liquid
level in each pan. Since the elevation between
pans is only 6 to 8 inches, there is only a small
hydrostatic pressure in each interconnecting
feed line. Feed lines and valves must be large
enough to supply sap to the pans rapidly
enough under this low pressure to replace the
vast quantities of water being removed by
evaporation.

The liquid level in the evaporator pans is
maintained at a fixed depth by means of a
mechanical float valve or by an electrically
operated liquid level sensing element and sole-
noid valve. Whichever mechanism is used, it
must be sensitive to minute changes in liquid
level and must operate instantaneously. In
principle, when the finishing pan requires more
liquid to maintain its depth of sap, the sap is
obtained from the third pan of a 3-flue pan
installation, which in turn obtains more sap
from the second pan, and so on back to the
storage tank. The sirup is removed from the
finishing pan when it reaches standard density
(66.(f Brix) or slightly higher.

The operation can be automated by use of a
thermoswitch and solenoid valve. The thermo-
switch is adjusted to open the valve when the

MAPLE SIRUP PRODUCERS MANUAL

119

boiling sirup reaches the desired temperature
above that for boiling water at that location.
The operation is not completely automatic,
since the thermoswitch must be handset as

PN-)K23

Figure 127.— Where coal is inexpensive, high-pressure
steam boilers may be used to evaporate sap to sirup.

PN-4824

Figure i2^. — Interior of a multiple-pan, all-steam central
evaporator plant at Stoystown, Pa.

many as three or four times a day to compen-
sate for fluctuations in barometric pressure.
The U.S. Department of Agriculture has devel-
oped a new controller that will automatically
compensate for changes in the boiling point of
water due to changes in barometric pressure
(15).

In some installations, the partly concentrated
sirup is not supplied to the finishing pan by
gravity feed. Instead, an electric pump, acti-
vated by an electrically operated liquid level
sensing device in the finishing pan, removes the
sap from the last flue pan or semifinishing pan
when it reaches the desired concentration — any
point between 2(f and 60? Brbc.

If the Brix value of the sirup supplied to the
finishing pan is above 5(f , essentially all of the
sugar sand will have been formed and will be in
suspension. Its viscosity will be very low (see
table 13). It is advantageously filtered at this
point. The filtered sirup is then pumped into
the finishing pan. When it reaches the desired
density, it is automatically drawn by means of
solenoid valves and thermoswitch, and piped to
the holding or canning supply tank. With this
procedure, little or no sugar sand is formed in
the finishing pan. A cartridge-type filter can be
installed in this line to iwlish the sirup (that is,
remove the cloudlike precipitated sugar sand).
If the sirup is not prefiltered, it can be piped
from the finishing pan to a pressure filter such
as a plate-and-frame type and then to the
holding tank. Either method is desirable, since
once the sirup reaches standard density, it is
kept in a closed system so that it cannot evapo-
rate further.

To reduce holdup time, it is good practice to
keep the liquid level as low as possible in each
evaporator. There is, of course, always a danger
that because of some failure, insufficient liquid
will be fed to each pan and the pan will be
ruined by burning. This can be prevented by
connecting a hose to the raw-sap feed line by
which sap can be added quickly to any location
in any one of the pans.

Although a gas-fired finishing pan is satisfac-
tory for smaller plants, it is advisable to use
high-pressure steam for the finishing pan in
plants that make as much as 15 gallons of sirup
per hour. The steam permits finishing the sirup
without danger of burning it. The steam is best

120

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

supplied from an automatically operated, liijjh-
pressui-e boiler (80 to 110 p.s.i. and a rated horse-
I)ower of 20 or more).

If no prefilti'ation or inline cartridg:e filters
are used, the finished sirup can be efficiently
and economically filtered immediately after it is
drawn from the evaporator. A battery of three
or more open, flat, felt filtei's stsould be used.

Allowance must be made for loss of water as
steam while the sirup is being filtered. This loss
tends to raise the Brix value of the sirup
approximately Y .

S;i|> .S|||»|>|i4-|-s

Sap can be obtained in any one of three ways:
(1) It can be obtained from rented trees; (2) it

Table 18. — Capital investment in plant and equipment and cost of depreciation and repairs for

small oil-and-steam type plant '

Life
length

Yearly
depreciation

Yearly
repairs

Dollars

Land (1 acre at $200) 200.00

Roadway, ramps, grading

Building (1,226 sq. ft. at $4 per sq. ft.)

Equipment and other items:

Sap-receiving tanks (19,495 gal. at $0.08,3 per gal.)

Germicidal lamps for sap receiving tanks (12 at $25)

Pump for sap

Sap filter

Flue-type sap evaporators (4 at $650)

Arches for sap evaporators (4 at $287)

Covers and stacks for sap evaporators (4 at $160)

Steam semifinishing evaporator, size 5 x 6 ft

Cover and stack for semifinishing evaporator

Steam finishing evaporators and coils (2 at $100)

Hoods and stacks for finishing evaporators

Float valves (5 at $5)

Oil burners (4 at $332)

Smokestacks (4 base stacks at $31; 4 top stacks at $57)

Finishing filter (2 at $14.70) pressure cartridge

Finished sirup holding tank with heating device

Finshed sirup storage tank (3,940 gal. at $0.25 per gal.) __

Steam boiler (20 h.p.), installed

Oil tank (8,000 gal.)

Automatic sirup drawoff

Gravity filter

Pumps and motors to filter and to finishing evaporators (2

units at $75)

Can filling equipment

Thermometers (2 at $50)

Testing equipment ( re fracto meter, $100; hydrometer, $48;

scales, $150; thermometers, $10)

Portable power-stirring device

Water supply (well) plumbing, sink

Restroom furnishings

Office equipment

Other installation charges (burners, tanks, pumps, etc.,

besides cost of equipment)

Miscellaneous

Total

' About 8,800 gal. per year. 1962 dollars.
Source: Pasto and Taylor («6).

Dollars

500.00

22.50

15.00

4,904.00

147.12

1,618.08

72.81

48.54

300.00

27.00

9.00

150.00

13.50

4.50

50.00

4.50

1.50

2.600.00

189.00

63.00

1,148.00

103.32

34.44

640.00

57.60

19.20

138.00

12.42

4.14

108.00

9.72

3.24

200.00

18.00

6.00

100.00

9.00

3.00

25.00

2.25

.75

1,328.00

119.52

39.84

352.00

31.68

10.56

29.40

2.29

.76

75.00

6.75

2.25

985.00

44.32

29.55

4,485.00

201.83

134.55

1,000.00

45.00

30.00

100.00

9.00

3.00

140.00

12.60

4.20

150.00

13.50

4.50

50.00

4.50

1.50

100.00

9.00

3.00

308.00

27.72

9.24

300.00

27.00

9.00

1,000.00

45.00

30.00

500.00

15.00

500.00

45.00

15.00

912.00

82.08

27.36

800.00

72.00

24.00

25.791.48

1,502.,53

7.52.74

MAPLE SIRUP PRODUCERS MANUAL

121

can be picked up at the farm; or (3) it can be
delivered to the plant (figs. 129 and 130).

The quality of sap is not easy to judge by
visual inspection. But the buyer must guard
against purchasing spoiled or unsound sap,
since a small amount could contaminate a large
amount of sound sap when added to it. The
plant operator must therefore exercise some
control over the production of sap by the sap
suppliers. He therefore should set certain mini-
mum standards.

I'rotliirtioii Stdmlards for Sa/t I'.ollevted in
Buckets

(1) All buckets must be covered.

(2) Buckets must be clean and sanitized be-
fore use.

(3) In midseason or after a warm period,
buckets must be washed again.

(4) Collecting buckets and tanks must be kept
clean and sanitized.

(5) Sap (even a very small amount) that has
remained in buckets between runs must be
discarded.

Production Standards for Sfip Collected in
Plastic Tubinfi

(1) Only clean tubing must be installed.

(2) All collecting or venting equipment must
be washed and sanitized.

Standards for Slorti^e Tanks on Sti/t harms

(1) All tanks must be washed and sanitized
before the start of the sap season.

(2) Tanks must be completely emptied,
washed, and sanitized at least twice each sea-
son and preferably between each run of sap.

PN-ia2.s
Figure 129. — Sap i.'i delivered to a central evaporator
plant in a variety of vehicles. These vehicles are waiting;
to unload.

PN-4826

Figure 130. — Sap is delivered in all types of containers
(including- milk cans) and by eveiy available type of
conveyance ranging from the trunks of passenger cars
to trailers drawn by farm tractors.

Pi-oduction of a darker grade of sirup indicates
that the tank needs washing and sanitizing.

(3) Tanks should be covered with clear, trans-
parent plastic that transmits the sanitizing
ultraviolet radiation of sunlight.

(4) Tanks must be constructed with smooth,
easily cleaned surfaces.

Metal tanks best meet the requirements.

l*iirohafi«' of Sap

Sap is bought on the basis of the total weight
of solids (sugar) it contains. It is necessary to
measure with precision the volume of the sap to
the nearest gallon, its density to the nearest
0.1° Brix, and its temperature to the nearest ° F.

The volume of sap can be determined in
several ways, as follows:

(1) By means of a meter through which the
sap can be pumped or can flow by gravity. This
is the most precise and direct method, provided
the meter is calibrated carefully and is checked
frequently. Be sure the meter is designed for
operation at low pressures.

122

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

(2) By use of tanks of standard sizes cali-
brated in gallons for different depths of liquid.
The calibrations are usually made on a "dip
stick" calibrated for a specific tank size. The
stick is lowered vertically to the bottom of the
tank and the heipfht of the sap in the tank is
noted by the wet line on the stick. This line
indicates the depth and volurne of the sap.
Usually, when sap is delivered to the plant, it is
run into a receiving tank that can be calibrated
precisely. The calibrations should be accurate
to ± 1 gallon.

(3) By its weight. The tank of sap is weighed
before and after emptying. The empty (tare)
weight is subtracted from the weight of the
tank and sap to obtain the weight of sap. The
weight of sap is divided by 8.39 (the weight of 1
gallon of sap).

The only tangible constituent of sap that can
be used to establish its price is its solids con-
tent, which is measured and expressed as
° Brix. This measurement is made at the plant
by using a quart sample taken when the sap
was picked up at the farm or when it was
delivered to the central plant (fig. 131). The
sample identified with supplier's name and date
can be stored a few hours before determining
its Brix value. Or its Brix value can be deter-
mined at the time the sap is picked up or
delivered provided its temperature is also deter-
mined at that time.

The observed Brix value of the sap is the
value read to the nearest 0.1° from the test
instrument (hydrometer or refractometer); this
value, together with the measured temperature
of the sap, is recorded. From these, the true
Brix value of the sap is calculated.

Corrections to be applied to the observed Brix
value to obtain the true Brix value of saps of
various temperatures are as follows:

Temperature of sap, ° F.

32-42

43-53

54-62

63-66

Correction to subtract from
observed Brix value

CBrix)

0.4

The value of sap is not constant but varies
with its solids content (percentage of sugar), or
Brix value. The higher the Brix value, the
smaller the amount of sap required to produce

1 gallon of sirup. Less water has to be evapo-
rated, less volume is handled, and less storage
space is required. Sap with the highest Brix
reading therefore has the highest value.

The base price for sap is usually for sap of 2"
Brix. This base price is determined by a num-
ber of factors, the most important of which is
the price of the finished sirup. For sirup selling
at $9 to $12 a gallon, one New York producer
reported in the National Maple Syi-up Digest (1)
the following prices paid for sap delivered at
the evaporator plant in 1974. The prices can be
adjusted up or down by such factors as effi-
ciency of the plant, hours of operation, and
wage scales.

True Brix value of sap '

1.5°
1.6°
1.7°
1.8°
1.9°
2.0°
2.1°
2.2°
2.3°
2.4°
2.5°
2.6°
2.7°
2.8°
2.9°
3.0°
3.1°
3.2°
3.3°
3.4°
3.5°
3.6°

3.r

3.8°
3.9°

4.0°

Price per gallon
(cents)

2.9

3.9

4.9

5.8

6.6

7.3

7.9

8.5

9.1

9.7

10.2

10.7

11.2

11.7

12.2

12.7

13.2

13.7

14.2

14.7

15.2

15.7

16.2

16.7

17.2

17.7

' True Brix value is the observed Brix reading corrected
for temperature.

Storing Sap

The central evaporator plant must provide
facilities to store a full day's production of sap.
There is no precise means for estimating the
size. However, experience has shown that on
days when sap flows well, ft'om 4,000 to 20,000
gallons will be produced per 10,000 tapholes.
Thus, a plant having a capacity of 8,800 gallons

MAPLE SIRUP PRODUCERS MANUAL

123

PN-4827

Figure 131. — A sample of sap is taken for determining its
Brix value and for judging its quality. The observed
Brix value, temperature, and volume of the sap are
recorded for each delivery.

of sirup annually would I'equire sap from 10,000
to 35,000 tapholes, or 70,000 gallons of sap per
day. Since the plant would be operating contin-
uously after the first delivery of sap, the re-
quired storage facilities would be somewhat
less than the daily requirement of sap.

Storage tanks can be made of several mate-
rials and in several shapes. Metal-lined tanks
are preferred because their surfaces are
smooth, easily cleaned, and sanitary. Concrete
tanks are the most difficult to keep clean be-
cause droplets of sap, in which micro-organisms
can gi'ow, can lodge in the rough surfaces.
Concrete walls can be made smooth with differ-
ent types of coatings; however, before the walls
are coated, clearance for the use of the particu-
lar coating should be obtained from State and
Federal food agencies. Plastic tank liners also
have been used successfully, especially in
wooden tanks.

The storage tanks should be located in a cool
place. Aboveground storage is preferable be-
cause of ease in making repairs and cleaning.
All tanks must be covered- If the tanks are not
equipped with germicidal lamps, they should
have transparent plastic covers and should be
located to receive as much sunlight as |X)ssible.

Because of the depth of the sap in the tanks,
the efficiency of daylight sterilization is low. It
is recommended that germicidal lamps be used.
One or more lamps should be arranged to illu-
minate the entire surface of the sap. The lamp
fixture should be provided with a bright metal
reflector so that most of the ultraviolet radia-
tion will be used. These lamps are also effective
in sanitizing empty or partly empty tanks, pro-
vided no buildup of foam or solids has occurred
on the tank walls.

CAUTION

(!aro nmst

(■x<'r<'is«M

not to

.■X

>OM-

tlio <

vcs lo

•Uro

<•! iiltra\iolc

1 ra<

lial

ion.

.4lHa\

•> turn

he 1

amps olT

vth<

•11 th

■ 1;

inks

ai-e <•

t-aiicd or \^

lien ihcv

art'

opciic*

lor

»'iil<'i

iii^ <>r

for

iiis|M-cli<>ii.

riti

a\ioh-t 1

rays.

<-an «!<>

irr<

parahlr

(hiiiiag)'

Ih.-

evt's.

The receiving tank (fig. 132) should be placed
alongside a ramp so that the sap in the hauling
tanks can be emptied into it by gravity. In some
localities it is possible to have the receiving
tanks installed higher than the storage tanks
so that they also can be filled by gravity.

Figure 132. — The sap is filtered as it
receiving tank.

PN-4828

is run into the

124

AGRICULTURE HANDBOOK 184, U.S. DEPT. OF AGRICULTURE

However, the more common method is to move
sap from the receiving: tanks to the storage
tanks by i)iimi)s.

Sap obtained from pijDelines is usually free of
foreign matter and does not need to be filtered.
However, sap obtained by other collecting
methods must be filtered to remove fine parti-
cles of bark and other foreign matter from the
sap. If not removed, this foreign matter may
serve as an unwanted source of color and cause
the production of dark, low-gi-ade sirup.- The
filter may be either a presscloth prefilter or
several thicknesses of muslin (fig. 133).

It is desirable to use two or more sap-storage
tanks. This permits better control of sanitation,
plant operation, and production records. The
Brix value of the sap in each tank must be
determined since it may be a composite of sap
obtained from two or more sources that may be
of different sugar contents. If the volume of sap
in the tank and its Brix value are known, the
yield of finished sirup can be calculated (see p.
48).

The evaporator house must be provided with
a gage to show the volume of sap in the storage
tank being used to supply sap to the evapora-
tor. Without a gage, the plant operator may
unexpectedly find the supply of sap exhausted,
and the evaporator pans may go diy and be
damaged by bm-ning. A simple type of gage can
be installed in the sap feed line from the tank to

PN-1H29

Figure 133. — Several layers of muslin or presscloth can be
used to filter sap.

the evaporator This gage consists of a tee with
a long, upright, glass sight tube, the top of
which is open and above the level of the top of
the storage tank. The level of the sap in the
tube indicates its depth in the storage tank.
The tube can be calibrated in units such as full,
'/.,-full, etc., or in gallons.

Handling und Storing Sirup

Sirup tends to become darker each time it is
heated above 18(F F. Therefore, sirup should be
reheated as few times as possible. To insure a
sterile package, all sirup must be packaged at
temperatures above 19(F. It is advisable to
package the sirup immediately after it leaves
the filter or the finishing pan while it is still
above 190^. If the temperature of the sirup
drops below 19(]F before it can be packaged, a
small amount of heat furnished by a steam coil
with high-pressure steam, an electric immer-
sion heater, or a heat lamp will bring it back to
the desired 19(7 with a minimum of darkening.

Sirup not immediately packaged can be put
in bulk storage. If it is stored in drums, they
must be completely filled with hot sirup
(19(F F.). Large tanks holding several hundred
or several thousand gallons can be used. Sirup
storage tanks, like sap storage tanks, should be
provided with germicidal lamps mounted to
illuminate the entire surface of the sirup when
the tank is filled. These lamps must be kept in
operation continuously from the time the tanks
are cleaned prior to filling until the last of the
stored sirup has been removed. If the sirup is
run into these tanks hot and sterile, there is
little chance that any microbial gi'owth will
occur below the sirup surface, and the germici-
dal lamps will keep the surface sterile. Sirup
stored in this way can be held indefinitely and
sirup can be added or withdrawn at any time. It
is not necessary to keep the tank cool. Tanks
with sterile lamps can be mounted outside, for
the ambient temperature has little or no effect
on keeping quality of the sirup. The sirup with-
drawn for packaging must be heated to sirup-
pasteurizing temperature (190" F.).

The large storage tank also serves as a set-
tling tank. After several weeks of storage, the
sirup will be sparkling clear.

MAPLE SIRUP PRODUCERS MANUAL 125

SailitUtioil ^- Labor (supervisor plus hourly wages at

$1.50 per hour) 1,255

The central evaporatinfj plant is a fond proc-

essing: plant. It must be maintained in the same Total '

clean and sanitary manner that is required of . „ ^ . , ,

..„,." F. Income (8,800 gallons of sirup produced;

all food plants. price received per gallon, $4.3,'ir 38.104

The evaporator room and any other rooms m Net profit, F - (B + c+D + E), or $38,i04 -

the plant should be kept free of steam. Moist $28,211 9,893

surfaces are sites for microbial growth. Steam Return on capital investment:

is easily removed from the evaporators by us- ^ jqq ^ ^g percent "

ing the closed venting system described on page $25,291
40.

The floors should be constructed of smooth ' Except for average price per gallon of sirup, these

. r 1 • data are adapted from Pasto and Taylor (86).

masonry for ease of cleaning. , g^^ ^^^1^ jg j.^^ itemized capital expenditure.

The sirup should be packaged in a separate :< p^^ed costs, with the possible exception of salaries

room or area that can be kept clean and free of paid to management, remain constant irrespective of

dust. Clean all equipment at frequent intervals. production.

When detergents and scale-removing chemicals ] Cost of sap. This depends on two variables: (i) The

, . , , i 1 J u volume of sap processed, and (2) the Brix (percent oi

are used, they must be completely removed by ^^,g^^, ^^ ^^^ ^^p ^^^^ ^^^ ^^^^ ^^^^^^ p^^^ p^i^ f^,. ^^p

at least three successive rinses with clean, clear ^f 2.4° Brix in 1963.

water. ' The price received for a gallon of sirup is based on an

Only clean utensils should be used and in- assumption that '/:, will be sold in bulk at $3 per gallon, 'A,

Struments should be kept free of sugar sand. at a bulk price of $4, and V., sold retail at $6 per gallon.

Return on capital for sirup at the plant; does not
include marketing costs.

Economics

^, , , , • ■ -1 r The previous data assume maximum produc-

The central evaporator plant is primarily tor . ,. n i ^ t ^ t-- i^

^ . , r. r, ■ I tion tor a small plant. Less production would

concentrating sap to sirup and tor iiltering and , <.<■•* j • e ■ <- ^

r „ , ^ XI • -^ -11 u reduce net profit and income from invested

packaging sirup. When used tor this, it will be . ,

operated only 6 to 8 weeks a year. Yet even
with this short period of use, Pasto and Taylor

(86) found in 1962 that such a plant could pay Material lialaun'

an excellent return on the invested capital. The Seldom will the actual amount of sirup pro-
following calculations, based on Pasto and Tay- duced equal that calculated from the amount of
lor's data, show how profitable such an opera- gap purchased and the Brix value of the sap.
tion could have been at that time. By recalcu- Pasto and Taylor (86) suggested that there is a
lating, using current costs and prices, one could 2-percent loss in sirup. They suggested that this
determine whether the return to be expected is due to sirup left sticking to the walls of the
would be higher or lower than that shown here. evaporators, holding tanks, and felt filters. This

apparent loss is caused (1) by making sirup that

Returns on capitalinvestment in small central evaporator is too heavy (a Brix value above 66.(f), and

plant used only for processing sap and filtering and selling this heavy sirup on a volume basis

packaging sirup ' rather than on a weight basis; (2) by overfilling

. , X i , . . . . cSc Of,, sirup containers; as little as 5-percent overfill in

A. Investment in plant and equipment ■ $25,291 •, , , ■ ,

the retail package results in only 950 gallons oi

Costs (operating): sirup for each LOGO gallons handled — a loss of

B. Fixed (management, interest on borrowed 50 gallons; and (3) by removing during filtration

capital, depreciation, repairs, insurance, sugar sand that was measured in sap as sugar.

property taxes)' 6,277 ^p^^ longer the plant is in productive opera-

Variable: "

C. Sap supplies (322,292 gal. (2.4° Brix) at tion (hours and days) and the greater the vol-

$0,052 per gal.)^ 16,7.59 ume of sirup produced, the greater will be the

D. Fuel (26,136 gal. oil at $0.15) 3,920 profits and returns on the investment.

126

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

I iH-rcasinf! Returns

Use of central plant facilities need not be
limited to the 6 or 8 weeks of sap evafwration.
Instead, the facilities can be put to a number of
other uses that not only produce more income
from the invested capital but also furnish prof-
itable employment.

Additional uses for the plant~are: (1) Mixing
of sirups to obtain a standard grade and den-
sity; (2) custom packaging of sirup; (3) prepar-
ing gift packages; (4) reprocessing sirup to re-
move buddy flavor; (5) making high-flavor sir-
up; (6) preparing high-density sirup; and (7)
manufacturing confections.

Some additional equipment would be re-
quired. This includes a steam kettle for use in
processing sirup and in manufacturing confec-
tions and a candy machine and facilities for
manufacturing confections.

Standardizing Sirup for Color
and Density

Today, the consumer exjjects uniformity in
food products. The public, therefore, expects
uniformity (year after year) in the color (gi-ade)
and density of maple sirup. The color and den-
sity can easily be adjusted to meet specific
customer demands by mixing sirup of different
grades and different densities. This must be
done after the sirupmaking season so that the
amount of different sirup stocks will be known.

Adjiisliiif: Color

To adjust the color, measure 1 cup of either
the lighter sirup or the darker sirup in a 2-cup
measurer. Then add the other with constant
mixing until the desired color (grade) is
reached. Note the amount of sirup added in
ounces. This will give the ratio of the light and
dark sirups to be mixed to produce the desired
grade.

Stirring sirup in .5-gallon tins makes it easier
to select different gi-ades for mixing.

Adjiisling Ih'iisilY

To adjust the density, preferably to between
66^ and 67° Brix, the method of Pearson's
Square can be used. Considerable time can be
saved by calculating the number of parts (by
weight) of the heavy sirup to mix with sap or
thin sirup to obtain standard-density sirup.

Example 1. If a dense sirup of 70^ Brix is to be
mixed with a thin sirup of 64.4' Brix to make a
standard-density sirup of 66.0^ Brix, the quan-
tity of each sirup to be used can be determined
by alligation as follows:

A = 70

D = 1.6 (calculated)

C = 66.0

B = 64.4

4.0 (calculated)

where A = density of heavy sirup in ° Brix
B = density of light sirup in ° Brix
C = density desired as the result of mix-
ing A and B

This is always the center figure. D = the
difference between C and B, which in this case
= 1.6. E = the difference between A and C,
which in this case = 4.0. D and E give the ratios
of sirup A and B to mix to produce standard-
density sirup (66.0P Brix), which in this case
would be 1.6 parts of A (heavy sirup) to 4.0
parts of B (light sirup).

Example 2. If sirup with a density of 66.5^
Brix is desired (it will feel better to the tongue)
using the same two sirups, the Pearson Square
would become

D = 2.1

C = 66.5

B = 64.4

E = 3.5

The ratio of these two sirups mixed to give a
sirup having a density of 66.5" Brix (C) would be
2.1 parts of A (hea\y sirup) to 3.5 parts of B

(light sirup).

rii<<loiii l'a<-kafiiiiji and (.ill l'a«'ka}>;«'.s

Many customers want sirup packaged in con-
tainers of special design and shape. This re-
quires special handling, and is usually done
after the. sap season.

MAPLE SIRUP PRODUCERS MANUAL

127

Many companies and some individuals are
using gift packages for a selected clientele.
These gift packages consist of a variety of
maple products attractively packaged. Orders
are usually received and made up for special
occasions, particularly for the Christmas sea-
son.

Ili{>;h-Klav<n<'<l ami Hish-Densitv Sirup

To meet ever-increasing demands for high-
flavored sirup (described on p. 106) for use in
making some maple-blended table sirups, a con-
siderable portion of bulk sirup will require high
flavoring. Most of this will be done by the open
steam-kettle process or by the new continuous
process.

High-density sirup will also need to be made
to meet consumer demands. The process is
described on page 105.

Man iiliK'l lire «(' (',<»iirec>tions

All well-managed central evaporator plants
should have a candy kitchen for manufacturing
confections (fig-s. 134-136). The cost of convert-
ing standard-density sirup to confections is
small compared to the selling price of the con-
fections; confection manufacture is the most
profitable enterprise of the central plant. The
principal confections made are maple cream,

PN-4k:!U

Figure 13i. — A well-equipped candy kitchen with dehu-
midifier and air-conditioner is an essential part of a
central evaporator plant. The candy kitchen furnishes
employment a major part of the year.

PN-1831

Figure 135.— A central evaporator plant must have a
salesroom for displaying- and selling the products
manufactured.

PN^832

Figure 136.— A large, easily read sign advertising the
central evaporator plant is essential for directing the
public to the plant for the purchase of maple products.

maple candies (soft sugar), block sugar, and
stirred sugar.

The candy kitchen of the central plant will be
in operation from 9 to 12 months of the year.
The manufacture of confections may use more
than half the plant's sirup production and will
provide the largest source of income per gallon
of sirup. A small central evaporator plant may
produce more than 4 tons of confections a year.

128

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

.Siiniiiiar>

(1) Theoi-etically, the central evai)orator plant
is sound economically for both the plant
investor and the suppliers of sap.

(2) Locate it on an accessible, hard-surfaced,
touri.st-traveled road.

{'.i) The plant need not be larp:e, but the larger
the plant, the larger the returns. Central
evaporator plants are readily expanded.

(4) The most common plant is one using oil
fuel for the bulk of the sap evaporation
and high-pressure steam for the last stage
of the evaporation.

(5) Utilize automation where jwssible.

(6) Sap should be purchased on the basis of its
Brix value and volume or weight. The
price of sap should be on a sliding scale,
vai-ying with the " Brix of the sap.

(7) Standards of production should be set for
sap producers.

(8) Sap storage facilities must be adequate to
handle a maximum day's run from all of
the sap suppliers.

(9) Sap tanks should be located in a cool place,
easily accessible for washing and sanitiz-
ing. Tanks should be provided with germi-
cidal lamps to prevent sap deterioration by
microbial s{X)ilage.

(10) Bulk storage of sirup can be in large tanks
protected by germicidal lamps or in 5-gal-
lon tins or 30-gallon drums.

(11) Sirup for retail trade should be mixed to
obtain a standard color and density and
packaged at 190P F.

(12) Increased returns from the plant will re-
sult from extending its use throughout the
year by manufacturing confections, cus-
tom-packaging sirup, and preparing gift
packages of assorted maple products.

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130

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132

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1954. VALSA LEUCOSTOMOIDES, THE CAUSE OF
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SUGAR MAPLES. Phytopathology 44: 12-13,
illus.

(110) STEVENSON, D. D., and BaRTOO. R. A.

1940. COMPARISON OF THE SUGAR PER CENT OF
SAP IN MAPLE TREES GROWING IN OPEN AND
DENSE GROVES. Pa. State Forest Sch. Res.
Paper 1, 3 pp. [Processed.!

(111) Strolle, E.g., Cording, J., Jr., and Eskew, R. K.

1956. AN ANALYSIS OF THE OPEN-E'AN MAPLE-
SIRUP EVAPORATOR. U.S. Agr. Res. Serv.
ARS 73-14, 14 pp., illus.

(112) TAYLOR, F. H.

1956. VARIATION IN SUGAR CONTENT OF MAPLE
SAP. Vt. Agr. Expt. Sta. Bui. 587, 39 pp.

(113) Trenk, F. B., and McNall, P. E.

1954. COSTS OF PRODUCING MAPLE SYRUP IN Wl.s-
CONSIN. IWis. Agr. Expt. Sta.! 6 pp., il-
lus. [ Processed. 1

(114) TRESSLER, C. J., and ZIMMERMAN, W. 1.

1942. THREE YEARS' OPERATION OF AN EXPERI-
MENTAL SUGAR BUSH. N.Y. State (Geneva)
Agr. Expt. Sta. Bui. 699, 24 i)p.. illus.

(115)

(116)

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Underwood, J. C.

1963. QUICK TEST FOR "BUDDY" FLAVOR IN MAPLE
SIRUP. U.S. Agr. Res. Serv. ARS 7.3-12, 4 pp.

EFFECT OF HEAT ON THE FLAVORING COM-
PONENTS OF MAPLE SIRUP: A PRELIMINARY
STUDY BY GAS CHROMATOGRAPHY. Jour.
Food Sci. 36: 228-230.

and FlUPIC, V. J.

GAS CHROMATOGRAPHIC IDENTIFICATION OF
COMF'ONENTS IN MAPLE SIRUP FLAVOR EX-
TRACT. Assoc. Off. Agr. Chem. Jour. 46:
334-337.

(118)

(119)

(120)

(121)

(122)

(123)

(124)

(125)

(126)

(127)

and LENTO, H. G.

1960. SOME PHYSICAL CHARACTERISTICS OF THE
2,4-DINITROPHENYLHYDRAZINE AND SEMI-
CARBAZIDE DERIVATIVES OF THREE-CARBON
CARBONYLS. Anal. Chem. 32: 1656-1658.

LENTO, H. G., Jr., and WiLLITS, C. O.

1956. TRIOSE COMPOUNDS IN MAPLE SIRUP. Food

Res. 21: 589-597.
Lento, H. G., Jr., and Willits, C. O.

1959. BROWNING OF SUGAR SOLUTIONS. 3. EF-
FECT OF PH ON THE COLOR PRODUCED IN
DILUTE GLUCOSE SOLUTIONS CONTAINING
AMINO ACIDS WITH THE AMINO GROUP IN
DIFFERENT POSITIONS IN THE MOLECULE.
Food Res. 24: 181-184.

and WILUTS, C. O.

1959. SCALE IN MAPLE-SIRUP EVAPORATORS-
HOW TO REMOVE IT. U.S. Dept. Agr. Inform.
Bui. 203, 4 pp.

Willits, C. O., and Lento, H. G.

1961. BROWNING OF SUGAR SOLUTIONS. VI. ISO-
LATION AND CHARACTERIZATION OF THE
BROWN PIGMENT IN MAPLE SIRUP. Jour.
Food Sci. 26: 397-400.

WILUTS, C. O., and LENTO, H. G.

1961. MAPLE SIRUP. XVI. ISOLATION AND IDEN-
TIFICATION OF COMPOUNDS CONTRIBUTING
TO THE FLAVOR OF MAPLE SIRUP. Jour.
Food Sci. 26: 288-290.

United States Department of Agriculture.

1949. trees; the yearbook of agriculture,

1949. 944 pp., illus. Washington, (Various
references to maple sugar.)

1952. AGRICULTURAL STATISTICS 19!-.2. 876 pp.
Washington.

1956. AGRICULTURAL STATISTICS ig.'io. 610 pp.
Washington.

1963. AGRICULTURAL STATISTICS 19fi2. 741 pp.
Washington.

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1972. AGRICULTURAL STATISTICS 197
Washington.

759 pp.

MAPLE SIRUP PRODUCERS MANUAL

133

(129) United States Department of Agriculture,

Consumer and Marketing Service.
1967. united states standards for grades of

TABLE MAPLE SIRUP. (Effective May 24,
1967). 2 pp. (Processed.!

(130) UNITED States Food and Drug Administra-

tion.
1962. FOOD additives. Fed. Register 27: 1554.

(130a)

1974. FOOD LABEUNG. Fed. Register 39: 20882.

(131) Vermont Department of Agriculture.

1950. vermont maple syrup grading and
marketing law, effective march 1,
ig.'iO. Vt. Dept. Agr., Div. Mkts. Cir. 14, 16
pp.

(132) Vermont Development Department and Ver-

mont Department of Agriculture.

1962. VERMONT maple sirup and SUGAR. 16 pp.,
illus. Montpelier, Vt. (Rev.)

(133) Wasserman, a. E.

1963. microbiology and sanitation in the
sugar bush and sugar house. u.s. agr.
Res. Serv. ARS 73-41, 18 pp., illus.

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1964.

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1962.

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1961.

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MAPLE SIRUP. XXII. CONTROLLED FER-
MENTATION OF BUDDY MAPLE SIRUP. Food
Techno!. 18: 142-145.
UNDERWOOD, J. C, and WiLUTS, C. O.

FLUFFED MAPLE PRODUCTS — A NEW USE
FOR MAPLE SIRUP. U.S. Agr. Res. Serv.
ARS 73-39, 6 pp.
and WILLITS, C. O.

MAPLE SIRUP. XX. CONVERSION OF
"BUDDY" MAPLE SAP INTO NORMAL MAPLE
SIRUP. Food Technol. 15: 438-439.
- and WILLITS, C. O.
In. d.l PREPARATION OF MAPLE SIRUP FROM

BUDDY SAP. Filed in Patent Office 10/17/61

as Serial No. 145,783. (Pat. pending.)

(138) WEBER, P. D.

1956. WISCONSIN MAPLE PRODUCTS; PRODUCTION
AND MARKETING. Wis. Dept. Agr. Bui. 335,
48 pp., illus.

(139) Whitby, G. S.

1936. manufacture of maple products of in-
TENSE FLAVOR. (U.S. Patent No.
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(140) WiLUTS, C. 0.

1951. CROPS FROM THE MAPLE TREES. U.S. Dept.
Agr. Ybk. Separate 2208. [Reprint from
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321.)

(141)

(142)

1953. SOME CHANGES THAT SAP UNDERGOES IN A
CONTINUOUS ATMOSPHERIC EVAPORATOR.
Second Conf. on Maple Prod. (U.S. Agr. Res.
Serv., East. Util. Re.s. Br., Philadelphia, Nov.
16-18). Rpt. Proc. 2: 30-32. [Processed.]

MAPLE AIDS IN BETTER LAND USE PRO-
GRAM. Natl. Maple Syrup Digest 1 (3): 8, 10.

(143)

1962. MODERNIZATION OF THE MAPLE SYRUP IN-
DUSTRY. Natl. Maple Syrup Digest 1 (1): 6-
7.

(144) Frank, H. A., and Bell, R. A.

1959. CLEANING PLASTIC EQUIPMENT USED IN
HANDLING MAPLE SAP. U.S. Agr. Res. Serv.
ARS 73-23, 12 pp.

(145) Frank, H. a., and Underwood, J. C.

1960. MAKING HIGH-DENSITY, HIGH-FLAVORED
MAPLE SIRUP. U.S. Agr. Res. Serv. ARS 73-
26, 8 pp.

(146) Frank, H. A., and Underwood, J. C.

1960. MEASURING THE SUGAR IN MAPLE SAP AND
SIRUP. U.S. Agr. Res. Serv. ARS 73-28, 21
pp.

(147) Frank, H. A., and Underwood, J. C.

1961. filtration of maple SIRUP. Jour. For-
esti-y 59: 112-113.

(148) and PORTER, W. L.

1950. MAPLE SIRUP. II. A NEW HIGH-FLAVORED
MAPLE SIRUP. U.S. Bur, Agr. and Indus.
Cheni. AIC-269, 3 pp.

(149) and PORTER, W. L.

1955. PRODUCTION OF MAPLE SUGAR PRODUCTS
HAVING ENHANCED FLAVOR. (U.S. Patent
No. 2,715,581.)

(150) Porter, W. L., and Buch, M. L.

1952. MAPLE SIRUP. V. FORMATION OF COLOR
DURING EVAPORATION OF MAPLE SAP TO
SIRUP. Food Res. 17: 482-186, illus.

(151) SHOLETTE, W. p., and UNDERWOOD, J. C.

1958. THE DETERMINATION OF MALIC ACID IN MA-
PLE SIRUP BY AN ION EXCHANGE PROCE-
DURE: AN ADAPTATION OF THE GOODBAN
AND STARK METHOD. Assoc. Off. Agr. Chem.
Jour. 41: 658-662.

'152) and SiPPLE, L.

1961. THE USE OF PLASTIC TUBING FOR COLLECT-
ING AND TRANSPORTING MAPLE SAP. U.S.
Agr. Res. Serv. ARS 73-35, 19 pp., illus.

(153) and UNDERWOOD, J. C.

1961. METHODS OF ANALYSIS FOR MAPLE SIRUP:
USDA COLOR COMPARATOR. Assoc. Off Agr.
Chem. Jour. 44: 330-333.

(154) Underwood, J. C, and Lento, H. G.

1959. PROCESS FOR MAKING MAPLE PRODUCT OF
INTENSIFIED MAPLE FLAVOR. (U.S. Patent
No. 2,895,833.)

(155) Underwood, J. C, Lento, H. G., Jr., and

RICCIUTI, C.
1958. browning of SUGAR SOLUTIONS. I. EF-
FECT OF PH AND TYPE OF AMINO ACID IN
DILUTE SUGAR SOLUTIONS. Food Res. 23:
61-67.
(1.56) Winch, F. E., Jr.

in. d.l bacterial control for higher quality

SAP. Inform. Sheet.
(157) and MORROW, R. R.

1962. PRODUCTION OF MAPLE SIRUP AND OTHER
MAPLE PRODUCTS. N.Y. (Cornell) Agr. Ext.
Bui. 974, 40 pp. (Rev.)

134

AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE

SUPPLEMENTAL READING

Anonymous.

1940. maple sugar [sirup] in cigarettes. can-
ada Lumberman 60 (8): 12.

1942. CANADIAN MAPLE HARVEST. Jour. Forestry
40: 806. _

ANDERSON, W. R., and METEER, J. W.

1948. MAKING FARM FORESTRY PAY. Ohio Forestry
Assoc. News Bui. 1 (2): 111-2.

ASHE, W. W.

1897. THE POSSIBIUTIES OF A MAPLE SUGAR INDUS-
TRY IN WESTERN NORTH CAROLINA. N.C.
Geol. Survey, Econ. Papers 1, 34 pp., illus.
BARRACLOUGH, K. E.

1952. MAPLE SYRUP AND SUGAR PRODUCTION IN
NEW HAMPSHIRE. N.H. Univ. [Agr.) Ext. Bui.
103. 28 pp., illus.
BATES, F. J., and BeARCE, H. W.

1918. NEW BAUM6 SCALE FOR SUGAR SOLUTIONS.
[U.S.] Natl. Bur. Standards Technol. Papers
115, 11 pp.
BERKSHIRE Pioneer Maple Producers' Association.

In. d.l MASSACHUSETTS PURE MAPLE SYRUP. 7 pp.
Ashfield, Mass.
Bryan, A. H.

1910. MAPLE-SAP SIRUP: ITS MANUFACTURE, COM-
POSITION, AND EFFECT OF ENVIRONMENT
THEREON. U.S. Bur. Chem. Bui. 134, 110 pp,
illus.
Hubbard, W. F., and Sherwood, s. F.

[1923.1 PRODUCTION OF MAPLE SIRUP AND SUGAR.
U.S. Dept. Agr. Farmers' Bui. 1366, 35 pp.,
illus. (Rev. 1937.)

StraUGN, M. N., Church, C. G., and others.

1917. MAPLE SUGAR: COMPOSITION, METHODS OF
ANALYSIS, EFFECT OF ENVIRONMENT. U.S.
Dept. Agr. Bui. 466, 46 pp., illus.
CHITTENDEN, A. K., and ROBBINS, P. W.

1930. THE COST OF MAKING MAPLE SYRUP. In The
Farm Woodlot in Michigan, Mich. Agr. Expt.
Sta. Spec. Bui. 196, p. 14.
CHRISTOWE, M.

1946. GREEN MOUNTAIN SAP. Farm Quart. 1 (4): 38-
43, 134-1.35, illus.
COLLINGWOOD, G. H., and COPE, J. A.

1938. MAPLE SUGAR AND SIRUP. N.Y. Agr. Col. (Cor-
nell) Ext. Bui. 397, .32 pp., illus. (Rev. 1944.)
Cope. J. A.

1949. DEPTH OF TAPPING IN RELATION TO YIELD OF
MAPLE SAP. Jour. Forestry 47: 478-480.

1949. MAPLE SIRUP AND SUGAR. N.Y. Agr. Col. (Cor-
nell) Ext. Bui. 397, .32 pp., illus. (Rev.) [First
printed 1938; the revision reprinted 1952.1
Dambach, C. a.

1944. comparative productiveness of adjacent
grazed and ungrazed sugar-maple
WOODS. Jour. Forestry 42: 164-168. illus.

Dansereau, p.

1944. L'INDUSTRIE DE L'ERABLE. Universite de
Montreal, Institut de Biologie (Secretariat de
la Province de Quebec, Service de Biogeogra-
phie). 44 pp., illus. [Quebec. I [Processed.]
Edson, H. a., Jones, C. H., and Carpenter, C. W.

1912. MICRO-ORGANISMS OF MAPLE SAP. Vt. Agr.
Expt. Sta. Bui. 167: [3211-610, illus.
Fabian, F. W., and Buskirk, H. H.

1935. AEROBACTER AEROGENES AS A CAUSE OF
ROPINESS IN MAPLE SIRUP. Indus, and Engin.
Chem., Indus. Ed., 27: .349-450.
Finlay, M. C.

11934.] our american maples and some others.
19 pp., illus. New York.

GILMAN, W.

1949. MAPLE— THE MYSTERY TREE.
42: 119-122, illus.
GOING, M.

1917.

Nature Mag.

Canad. For-

IN THE MAPLE SUGAR SEASON.

estry Jour. 13: 992-994, illus.
GROSE, L. R.

1920. MAPLE SUGAR IN COLONIAL TIMES. Amer.

Forests 26: 689-690.
Hayward, F. W.

1946. THE STORAGE OF MAPLE SIRUP. N.Y. State
Agr. Expt. sta. Bui. 719, 8 pp., illus.

and PedeRSON, C. S.

1946. SOME FACTORS CAUSING DARK-COLORED MA-
PLE SIRUP. N.Y. State Agr. Expt. Sta. Bui.
718, 14 pp.. illus.
Herbert, P. A.

1924. the weather and MAPLE SUGAR PRODUC-
TION. Mich. Agr. Expt. Sta. Quart. Bui. 7: 60-
62, illus.
Herr, C. S.

1938. maple syrup and sugar production in
NEW HAMPSraRE. N.H. Univ. lAgr.l Ext. Bui.
52, 20 pp., illus.
Hills, J. L.

1904. the maple sap flow. Vt. Agr. Expt. Sta.
Bui. 105: [1931-222, illus.
Hitchcock, J. A.

1928. economics of the farm manufacture of
maple syrup and sugar. Vt. Agr. Expt. Sta.
Bui. 285. 96 pp., illus.

1929. COST AND PROFIT IN THE SUGAR ORCHARD.
Agr. Expt. Sta. Bui. 292, 19 pp., illus.

1937.

Vt.

THE GRAZING OF MAPLE SUGAR ORCHARDS.
Vt. Agr. Expt. Sta. Bui. 414, 14 pp., illus.
HUFFMAN, R. E., DeVault, S. H., and Coddington, J. W.
1940. an economic study of THE MAPLE PRODUCTS
industry in GARRETT COUNTY, MAR^XAND.
Md. Agr. Expt. Sta. Bui. 431. pp. 16.5-215, illus.

MAPLE SIRUP PRODUCERS MANUAL

135

HuTCHiNs, Mrs. H.

1900. PIONEERING |IN MICHIGAN) — GATHERING SAI'
AND GOING TO MILL. (A poem.) In (Mich.
Hist. Comm.,1 [Mich.) Hist. Collect. (1897-9S)
28: 638-640. (Collections and Researches
made by Michigan Pioneer and Historical Soci-
ety.)
Jones, c. H.

1938. the exclusion of lead from maple sap.

(PROGRESS REPORT.) Vt. Agr. Expt. Sta. Bui.
439, 7 pp.
and Bradlee, J. L.

1933. the carbohydrate CONTENTS OF THE MAPLE
TREE. Vt. Agr. Expt. Sta. Bui. 358, 147 pp.,
illus.

Kelley, M. C.

1933. SAP, SUGAR AND SHEEPSKINS. Amer. Forests
39: 114-115, 144, illus.

1936. SAVING THE SUGAR ORCHARD. Amer. Forests
42: 221, 242, illus.

MclNTYRE, A. C.

1932. THE MAPLE PRODUCTS INDUSTRY OF PENN-
SYLVANIA. Pa. Agr. Expt. Sta. Bui. 280, 47
pp., illus.

McKay, A. W.

1922. MARKETING VERMONT MAPLE-SAP PRODUCTS.
Vt. Agr. Expt. Sta. Bui. 227, 48 pp., illus.

Marvin, J. W., and Erickson, R. O.

1956. A STATISTICAL EVALUATION OF SOME OF THE
FACTORS RESPONSIBLE FOR THE FLOW OF SAP
FROM THE SUGAR MAPLE. Plant Physiol. 31:
57-61.

[Maryland University Agricultural Extension
Service and Garrett County Maple Producers
Association.)

1931. MAPLE SUGAR AND SIRUP RECIPES. Md. Univ.
[Agr.l Ext. Cir. 87, 9 pp.

Moore, H. R., Baker R. H., and Diller, O. D.

1948. THE FARM SUGAR BUSH. Ohio Farm and
Home Res. [Ohio Expt. Sta.[ 33 (251): 40-45,
illus.
Morrow, r. r.

1952. consistency in sweetness and flow of
MAPLE SAP. Jour. Forestry 50: 130-131.

MURPHEY, F. T.

1937. THE MAPLE SYRUP CROP. Pa. State Col. Ext.
Cir. 186, 28 pp., illus.

1947. MAKING MAPLE SYRUP. Pa. State Col. Ext. Cir
310, 36 pp., illus.

Nearing, H., and NEARING, S.

[1950.1 THE MAPLE SUGAR BOOK. 271 pp., illus. New
York and Toronto.
ORMSBEE, C. O.

1920. EVERY STEP IN MAPLE SUGAR MAKING. Rural
New Yorker 79: 343-344, 409, 519-520, 576, 625,
illus.

1923. THE MAPLE SUGAR INDUSTRY. THE TREE THAT
MADE VERMONT FAMOUS, AND HOW ITS DE-
LECTABLE JUICE IS HARVESTED. Sci. Amer.
129: 176, 214-215, illus.

ORTON, V.

1941. SUGARING. Sat. Evening Post 213 (38): [14]-
15, 104, 106, 108-109, illus.
PEARL, M.

1952. VERMONT MAPLE RECIPES. 87 pp., illus. Bur-
lington, Vt.
Peffer, E. L., and BLAIR, M. G.

1949. TESTING of hydrometers. [U.S.I Natl. Bur.
Standards Cir. 477. 9 pp., illus.
Pennsylvania Department of Forests and Waters.
Division of Forest Research.

1952. "common trees" of PENNS'i'LVANIA. 55 pp.,
illus. [Harrisburg.)

ROBBINS, P. W.

1944. SMOKE IN THE SUGAR BUSH. Counti-y Gent.
114(2): 22, 25-26, illus.

1949. PRODUCTION OF MAPLE SYRUP IN MICHIGAN.
Mich. Agr. Expt. Sta. Cir. Bui. 213, 28 pp., illus.

SCHULER, L., and SHERMAN, R. W.

[n. d.) MAPLE SIRUP MARKETING IN GEAUGA COUNTY,
OHIO. Ohio State Univ.. Dept. Agr. Econ. and
Rural Sociol. AE 327, 16 pp.

Science 98:

Country

SEARS, P. B.

1943. GRAZING VERSUS MAPLE SYRUP.
8,3-84.

SMITH, R. H.

1919. TAPPING NATURE'S SUGAR BUSH.
Cfent. 84 (4): 13, 63-64, illus.

Snell, J. F.

1913. THE ANALYSIS OF MAPLE PRODUCTS. I. AN
ELECTRICAL CONDUCTIVITY TEST FOR PURITY
OF MAPLE SYRUP. Jour. Indus, and Engin.
Chem. 5: 740-747, illus.

1916. THE ANALYSIS OF MAPLE PRODUCTS. V. MIS-
CELLANEOUS OBSERVATIONS ON MAPLE SYRUP
[TO FIND] NEW METHODS OF DETECTING ADUL-
TERATION. Jour. Indus, and Engin. Chem. 8:
144-148.
and ScOTT, J. M.

1914. THE ANALYSIS OF MAPLE PRODUCTS. III. THE
RANGE OF VARIATION OF ANALYTICAL VALUES
IN GENUINE MAPLE SYRUPS. Jour. Indus, and
Engin. Chem. 6: 216-222.

SPENCER, J. B.

1923. THE MAPLE SUGAR INDUSTRY IN CANADA.
(THIRD EDITION.) Canada Dept. Agr. Bui. (n.s.)
30, 43 pp., illus.

sy, a. p.

1908. HISTORY, MANUFACTURE AND ANALYSIS OF
MAPLE PRODUCTS. Franklin Inst. Jour. 166:
249-280, 321-352, 43.3-445, illus.

136

AGRICULTURK HANDBOOK i:54, U.S. DEPT. OF AGRICULTURE

TOWLE, D. S.

1946. SAP WEATHKR. Anier. Mus. Nat. Hist., Nat.
Hist. 55: IU0I-U2. illus.
Vermont Department of Agriculture.

1941. \ermont maple sugar and syrup. vt.
Dept. Afcr. Bui. .38, 41 pp., illus. (Rev.)
WEBBER, L. E., and SeeLEY, L. E.

1950. OPERATION OF MAPLE SAP EVAPORATORS US-
ING OIL BURNERS. N.H. Enpin. Expt. Sta.
Engin. Pub. 9, 7 pp., illus. _
WEIR, J. G.

1982. CARE OF THE SUGAR BUSH. Vt. Agr. Col. Ext.
Cir. 71, 15 pp., illus.

1933. SUGGESTIONS FOR MAKING HIGH QUALITY MA-
PLE SYRUP. Vt. Agr. Col. Ext. Cir. 73, 16 pp..

WILLITS, C. O. .-

19.38. THE PAINTING OF SAP BUCKETS AND OTHER
EQUIPMENT USED IN THE PRODUCTION OF MA-
PLE SYRUP. N.Y. State Agr. Expt. Sta. Cir.
182, 4 pp.

and TRESSLER, C. J., JR.

1939. THE PREPARATION AND PAINTING OF MAPLE-
SUGAR- PRODUCING EQUIPMENT. Jour. Agr.
Res. 59: 151-158, illus.

WINCH, F. E.

11954.1 TAP YOUR TREES. N.Y. State Col. Agr.
ICornelll Ext. Serv. |5| p. folder, illus. (Coop.
Ext. Work in Agr. and Home Econ.)

Woods, J. B.

1945. MAPLE SUGAR OR MAPLE LOGS?
ests 51: 544-.547, illus.

Amer. For-

■& U..S. GOVERNMENT PRINTING OFFICE: 197B O— 597-10!

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