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Washington, D. C. July 3, 1923

PRODUCTION OF SIRUP FROM SWEET POTATOES.

By H. C. Gore, Chemist in Charge, Fruit and Vegetable Utilization Laboratory,
b H. C. REESE, Assistant Development Engineer, and J. O. Rrep, Assistant
Development Engineer, Office of Development Work, Bureau of Chemistry.

CONTENTS.
Page. Page.
Sweet-potato by-products__________ 1 General properties of sweet-potato
Commercial possibilities for sweet- fy PEER tee ee 2
PaLhOm HIRU— =. 8 ee 2 ee 3 | Composition of sweet-potato sirup__ 32
Experimental work on sweet-potato Composition of sweet-potato pomace_ 32
DS De eS oe ee eee APPS ummeary + 3 Se ee oa 33
Production of sweet-potato sirup on
Eansmereial scale. - s—=-= Ss 20

SWEET-POTATO BY-PRODUCTS.

No sweet-potato by-products industry exists at present in the United
States where sweet potatoes rank second in importance of all vegeta-
bles grown. Consequently a large part of this crop is lost each year
from decay. When good growing conditions prevail up to harvest
time, a great many potatoes become overgrown, forming so-called
“jumbo” potatoes. These oversized potatoes, which often constitute
40) per cent of the entire crop, have the same composition as roots
of the standard market sizes, but they are of less value for shipping
to distant markets and for canning. The development of profitable
methods for converting such potatoes into useful products is there-
fore of great importance. While the production of oversized po-
tatoes is large, the production of undersized potatoes is usually
small. The small potatoes are used largely for seed purposes.

Sweet potatoes are richer in carbohydrates, especially starch, than
any other vegetable commonly grown. For this reason they are a
possible source of many products containing or derived from starch,
such as potato flour, dehydrated potatoes, starch, sirup, alcohol,

1 The work reported in this bulletin was conducted cooperatively by the fruit and vege-
table utilization laboratory and the office of development work. The laboratory process
for producing sirup from sweet potatoes was worked out by H. C. Gore, who also assisted
in the production of sirup at the experimental plant installed at Fitzgerald, Ga. The
equipment for the production of the sirup at Fitzgerald was designed and installed by
the members of the office of development work, who also determined the production cost
and the market value of the sirup. This part of the project was conducted under the
supervision of H. E, Roethe. The Union Cotton Oil Co., Fitzgerald, Ga., gave the use of
its plant for making the sirup on the commercial scale, and C. A. Newcomer, secretary
and treasurer of the company, cooperated with the investigators during the field work.
The States Relations Service of the Department of Agriculture and various State exten-
Sion directors submitted helpful comments and tested the sirup produced. ‘ Manufacturers
and jobbers of sirups, confectionery, soft drinks, cookies, biscuits, etce., tested samples of
Sweet-potato sirup and gave their opinions on its quality and possible use,

37996°—23 1

2 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE,

vinegar, breakfast foods, and various kinds of feeds. Dr. G. Wea
Carver, of Tuskegee Institute, has prepared all of these products,
as well as many others,? from sweet potatoes.

6, 1870, to Charles Delamarre, of New Orleans. In his process the —
peetoes were cooked and then reduced to a pulp by being passed —
etween wooden rollers. Eight pounds of crushed malt to each 100

sweet-potato flour, which sold readily at satisfactory prices, was made
there by the following method: F reshly harvested sweet potatoes
were thoroughly scoured by brushing machines which removed prac-
tically all of the peel. They were then sliced and conveyed to a drier
which consisted of a series of special drying floors placed one above
another. Here the slices were dried in an ascending current of hot
air. The slices were fed in at the top of the drier and were dropped
through from floor to floor as they were dried, by opening succes-
sively the shutters composing the floors. The dried product was
ground while still hot and was very finely bolted. Production ceased
about 1906, owing to the lack of démand for the flour,

The Williams Co., of Greenville, S. C., during 1916 produced
three sweet-potato products—a crumblike product known as yam
nuts, a sweet-potato flour flake, and a sweet-potato flake. Manufacture
was protected by United States patents 1238371, 1238372, and 1238373.
The general method employed in these three processes was to mix
the steamed peeled potatoes with flour, salt, and yeast, allow this
dough to ferment, add a large quantity of cooked potatoes to the _
sponge thus produced, and let it ferment. It was then made into _
loaves and baked. The loaves were allowed to cool, after which they

* Tuskegee Institute, Ala., Buil. 38, 1922; “Two great money crops of the South,”
address at the Voorhees Farmers’ Conference, Feb. 16, 1921, Denmark, S. C., published by
the Voorhees Press,

Se ee eee ee YS eee

; PRODUCTION OF SIRUP FROM SWEET POTATOES. 3

were worked up into the crumblike product, flour, or flakes. Produc-
tion, however, was unprofitable and eventually ceased.

The manufacture of sweet-potato flour by the flake process was
taken up by Mangels and Prescott of the Bureau of Chemistry dur-
ing the spring of 1919.2 Their method was as follows: The potatoes
were washed, steamed under 15 pounds pressure for 15 minutes, and
then dried in a drum drier of the type extensively used abroad in
treating Irish potatoes. The drier consisted of two revolving drums
supplied with steam at from 35 to 53 pounds pressure. The cooked
potato was spread out on the cylindrical surface of the drum by
means-of smaller auxiliary rollers, dried rapidly, and then removed
by scraper knives. The flakes thus obtained were ground into flour.
This process could not be applied to sweet potatoes on account of the
difficulties encountered in securing a product of attractive color and
flavor and because the flour obtained was so hygroscopic that it
hardened upon storage, forming gummy cakes.

The study of McDonnell* on the manufacture of sweet-potato
starch has great general technical value. Despite his satisfactory
results, the simplicity of the process, and the favorable reports on the
market value of starch, commercial development of sweet-potato
starch manufacture has never been undertaken.

COMMERCIAL POSSIBILITIES FOR SWEET-POTATO SIRUP.

_ From 5 to 6 gallons of sweet-potato sirup produced by the Bureau
of Chemistry was sent to each of many manufacturers of sirup and
various products made with sirup to obtain their opinions as to the
quality and commercial application of the sirup. Most of these
manufacturers submitted a report.

The consensus of opinion was that the sirup produced during 1922
was superior to that which had been produced during the preceding
year. There was, however, a wide variation of opinion as to the
quality of the sirup. Some claimed that the sirup was not sweet
enough; others that it was too sweet. Some thought the color was
too dark; others that it was good. Some reported that the sirup
had a sweet-potato taste, which was objectionable; others stated that
the sweet-potato taste in the sirup was hardly noticeable, and even
if present would not be objectionable. Some said the sirup was

either too thin or too thick; others that its consistency was about
right. This difference of opinion was to have been expected. Each
manufacturer measured the quality of the sirup by the requirements
of his product or of his particular method of manufacture.

In several cases the sirup fermented readily. This may not be
a serious objection, as it probably may be avoided by concentrating
the sirup to a certain degree Brix. This, however, would have to
be determined by a series of tests. The claim has also been made
that the sirup will scorch when cooking on a fire before it reaches a
temperature of 250° F.

The rephes of the manufacturers show that the qualities of the
sirup limit its field of use. Because of its color the sirup could not
be used generally in the manufacture of candies other than colored

ge eo tzctare of sweet-potato flour by the ‘ flake’ process,’ Chemical Age, 29 (1921):
4“The manufacture of starch from sweet potatoes,” S. C. Agr. Expt, Sta., Clemson
College, S. C., Bull. 136, April, 1908.

4 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.

candies, such as caramels, taffy, and kisses, and those which do no
require a grain. The same holds true in baking. Doubtless the
sirup would make a good cooking and table sirup in the household.
It probably will never come into general use as a table sirup because
of its characteristic taste, although it might find favor with those
who like that taste.

Sweet-potato sirup has qualities which make it a valuable blend
for other sirups. Like glucose, at present the chief material for
blending, sweet-potato sirup prevents crystallization of cane sirup.®

The commercial application of this sirup is limited by its cost of
manufacture as compared with that of other sirups. If sweet-potato
sirup could be manufactured at a lower cost than:the other sirups,
uses would readily be found for it. With the present method of
manufacture and with the present market value of the other sirups,
however, this is impossible. It may be that in times of emergency,
when the price of sugar and sirups soars, sweet-potato sirup can be
manufactured at a profit. It is doubtful whether sweet-potato sirup
could be used as a substitute for glucose at its present low cost.

EXPERIMENTAL WORK ON SWEET-POTATO SIRUP.

PRELIMINARY WORK.

During the fall and winter of 1920 the Bureau of Chemistry ©
experimented with the sirup making from sweet potatoes in the
laboratory. The ease with which sirup could be prepared was dem- —
onstrated and the nature of the equipment necessary for its pro-
duction was determined.® The process for the production of sirup
from sweet potatoes thus developed gave indications of possessing
promising commercial possibilities. Field operations were therefore
begun in the spring of 1921 and continued during the first part of
1922, with a view to studying the commercial application of the
process, special attention being given to the determination of the cost —
of manufacturing, the market value, and the possible uses of the
sirup. Fitzgerald, Ga., was selected as the most satisfactory place for
the experimental plant.

A few hundred gallons of sirup of fair quality was manufactured
there in 1921. Small lots of the sirup were distributed among the —
larger manufacturers of sirups, confectionary, soft drinks, cookies,
biscuits, etc.; for expression of opinions on its quality, market value,
and possible uses. It then became evident that a still better sirup
was needed to meet trade requirements. With this in mind, further
laboratory work was done.

At the conclusion of these laboratory tests the experimental work
at Fitzgerald was resumed during the early months of 1922. The
plant was remodeled and numerous improvements were made in the
installation. About 300 gallons of sweet-potato sirup was produced.

5 Recent laboratory tests have shown that sweet-potato sirup can be used to prevent
crystallization in cane sirup. In the tests crystallization was much retarded by adding
20 per cent by weight of sweet-potato sirup (75.86° Brix) to the cane sirup and entirely
prevented by the use of one-third by weight of sweet-potato sirup, the composition of the
resulting mixture being three-fourths cane sirup and one-fourth sweet-potato sirup. Two.
samples of cane sirup were used in the tests. One was Georgia cane sirup of 75.02°
Brix, apparent purity 61.35; the other was Louisiana cane sirup of 73.8° Brix, apparent
purity 72.66, The tests were made by mixing the cane sirup with different quantities of
sweet-potato sirup, inoculating each mixture with a trace of powdered sucrose and letting
it stand in cold storage for several months.

6“ Preparation of sweet-potato sirup,’’ Chemical Age, 29 (1921): 151.

PRODUCTION OF SIRUP FROM SWEET POTATOES. 5

This sirup was distributed in much the same manner as that pro-
duced during the preceding year.

WORK AT FITZGERALD, GA.

BUILDINGS.

The apparatus used in conducting the experimental work on the
production of sweet-potato sirup on a semicommercial scale was in-
stalled in a frame building covered with corrugated sheet iron and
provided with a cement floor (Fig. 1). The engine room had the

Fic. 1.—Plant at Fitzgerald, Ga., which was used for conducting experiments on
the manufacture of sweet-potato sirup on a semicommercial scale.

same construction. The boilers for generating the steam were built
out in the open, but were covered with a roof made of wooden rafters
covered with corrugated iron sheathing. The potatoes were stored
in a frame building mounted on wooden piles. The walls were made
of slab boards over which pebble-finished tar paper was spread verti-
cally, battens being used to cover the laps. The roof of the building
was made of rafters covered with slab boards overlaid with pebble-

coated tar paper.
PLANT LAYOUT.

The layout of the experimental sweet-potato sirup plant (Fig. 2)
shows the apparatus necessary for the production of the sirup, the
floor space required by the various pieces, and their placing. A plant
of this size is large enough for an average daily production of 50
gallons of finished sirup. Its capacity could be greatly increased,
however, by the addition of a few other pieces of equipment.

APPARATUS.

A detailed statement of equipment used is given in Table 1.

6 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.

TABLE 1.—Apparatus used in the manufacture of sweet-potato sirup.

Revo-
Item |[Num- Fl Hors scene) atk
em . oor ‘ TSse- * ermin-| Uni
No. ik Kind. space. Weight. ower. Capacity. Pate of | value,
vat i driving
pulley
Feet. |Pounds.
1 til aWashers. tae eae 64 by 11--. 850 1 | 150 bushels per hour. .. 90 $300
2 E-|-Mashitank== ND Yale oes 1, 200 Sy il 4200 eallons ste eecee 72 350
3 | 1 | Hydraulic press. ...- 4by11....| 2,800 14 | 17 bushels per hour. ..- 120 375
4 1 | Evaporator. -......- ARDY 182.2) “Aso0nlssaoee 40 boiler horsepower...|......-- 350
5 1°] Cooling: tank. 2222.2 53 by 63..- 175 4°.) 7550 'gallons ss. s2ee 90 55 3
6 1 | Filter press. ........ 4} by f4=5-| °2,800) |e2 sc ese- pe plate, 18-inch: |22s2--2— 400
| rame.
7 | 1| Flavoring and bot- | 74 by 7}... OO | reas 50-gallons . 532: 35 >=} eee 125
tling kettle.
8 1) aD rierse: a eee 144 by 113.| 1,500 14 | 60 square feet (area)...| 2,000 225

INSPECTION TABLE

CAPPING

« QOHP LNGInNE

Lncine Room

FINISHING

80H P BOILER

OWL RNC AD
TANK
ty

S
&
&
x
8

Q
: (iP
eS
FH Ip
‘ q
eS

Fig, 2.—Layout of experimental sweet-potato sirup plant, Fitzgerald, Ga.

PoMACE DRIER

PRODUCTION OF SIRUP FROM SWEET POTATOES. 7

Fic. 3.—Sweet-potato washer in operation.

WASHER,

A standard-make, rotary-screen cylinder washer (Fig. 3) was used
to remove the dirt, sand, etc., from the sweet potatoes before they
were placed in the mash tank for steam blanching. <A ‘$croll-shaped
pipe, running from one end of the washer to the other, carried the
potatoes through the machine. The turning over and over of the
cylinder caused the potatoes to rub against one another. This rub-
bing action, together with a spray of water from a perforated pipe,
which extended through the cylinder parallel to its axis, thoroughly
washed the potatoes.

The driving pulley of the washer was driven at 90 revolutions per
minute, which made the cylinder revolve approximately 25 times
a minute. With this operating speed, 150 bushels of sweet pota-
toes an hour could be washed. The washer was installed out of
doors to save installation expenses, especially the cost of sewer con-

nections.
MASH TANK,

A large wooden tank, 7 feet in diameter and 5 feet deep, outside
dimensions, was used for the steam blanching and the subsequent
mashing of the sweet potatoes (Fig. 4). It was made of 3-inch
cypress staves dressed down to 2? inches and had a capacity of ap-
proximately 1,200 gallons. Steam for blanching purposes was pro-
vided by means of three-quarter-inch pipes running into the tank at

8 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.

every 90°. The admission of the steam was controlled by means of
valves in each line. Each pipe had a single row of small holes, 1-inch
spacing between perforations, so that the steam would be equally
distributed in the tank. The perforations were turned toward the
bottom of the tank to prevent plugging.

The tank was equipped with a wooden agitator to break the pota-
toes into.a mash after the steam blanching and also to thoroughly
disseminate the malt through the mash during the conversion. The
agitator shaft, made of oak, was 6 inches square. To this shaft were
fastened four sets of oak paddles, 33 inches long, with a cross section
34 by 6 inches (Fig. 5). The 83-inch face of the bottom set of pad-
dles was cut down as a propeller to form a good cutting edge and to
beat the mash up from the bottom of the tank as the agitator rotated.
The 33-inch face of each of the other three sets of paddles was cut
down into a wedge or V shape, to give the paddles a good cutting edge,
thereby facilitating the breaking up of the potatoes into the mash.

Fic. 4.—Mash tank (exterior).

pee oY

The agitator was driven by
means of a beveled pinion and
gear, ratio 1 to 4, giving the
agitator a speed of 18 revolu-
tions per minute. Aside from
the large starting torque re-
quired, this arrangement gave
satisfactory service. The po-
tatoes could be broken into a
mash within 8 or 10 minutes.

A quick opening, 3-inch
valve, fastened to the side of
the tank near the bottom,
made it possible to draw off
the heavy mash rapidly. The
tank was fitted with a galva-
nized-iron cover with hinged
doors on either side.

;

HYDRAULIC PRESS.

The hydraulic press (Fig. Fic. 5.—Mash tank (cross section).

6) used to press the wort from

the pomace was of the type employed in the manufacture of grape
juice. As originally designed, the press called for the use of 28-inch
racks. To meet the demands at Fitzgerald, the pressing area was
enlarged to handle racks 48 by 36 inches. With this arrange-
ment, the mash from a 50-bushel batch could be pressed in three
hours.

A truck ran on a track from the press to the mash tank. After
being loaded with layers of pulp and racks the truck was pushed
to the press, where the plunger lifted it against the pressure head,
forcing the wort from the pomace. The wort drained into a gal-
vanized-iron catch tank, 6 by 3 feet by 1 foot deep, which was set
in between the tracks. .

From the catch tank the wort. was pumped to an overhead tank,
or reservoir, from which it could be drawn as desired into the evapo-
rator. .

EVAPORATOR.

_A horizontal, continuous open-type evaporator made of maple
(Fig. 7) was used in concentrating the wort into sirup. It was 15
feet 8 inches long by 30 inches wide by 12 inches deep. A baffle
wall extended from one end down through the middle of the evapo-
rator to within 16 inches of the other end. The inside of the evapo-
rator was lined with 24-gauge galvanized iron. Heat was furnished
by two sets of three-fourths-inch copper coils of three pipes each,
placed side by side on the bottom of the evaporator. The evaporator
required 40 boiler horsepower at 80 pounds gauge pressure. This
corresponds to approximately 1,200 pounds of water evaporated per
hour. The coils were so installed in the evaporator that the incom-
ing sirup could be heated by the exhaust end of the coils. As the
sirup became more concentrated it was heated by hotter steam. In

37996 °—23 2

10 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.

Fie. 6.—Hydravlic press in operation.

other words, the sirup could be heated gradually and reach its
highest temperature at the point of discharge.
The steam given off by the sirup during the evaporating operation

was conducted to the outside by a large fume pipe, 18 inches in di-
ameter, made of hard pine.

COOLING TANK.
After evaporating the wort into crude sirup it is necessary to

allow the product to cool so that certain salts may separate. To
cool the sirup a large tank was built of 24-gauge galvanized iron

j
1
2
;
3
3
:
3
:

ee
y |
if

PRODUCTION OF SIRUP FROM SWEET POTATOES. tt

(Fig. 8). The tank was 5 feet in diameter and 4 feet deep and had
a capacity of approximately 550 gallons. The outlet to the filter
press was 1$ inches.

The tank, mounted on a platform about 18 inches high, was
clamped securely to the platform by four 43-inch iron rods, so
shaped as to fit over the top edge of the tank. The tank was also
equipped with a mechanical agitator. On the agitator shaft, a steel
bar 11 inches in diameter, were placed four sets of paddles made of
2 by 2 inch oak stock with one face cut down lke a propeller to
give a good stirring action. ‘Two sets were made to throw the sirup
toward the bottom of the tank and two sets were made to throw the
sirup upward. In this manner the thrusts set up by the paddles as
they came in contact with the sirup neutralized one another. To
fasten the paddles to the shaft, a hole 1,3; inches in diameter was
bored where the two paddles in one set overlapped. The paddles
were then placed in position on the shafting and clamped to the
shaft by means of four three-eighths-inch bolts.

The agitator was driven by a beveled pinion and gear, ratio 1 to 4,
giving the agitator a speed of 22 revolutions per minute.

FILTER PRESS.

After the cooling
operation the sirup
was filtered in an 18-
inch, 18-frame, lug
feed, outside de-
livery, cast-iron fil-
ter press (Fig. 8).
Twill cloths were
used in conjunction
with kieselouhr as a
filtering medium.

The rectangular
catch tank was made
of 24-cauge galva-
nized iron, 61 feet
long by 2} feet wide
by 12 inches deep.
The filtered sirup i tae Ge a
was stored in this ot) eet Poe BS

tank until it was to CS ptt Cad coho PY
be evaporated, when
it was pumped to the
evaporator.

FLAVORING AND BOTTLING
KETTLE.

For flavoring the
sirup or for putting
it in bottles a steam- ne ae a a eae
jacketed copper ket- : MOE Cucentratine the Bert and tae fitered sire col

12 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.

tle was used (Fig. 9). As described on page 20, the sirup to be
bottled or flavored was carried to and poured into the flavoring
and bottling kettle. After it had been heated it was flavored or
bottled. The maximum diameter of the kettle was 30 inches, its
depth was 24 inches, and its capacity was 50 gallons. It was mounted
on an iron stand, bolted to a platform 73 by 43 feet by 53 feet
high. The sirup ‘Was discharged from the ‘kettle through a 14-inch
outlet, reduced to an inch line. For putting the sirup in cans a
half-inch connection was made. For bottling the sirup a series of
T-pipe fittings, in which wooden spigots were screwed, was used.
The bottles were placed under the spigots.

DRIER FOR POMACE,

For drying the pomace from the pressing operation a plenum
chamber drier was constructed (Fig. 10). The air was heated by a
set of steam coils inclosed in a wooden housing lined with tin, and
was blown into a chamber under the pomace. The heated air pass-
ing up through the pomace dried it.

The steam coils for heating the air were made of 1-inch pipe, in
sections, each section containing 18.6 square feet of radiating sur-
face. There were 10 sections of coils in the heating unit, giving a
total of 186 square feet of radiating surface. With the steam pres-
sure used, the coils heated 1,930 cubic feet of air per minute from
60° to 160° F. The air passed over the coils at a velocity of 360 feet
a minute.

Fig. 8.—Cooling tank and filter press.

PRODUCTION OF SIRUP FROM SWEET POTATOES.

Fic. 9.—Flavoring and bottling kettle.

The coils were so arranged that five sections secured steam from
one header line and discharged into one line, while the other five
sections were fed by another header and discharged through a sep-
arate line. The sections on one header line were alternate d with the
sections on the other. The sections were also staggered in such a
manner as to form baffles to the air as it passed through the heating
unit, thus increasing the efficiency of heat transmission. The coils
were incased in a housing built of siding, lined with tin. The hous-

14 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.

Fig, 10.—Drier used in drying the pomace.

ing was constructed in three parts, two sides and the top, the cement
floor forming the bottom. It was built in this way to take it port-
able. The housing was 3 feet high, 32 feet wide, and 5% feet long.

One end of the housing was connected to the eye or intake ‘of a
blower fan by means of a rectangular converging section made of
24-cauge galvanized iron. The housing end of the section was 3 by
33 feet, and the blower was 9 inches in diameter. The housing end

ras nailed to the housing, while the blower end was merely slipped
over the intake.

The fan, which was a standard make with cast-iron shell and
steel plate blades, had a 9-inch intake and a 9-inch exhaust. It had
a capacity of 1,930 cubic feet of air at 2,000 revolutions per minute.

The fan discharged the heated air into a chamber under the
pomace. This chamber, built of 1-inch Georgia pine and lined with
valley tin, was 74 feet wide by 84 feet long ul. and 1 foot high.
The cement floor ‘ot the building formed the bottom of the chamber.
The top of the chamber, which made the bed on which the pomace
was placed, was constructed by placing 2 by 4 inch boards across the
top of the chamber every 2 feet, stretching galvanized iron wire sand
screen, 4 meshes to the ineh, over them, and laying a covering of
burlap over the screen. The chamber bed area was 60 square feet,
and the pomace covered it to a depth of approximately 2 inches.

Raw MATERIALS.

The potatoes used at Fitzgerald were of the Porto Rico variety,
the only one available. Cured stock taken directly from a storage
warehouse was picked over by hand immediately before being used,

;
4
*

PRODUCTION OF SIRUP FROM SWEET POTATOES. 15

Sand all decaying potatoes were removed. Very little decay, only

_ from 1 to 2 per cent, was originally present, and this was almost

entirely eliminated as the result of the inspection given.

Pale distillers’ malt of high diastatic power was employed. The
kieselouhr which served as a filter aid was of California origin.

_ Before being added to the mixing tank it was ignited at a low red

heat in cast-iron pans in the fire box of the boiler.

LABOR.

The jabor force at the experimental plant, which was entirely
adequate, consisted of one mechanic and two laborers. A run of
_ erude sirup was usually made on two consecutive days. The next
_ two days were then required for the finishing of the sirup. Thus in
_ four 10-hour days approximately 140 gallons of finished sirup was
produced. By running the apparatus at full capacity approximately
_ 200 gallons of sirup could have been produced, or an average of 50
gallons a day. The mechanic received 40 cents an hour and the two
laborers each 20 cents an hour.
_ The authors acted as the supervising force in directing the opera-
tions. In commercial practice a plant superintendent would be

necessary.
METHOD OF MANUFACTURE.

A flow diagram of the method of manufacturing sweet-potato
sirup (Fig. 11) shows the steps in the operation and the points at
which steam and water were used. It also shows how the different
materials were handled and at what points they were put into the
operation.

WASHING THE POTATOES,

The sweet potatoes were given a visual inspection at the storehouse
and all those showing signs of rot were rejected. As the potatoes
were inspected they were placed in bushel crates. Upon the comple-
tion of the inspection each batch of potatoes was hauled in an auto
truck from the storehouse to the washer.

The washed potatoes were placed in bushel crates. The action of
the washer wore off the ends of the potatoes, thus effectively remov-
ing the withered ends, a possible source of off flavor.

The potatoes were weighed on the platform scales, four crates at a
time, and were then carried to the mash tank. Approximately 50
bushels of potatoes to a run or batch were used.

MASHING,

The potatoes were leveled in the tank and the tank covers were
closed. Live steam was then admitted at such a rate that gentle
streams of vapor passed out between the upper edge of the tank
and the covers. The condensate was allowed to drain off as fast as

it formed through the gate valve, which was opened slightly for
this purpose. This treatment removed from the outer portions of
the potatoes certain extractives which if retained impart a dull green
color and an off taste to the sirup.7?. One and one-half hours’ steam

7 Previous laboratory work (Chemical Age, 29 (1921): 151) had shown that the loss
of sweet-potato solids in the condensed water is very small.

16 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.

cooking was given the potatoes. This softened them so that they
could be easily mashed into a uniform pulp by the stirrer, thus
breaking down the cells sufficiently to secure a good yield of sirup.

Immediately after cooking, water of the same weight as the pota-
toes was dumped into the tank and the stock was reduced to a pulp —
by stirring. With the stirrers still going, the temperature of the
mash was raised to 140° F. by running in live steam. The tempera-
ture was carefully determined by withdrawing large samples of the
mash through the gate valve and testing by thermometer. Readings
of the tank thermometers screwed into the sides of the mashing vat
were not reliable.’ When a temperature of 140° F. (the point at —
which the saccharifying action of malt is most active) had been —
reached a quantity of ground malt, equivalent to one-fifth of 1 per —
cent of the weight of potatoes taken, made into a thin mush with
cold water, was added. The stirring was continued during the addi- |
tion of the malt and for a few minutes thereafter so that it would be
thoroughly incorporated.

The laboratory work had shown that one-fifth of 1 per cent of |
malt was sufficient for the conversion of the undigested starch still
present after heating the sweet potatoes for 14 hours, in the case of
several standard varieties, including Big Stem Jersey, and that one-
tenth of 1 per cent was sufficient for the Porto Rico and Nancy Hall
varieties. In the field work one-fifth of 1 per cent was used. Diges-
tion of the starch was complete in from one-half to three-quarters
of an hour, the end-point taken being when no color was given. when
a drop of a portion of the filtered liquid was added to a dilute solu-
tion of iodin in potassium iodid. The mash was then ready for
pressing.

ee ee

PRESSING.

In pressing the hot pulp was made up in the form of layers from
2 to 3 inches thick between racks and cloths. The press cloth was
just large enough to inclose the pulp completely.

The procedure in laying up the pulp was as follows: The press
truck was wheeled under the quick-opening valve of the mash tank
and a rack was placed on the pressure platform. On this the form
was placed and over it was spread the press cloth, with its edges
parallel to the adjacent sides of the form. The center portion of the
cloth was then filled with hot pulp so as to fill the form, and the edges
of the cloth were folded over, forming the first press cake. The
form was then removed, a rack was placed on the press cake, and
the form was placed on the rack. Another layer was then built.
From 10 to 14 layers constituted a cheese.

When loaded the truck was pushed into the press. Cooked sweet-
potato pulp drains so readily that a large proportion of the liquid
(technically termed “ wort”) flowed out of the cheese before the appli-
cation of any pressure except that caused by the weight of the layers
of the cheese. As it flowed off the wort was collected in a galvanized
iron tank on the floor between the mash tub and the press, from which

Ly pe coal hy Alene ea ARMAS

an oe ene

8 This was due, in part at least, to the effect of the temperature of the tank walls on
the armored thermometer bulb. The tank walls were thicker than was anticipated when
the thermometers were ordered, and the bulb did not project far enough into the tank to
eliminate the influence of the tank-wall temperatures.

a
>
:

PRODUCTION OF SIRUP FROM SWEET POTATOES. 17

it was pumped to the supply tank of the evaporator. The pressure

_ was applied gradually.

In pressing the racks and press cloths tended to slip out of place,
owing in part to the lack of guides to make sure that the ram
ascended vertically, and in part to the fact that the galvanized wire
racks did not maintain their position as well as wooden ones. It is
believed that this difficulty could be overcome by the use of wire
cloth of coarser weave. It was overcome in the experimental work
by placing a series of wooden frames around the cheese as it was
being formed. Three frames, with sides from 6 to 8 inches high,
were superimposed, fitting one on another, by the use of cleats. Dur-
ing pressing the uppermost, and finally the middle, frame was re-
moved. Three cheeses of 10 to 13 cakes each were required for each
50-bushel lot of potatoes.

After pressing the pomace was shaken out of the cloths, which
were then ready to be used again. At the close of each day’s work
the cloths were washed and hung out on lines in the open air to drain
and dry. A batch of 2,500 pounds of potatoes yielded 200 pounds of
dried pomace and required 19 hours to dry. The wort received from
pressing, collected in the catch tank, was pumped to an overhead tank,
which acted as a reservoir, from which it was drawn by gravity to
the evaporator as needed.

EVAPORATION TO CRUDE SIRUP.

The wort contained about 15 per cent of solids. It was pale
yellow, with a faint, sweet taste. It was evaporated to approximately
60° Brix (cold). The most convenient method for operating the
evaporator was to fill it to a mark previously determined by experi-
ment, turn the steam into the coils, and evaporate until the sirup
became so thick that a test portion would. just begin to fall in blobs
or “flake” from the paddle or dipper used in testing. This usually
required from 15 to 20 minutes. The steam was then turned off and
the sirup was discharged. A new batch of the wort was admitted
and the process was repeated. It was expected that the evaporator
could be made to operate continuously. This, however, was imprac-
ticable, as it was impossible to control the feed and steam supply with
sufficient exactness.

The crude hot sirup thus prepared from the potatoes was received
in a collecting tank under the evaporator and was later pumped into
the cooling tank. Here it was allowed to cool and stand until ready
to be converted into finished sirup.

FILTRATION OF CRUDE SIRUP.

The crude sirup is turbid, containing albuminous matter coagu-
lated by the boiling, particles of sweet potato tissue, extraneous mat-
ter, and a small proportion of mineral matter of unknown composi-
tion which separates upon cooling and standing. After the crude
sirup had cooled and stood for about 40 hours, thus allowing time
for the salt to separate, it was mixed with enough cold water to dilute
it to 45° Brix or below. A quantity of ignited kieselguhr equivalent
to 2 per cent of the weight of potatoes taken was first mixed with
this water in the catch tank below the evaporator. The same volume

37996 ° —23—_3

|
}
|

18 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.

P, WATER

SWEET 7) R
POTATOES Poraro i U ]
rel ae pie
J WaREHOUSE| CRATE UU SCALES —oayrl | Neri eee eee ee
a ea 8 k= See Pe oS. (Gebel pees | Ee AR A re
[3

———ee ee
| ee eS eee
y

ao eee ee an aw em eaten

ee oe ee

L.
Cous|Q _, Scapes j }
! ety | OAL, ia 4cKs| gape bh
Nu Up ey Ue pe te 2 ©: _ 10a

TRgPlt-Exnausr

FREIGHT
t= Mes oer oa iene: BSR ay

Ea Ie: | STOCK FEEL

Fic. 11.—Flow diagram for sw

of the crude sirup was then added and thoroughly mixed, and this
mixture was pumped into the cooling tank in which the crude sirup
was stored. The sirup was then pumped into the filter press. The
filtrate was usually clear from the start. A small belt-driven pump
was attached to the delivery tank, with valves so arranged that the
filtrate could be sent either to the cooling tank or to the evaporator,
as desired. The pressure used in filtering was allowed to build up
gradually during the filtration to about 25 pounds. .

Fifty pounds of kieselguhr proved to be nearly enough to fill the
18 frames of the filter press. The filter cake was washed by pumping
cold water in through the feed ports. Laboratory experiments, using
a small filter press of the same type, showed that it was practicable to
reignite and reuse the kieselguhr. This, however, was not done in the
field trials at Fitzgerald.

EVAPORATION OF FILTERED SIRUP.

After being filtered, the sirup was evaporated to the desired
density, using the evaporator employed for crude sirup, thoroughly
cleaned, of course. As the dilute filtered sirup in boiling foamed
more than the crude wort, a special procedure was evolved to over-
come this difficulty. Unless the level of the sirup was kept rather
low in the evaporator, it had a tendency to foam over every time
the freshly filtered sirup was added. When a low sirup level was
maintained, however, the steam gauge at the head of the evaporator
coils became a convenient guide in indicating when to add a por-
tion of the freshly filtered sirup. As the contents of the evaporator
approached the density of the finished sirup, the steam pressure in
the coils gradually increased to 40 or 45 pounds. As the stream
of filtered sirup was slowly added by means of the pump, this pres-

; = oan GUHR | CONTAINERS

PRODUCTION OF SIRUP FROM SWEET POTATOES. 19

a PPING
ACHINE Ay ore

: y : |
i ~ Ea ] 1) Borr. Le j
; a) foes tears |

Caren Tare RRA ARM Jo Poa Dee

al)
a5 SH/PPING

“ae j FREIGHT

| pe

perimental plant, Fitzgerald, Ga.

sure fell promptly to 30 pounds or less, owing to the greater rate
of heat transference from the steam coils to the sirup as it became
diluted. When the gauge indicated 30 pounds the supply of fresh
sirup was cut off. The pressure was then again gradually built up
to 40 or 45 pounds when the operations were repeated, the cycle of
operations requiring about 10 minutes. The sirup was discharged
at frequent intervals, care being taken, however, never to let the
steam coils become exposed to the air.

As in the case of the crude sirup, the approximate concentration
at which to stop evaporation was shown by the flaking of a test por-
tion poured from the testing dipper. This procedure gave a sirup
more dilute than desirable, the Brix when cold being only about
62.5, so that the flaking indication, although very convenient, is by
no means as exact an indicator for the density of the hot sirup as
the Brix spindle recommended by Dale® and others. The sirup
should be concentrated to about 70° Brix (cold).

CANNING AND BOTTLING THE SIRUP.

The finished hot sirup was either allowed to flow from the evapo-
rator directly into the cans or bottles and sealed or it was trans-
ferred to a steam-jacketed copper kettle. Here it was reheated to
the boiling point and drawn off into cans or bottles. The containers
were washed immediately before use and the bottles were heated in
hot water before being filled. When filled they were capped with
the aid of a foot-power capping machine and placed on their sides
to cool, the object being to sterilize the inner surfaces of the seals
by keeping them in contact with the hot sirup.

®U. S. Dept. Agr. Cir. 149, 1920.

BULLETIN 1158, U. 5. DEPARTMENT OF AGRICULTURE.
Dp jh ta L ; .

es
WAREHOUSE| CRATE
cos) a=

EXHAUST

| S70¢K FEED

te Hee mee

[a tere

PRODUCTION OF SIRUP FROM SWEET POTATOES 19

= — — IK ESELGUHR

1 yneHouse
SCALES

CAPPING
MACHINE

CASES

1] Borree
EVAPORATOR | 55), pe

7 7A AAMSS_

\ WAREHOUSE |

S/PPING
| CONTAINERS

| ee

i
eee eee

FREIGHT

| pga, El

Iie. 11.—Flow diagram for Sweet-potaifsiup experimental plant, Fitzgerald, Ga.

Fifty pounds of kieselguhr proved to be nearly enough to fill the
18 frames of the filter press. The filter cake was washed by pumping
cold water in through the feed ports. Laboratory experiments, using
a small filter press of the same type, showed that it was practicable to
reignite and reuse the kieselouhr. This, however, was not done in the
field trials at Fitzgerald.

EVAPORATION OF FILTERED SIRUP.

sure fell promptly to 80 pounds or less, owing to the greater rate
of heat transference from the steam coils to the sirup as it became
diluted. When the gauge indicated 30 pounds the supply of fresh
sirup was cut off. The pressure was then again gradually built up
to 40 or 45 pounds when the operations were repeated, the cycle of
operations requiring about 10 minutes. The sirup was discharged
at frequent intervals, care being taken, however, never to let the
steam coils become exposed to the air.

CANNING AND BOTTLING THE SIRUP.

The finished hot sirup was either allowed to flow from the evapo-
rator directly into the cans or bottles and_sealed or 1t was trans-
ferred to a steam-jacketed copper kettle. Here it was reheated to
the boiling point and drawn off into cans or bottles. The containers
were washed immediately before use and the bottles were heated in
hot water before being filled. When filled they were capped with
the aid of a foot-power capping machine and placed on their sides
to cool, the object being to sterilize the inner surfaces of the seals
by keeping them in contact with the hot sirup.

®U. S. Dept. Agr. Cir, 149, 1920.

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20 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE,
YIELD.

Sweet-potato sirup made in this manner is bland and sweet, with
a distinctive flavor. It is not as sweet as cane sirup, cane-sugar
sirup, maple sirup, honey, or high-grade molasses. <A satisfactory
degree of sweetness is secured, however, by mixing 100 parts of the
sweet-potato sirup with from 10 to 15 parts of any one of the fore-
going sirups. Other flavoring materials, such as imitation maple
flavor and vanillin, were less satisfactory for this purpose.

In flavoring various lots of sweet-potato sirup, the freshly-made
hot sirup was poured into a steam-jacketed copper kettle, the flavor
was added, and the mixture was heated, with stirring, to the boiling
point, when it was drawn off into the containers and sealed.

YIELD.

In the six runs made at Fitzgerald during the spring of 1921, in
which a total of 8,892 pounds of warehoused Porto Rico potatoes
were used, the average yield of crude, unfiltered sirup was 1.55 gal-
lons to each 50-pound bushel of potatoes. This yield was calculated
in terms-of 72 per cent solids in the sirup. During the first part of
» 1922 the yield of finished sirup in the final containers on the same
basis was 1.37 gallons to each 50-pound bushel of potatoes. As no
special pains were taken to secure high yields, this yield no doubt is
low. Attention was paid mainly to the production of sirup of
uniform high quality. In the practical production of sweet-potato
sirup the two most important factors were (a) the use of the proper
quantity of water in mashing, and (0) the technique of the pressing.
Water is required to facilitate the mashing of the potatoes into pulp
by the action of the stirrer arms and to give the pulp the necessary
fluidity so that it will flow from the mash tank and press readily.
All things considered, the best quantity is the equivalent of the
weight of potatoes taken. For best results, the press cakes should
be thin, not more than 3 inches thick when laid up, and should be
of uniform thickness. Sufficient time for drainage while under high
pressure should be allowed.

PRODUCTION OF SWEET-POTATO SIRUP ON THE COMMERCIAL
SCALE.

Although the cost of manufacturing sweet-potato sirup at the ex-
perimental plant at Fitzgerald, Ga., was naturally too high for com-
mercial purposes, the data thus obtained formed the basis for esti-
mates on the cost of manufacturing sweet-potato sirup in an im-
proved plant. The proposed plan for a sweet-potato sirup plant
makes use of the ideas based on improved practices and on the data
and information secured in the experimental semicommercial plant.

The capacity of the proposed plant was set at 100 gallons of plain
sweet-potato sirup per 10-hour day, which is the common working
day in the sweet-potato sections of the South. A plant of this ca-
pacity was taken because in general it would seem to be most prac-
tical with the sweet-potato curing house of average size. Sirup
plants are probably most practical in connection with sweet-potato
curing houses where culls can be utilized for making the sirup.

—

PRODUCTION OF SIRUP FROM SWEET POTATOES. 21

A normal operating season of eight months may be assumed when >
a storage house is used. The potatoes begin to be available about
August 15 and can be kept in good condition up to April 15, when the
rapid rotting caused by high temperatures makes longer storage

‘impracticable. The loss is very small in the early part of the
season, but becomes noticeable during the last two months of the

period. Under favorable conditions the loss from rotting has been

as low as 2 per cent but may, even with normal care, exceed 10 per

cent under less favorable circumstances. An operating season of 192

_ days (8 months of 24 days each) and a shrinkage of 4 per cent have
been taken as a basis for the cost calculations.

It is fully realized that the estimated costs for various items will

vary with different sections and local conditions. Elaborateness of
_ buildings, possible elimination of the curing house, desired capacity

of the plant, and utilization of labor-saving equipment are im-

portant considerations.

LAND AND BUILDINGS.

A lot 100 by 200 feet would provide ample space for a plant of

_ the size here discussed. This would allow for the required build-

ings, for driveways for handling materials and the finished product,

and for a railroad siding.* It is assumed that the plant would be
_ built in a small town, in which case $1,000 would be a liberal esti-
_ mate for the cost of the land.

The following buildings are necessary: A sweet-potato storage

house, the factory proper, an office, and a boiler and engine house.

The size of the buildings can be determined from the plant layout

(Fig. 12). The cost of the buildings is determined by the type of

construction, which in turn is dependent upon the geographical

- location of the plant, as well as upon the amount of money which
is available. Clearly a plant buiit in a southern State need not
_ be as substantial as one built in a northern State. Since most of

the sweet potatoes are raised in the South, however, the plant was

considered as being located in one of the southern States. The type

of construction of the buildings would be the same as that described

on page 5. The office was taken as being made of weather boarding

with a tar-paper roof, the inside of the office finished with ceiling.
The approximate cost of such buildings would be:

SL ag a aa a $3, 500
LLCS pl tela i fet a EY Ee ee ee ee 3, 500
ye En Ra ae 900
i rnereer sansgne! fed ph 900
2S see eS eR Se ei 8, 400

_
rl nN t

LAYOUT FOR PLANT AND APPARATUS.

From the experience and information secured from the experi-
ments conducted at the experimental plant, a plant for the manu-

facture of sweet-potato sirup was designed. The number and size

of the buildings required by a plant of the given capacity may be
determined from the layout (Fig. 12). The type and number of
pieces of apparatus necessary for the manufacture of the sweet-

22 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.

potato sirup on a commercial scale, as well as the floor space required
by the various pieces of equipment and the arrangement of the dif-
ferent pieces 1n their relation one to another, are shown in Figure 13.

il WHOALV TS
S
NS Se K
| 3 bd N |
| &qw S Q
y ck ©
Na aS xz
N 9 eQ
NX y < ey _ ese Wy
®) & Q e Ne g Q
x x S < x
Seu ee S 8
Jos Ds os |
{ BN S)
{
|
|
e e
8
s |
| i !
x =
y . ct e
:
| x |
>
| :
=

|
|

S/DING

ole ese a

|
i

RAILROAD
Fig. 12.—Layout for proposed sweet-potato sirup plant.

BELT Conveyor

STORAGE HOUSE

8
S
&

PRODUCTION OF SIRUP FROM SWEET POTATOES. 23

—— — 5 —a

Eee ———— —
Sao Te =
4 AS Ue 4 STORAGE FOR

— MALT ANDO KIESELGUHR
imzzulee Fomcsa i |
a 4 2 = 4
Soe A “es «af 1

STORAGE FOR
CANS, BOTTLES, BOXES £7C

STORAGE FOR

| | fet |

gs : FINnisHfO PRODUCT
Finish LVAPORATOR N @)
2 ACHING AND
Machine. seins BE:
es ——— s_-—— [a SEES

Fig. 13.—Arrangement of equipment in proposed sweet-potato sirup plant.

APPARATUS.

- Some of the apparatus used in the proposed plant is of the same

_ size and design as that used in the experimental plant. These are

_ the potato washer, mash tank, hydraulic press, evaporators, filter

_ press, and flavoring kettle (pp. 7-12). Two larger cooling tanks are

_ substituted for the smaller cooling tank, and an additional evap-

orator is provided for handling the filtered sirup. The following

- additional apparatus is necessary in the construction of a plant of
_ the capacity of the one proposed:

TABLE 2.—Additional apparatus in proposed plant.

Num- per =e
Ttem . Floor : Horse- - ! Unit
Kind. space. Weight. power. Capacity. aoe value.

Feet. Pounds.

> i 1 | Endless belt con- | 24 by 55..- 550 1 | 23feet per minute ..... 15 $17
a veyer. bad

~ 2 1 | Hopper scales....... 3 hy! >. 5: VET aes ZO DUSNOISS se saat oo ofa oo 200

a 3 iy Pe OVALOT = se. 3 by 10.... 275 1 | 104feet per minute..... 20 215

a 4 i} measunne tank -.--.|....-..2..-- (SS Ge ee oe ee Aer 75

. 5 2 | Cooling tanks. ...... 7 by 74...- 200 apa mallons-* 2.) 24... | 90 225
6 tol Maxam hank: -2 22) 3,by4s-2.. 40 Nene oat 125 gallons. .....--.... Seeeeece 12
7 1 | Evaporator. ........ Se DY18-5<)) 1,950. |. 222... 2 40 boiler horsepower -...|......-- 350
8 1 OUGE 2 ses fic tea: Sia Soya er. ee: Rit tek a |=» DEEN eS eee ee 500
9 1 | Electric motor. .....| 14 by 2.. 550 0D Rs ae oe eee Oe 675 150

ENDLESS BELT CONVEYER.

The endless beit conveyer for carrying the sweet potatoes from the
storehouse to the potato washer is a standard type. The belt is 24
inches wide and is approximately 55 feet long. The shape of the
supporting idlers gives the belt a concave surface. Power is secured
from an electric motor and countershaft. The driving pulley makes
15 revolutions per minute, giving the belt conveyer a speed of 23
_ feet a minute, using a 6-inch conveyer pulley.

ttt a ——— ee

94 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.
HoprPer SCALES.

A standard-type beam scale, with a sheet-iron hopper suspended, —
is used for weighing the potatoes as they come from the potato
washer. The hopper is 5 feet long by 3 feet wide by 2 feet deep,
which is large enough to weigh 20 bushels, or 1,000 pounds, of pota-
toes at a time. It is mounted on a pivot.

ELEVATOR.

From the hopper scales the sweet potatoes are dumped into a chute
which discharges them into the boot of a standard-type incline ele-
vator, equipped with a few variations to meet the needs in this par-
ticular case. The belt, which is 3 feet wide, is equipped with metal
buckets that form a sort of pocket in which the potatoes rest and are
carried to the top of the mash tank. Here the potatoes are dis-
charged into a chute which dumps them into the mash tank. The
elevator is 16 feet between pulley centers. The driving pulley makes
20 revolutions per minute, giving with 20-inch head pulley a belt
speed of 104 feet a minute.

MEASURING TANK.

After the sweet potatoes have been steam blanched water of the
same weight as the potatoes must be added before the mashing oper-
ation is started. To facilitate the measuring and handling of the
water, an elevated measuring tank is used. The tank is made of
24-cauge galvanized iron and is 4 feet in diameter and 6 feet deep,
with a capacity of approximately 4,600 pounds, or 550 gallons, of
water. <A 14-inch outlet quickly discharges the water from the meas-
uring tank into the mash tank. The tank can be readily filled by
means of a water pipe extending over the top of the tank. The num-
ber of pounds of water in the tank at any time may be determined by
a float arrangement attached to an indicator which runs on a cali-
brated scale. The tank is mounted on a platform high enough to
permit the water to be discharged into the mash tank by gravity.

CooLING TANKS,

In order to allow the crude sweet-potato sirup to stand for
approximately 40 hours and at the same time keep each batch sepa-
rate, two cooling tanks are required. These tanks are copper-jack-.
eted kettles, 3 feet 2 inches in maximum diameter and 5 feet deep,
with a capacity of 225 gallons each. The jackets of the tanks are
equipped with steam and water connections for heating or cooling
as desired. The sirup can be drawn from the tanks through a
14-inch outlet.

In order to keep the kieselguhr in suspension during filtration the
tanks are equipped with mechanical agitators, which really are
propellers mounted at the end of 14-inch shafts. Each contains three
8-inch blades and is driven by means of beveled gears and pinions.
The ratio of the pinions to the gears is 1 to 3. The pinions are driven
at 90 revolutions per minute, giving the propellers a speed of 30 revo-
lutions per minute. The kettles or tanks are mounted on steel stands.

fl f
|

t
e.

PRODUCTION OF SIRUP FROM SWEET POTATOES. 25
Mixine TANK.

It has been found desirable to mix the kieselguhr with water and

some crude sirup. before mixing it with all the crude sirup to be

filtered. For this purpose the mixing tank, rectangular in shape,

built of wood, and lined with galvanized iron, is used. This tank is

4 feet long by 3 feet wide by 14 feet deep and has a capacity of
approximately 125 gallons. The outlet is 14 inches. In order to
fill the tank with water a spigot connection extends over the top of
the tank, which is calibrated so that the quantity of water needed
can be determined accurately. r

Botcer.

The boiler for the proposed plant is an approved type of the return
tubular boiler. It has a capacity of 35 boiler horsepower. This

capacity was taken to give the most efficient operation for a plant of

this size and will take care of any peak loads in the plant. The floor

space required by the boiler is 8 by 15 feet. The boiler has standard

*% wrt con rs

equipment and is designed for 70 pounds gauge pressure operation.
The cost of the boiler complete is $500. The feed water pump will
cost $200, and $210 is allowed for the boiler setting.

ELEctTric Moror.

A standard type, 10-pole, polyphase alternating current electric
motor, with a rated horsepower of 5, furnishes the motive power for

the plant. The motor has a speed of 675 revolutions »er minute at

full load and runs at 110 volts. It weighs 550 pounds and requires
an over-all floor space of 2 feet by 184 inches. The value of the

- motor complete is.$150.

ToTAL Cost OF APPARATUS AND EQUIPMENT.

An itemized statement of the cost of all apparatus and equipment
necessary for the installation of the proposed plant for the manufac-
ture of sweet-potato sirup is given in Table 3.

TABLE 3.—Complete cost of installing plant capable of producing 100 gallons of
sirup per 10-hour day.

soo hci : 1 os ens
Equipment. Cost. Equipment. | Cost.

SS eee $170 || Pump (cooling tank to filter press) ......-- $200
SC a a a ee 300 || Pump (filter press to evaporator).......-.-- 67
EE eS eee eee eee 200 |} Pump (evaporator to flavoring Kettle)-.-..- 67
POR inS Sy es i ee ee eae Di5i|) Seales, tools; urucks, 6tG 6. 2b: . Soc. c a. 150
oe EE eee See 35 || Evaporator catch tanks (2)............-.-- 25
Ne eso rg CS ee an oe 350 || Filter-presscatch tank................-...- 10
meee tate LE eke. 75 || Benches and storage bins............-.----- 25
Se ee re 375 || Electric motor, 5-horsepower........-..--- 150
I S's ae a ee 15 |} Boiler, 35 boiler horsepower. --...--.------ 500
0 ES ee ee 700 || Boilerfeed water pump................-.-. 200
SES a ee Se ETA TB oA. LIS LR 11) 2 ge Alp er rr 210
UE Soo ee es CWE CUETO. pack, Sn A ee 150
OS Lak EE ae earl epee 206A) foabor im erechiOn.«._....-..---—.<..---.-.- 200
Memmeeteene Retcles-2 uo ee te Don | MEGS ae eee ne ek LOL 50
BemereeMACHING: . o_o. i once eke we She e's 208 SS he ee ee Se eee eee 150
Pump f ydraulic press to overhead tank)... 67 —
Pump (evaporator to cooling tank)........ 67 atl Senne ee TER ~ 745

26 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.
MATERIALS.

The same raw materials are used in the manufacture of the sweet-
potato sirup in the proposed plant as were used at the experimental
plant, namely, sweet potatoes, malt, and kieselguhr. At Fitzgerald
No. 1 Porto Rico potatoes were used. In the proposed plant the
sirup could be made from culls, the oversized and undersized sweet
potatoes, which cost only about 25 cents a bushel,?® thus greatly re- —
ducing one of the main cost items and, in turn, the total cost of pro- |
duction.

The malt and kieselguhr should be the same as those used at Fitz-
gerald (p. 15).

LABOR.

The following labor layout would be required:

One plant superintendent to supervise operations, handle plant cor-
respondence, look after pay roll, order raw materials as needed, keep
record of finished product, make shipments, etc.

One skilled laborer to take charge of plant operation, help with
the actual production of the sirup, keep apparatus and equipment in
first-class condition, keep plant records, ete.

Three laborers to help with the actual production of the sirup,
tend boiler fire, burn kieselguhr, ete. |

When it is desired to put the sirup into pint bottles, extra labor
is required. To put 100 gallons of sirup into pint bottles, per 10-
hour day, three extra men are required.

Since the proposed plant was considered as being located in one
of the southern States, the rate of pay prevailing in that section was
taken. A superintendent for a plant of this size would probably re-
ceive $1,800 a year. The skilled laborer to take charge of plant
operations could be secured for $3 a day, and the common laborer
could be secured for $1.50 a day. The higher wages which were paid
at the experimental plant were necessary because the employment
was temporary.

METHOD OF MANUFACTURE.

The method of manufacturing the sweet-potato sirup would be
the same as that at Fitzgerald (pp. 15-20). The method of handling
the materials, however, has been changed so as to eliminate some of
the labor requured at the Fitzgerald plant. This is especially true
in the handling of the sweet potatoes from the time they are taken
from storage and put in the mash tank for steam blanching.

In the proposed plant, the potatoes would be carried to the con-
veyer belt in the storage house and dumped on the belt which would
carry them to the washer. Immediately before the potatoes passed
into the washer, two men, one on each side of the belt, would give
the potatoes a visual inspection as they passed by. The potatoes
showing signs of rot, etc., would be picked off the belt and placed in
containers for disposal.

The potatoes would pass through the washer and drop on a chute,
which would convey them to the hopper scales. Here the potatoes
would be weighed, after which they would be dumped into a second

10 This was the consensus of opinion of sweet-potato growers around Fitzgerald.

- is 12.2 cents per gallon. The total manufacturing cost of the sirup

PRODUCTION OF SIRUP FROM SWEET POTATOES. 27

.
rea

chute. The hopper scales are designed to weigh 20 bushels of pota-
toes at a time. The second chute would conduct the potatoes to the
boot of an incline elevator. The elevator would raise the potatoes a
little above the top of the mash tank and discharge them into a
third chute, which would drop the potatoes in the mash tank. After
being leveled, the potatoes would be ready for steam blanching.
From this point on the material would be handled in practically the
same manner as at Fitzgerald, except in the matter of flavoring or
bottling the sirup. At Fitzgerald the sirup to be flavored or bottled
was drawn from the evaporator into 5-gallon cans and carried to
the flavoring and bottling kettle. In the proposed plant the sirup
would be drawn from the evaporator into the evaporator catch tank.
- From here it would be pumped as needed into the flavoring and
bottling kettle. The water to be added to the potatoes after steam
blanching would be measured in an elevated measuring tank, and
_ when wanted could be run directly into the mash tank, thus saving
time.

The modifications and improvements introduced in the process can
be noted by a comparison of the new flow sheet (Fig. 14) with that
for the experimental plant process (Fig. 11).

At Fitzgerald experiments were conducted on the drying of the
pomace secured from the pressing operation. This pomace was to

_be used as stock feed after drying. The excessively high cost of
drying the pomace, however, made this impractical. In the pro-
posed plant the pomace as it came from the pressing operation would
be placed in garbage cans and distributed among the consumers, a

_ method of disposing of the pomace without any expense.

= COST OF MANUFACTURE.

The complete cost of manufacturing sweet-potato sirup in a plant
of the proposed type, having a capacity of 100 gallons per 10-hour
_ day, has been calculated on the basis of the information secured at

Fitzgerald during the experimental runs of 1922. It was assumed

that culls would be used in making the sirup and that they would

cost 25 cents a bushel. The yield was assumed to be 1.37 gallons of
sirup per bushel of sweet potatoes, which was secured in 1922 at

Fitzgerald. Operating the plant for manufacturing the sirup in

conjunction with another plant would reduce some of the cost, such

as that for plant superintendent and office and miscellaneous ex-

penses. Also if a plant of greater capacity were built and operated,
_ the cost per gallon of the finished sirup would be less because of the
distribution of some of the fixed charges over a larger number of
gallons of the sirup.

The unit prices for the different cost factors are given in the cost
estimates. These prices will vary from time to time and with differ-
ent localities. Therefore it will be necessary for each manufacturer
to substitute the prevailing prices in his locality in order to secure
cost data adapted to his particular case. However, there should be
little difference between his cost figure per gallon and the one given
in this bulletin.

The cost of the containers when the sirup is put into 5-gallon cans

28 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.

WAGON
age Pine
POTATOES

STOCK OOM ORE HOUSE STOCK ROOM
MALT CULL SWEET AVESELGUHR
POTATOES
WASHER
CULL SWEET
POTATOES

SCALES SCALES SURNING

MALT CULL SWEET HIESELGUHR
POTATOES
MASH TANF

CULL SWELT
POTATOES
MALT

HYORAULIC STALLS
PRESS

POMACE
WORT

AIESELGUHR

STORAGE
7TANAC

WORT

\PORATOR MIX TANF

.
WORT HIESELGUHR
CAUOE S/RUP

COOL/NG AND
STORAGE TAN:

AIESELGUHR
FILTER PRESS STOCKH ROOM

CRUDE S1RUP
ATESELGUHR
STORAGE
7ANA
FILTERED
CRUDE SIRUP

PINT BOTTLE CASES

LABELS
COTTON SEED HULLS
CABBAGE bo ee FILTERED MAPLE FLAVOR
CANS CRUDE S/RUP GEORGIA CANE

FLAVOR/N S GALLON CANS JS/RUP
BOTTLING i
‘Pp

it
i
‘
|
,
|
1

N
%
S
S
S

hy
: : :
N
S
S
x

LABEL/NG

BOTTLED AND
CANNED S1RUP™

PACKING ae

FINISHED
FROOUCT
—_—— STORE HOUS.

Oi Bio eres eee eS ste eM yy i set!

PACKED SIRUP

SAIPMENT

PACKED S/RUP :

Fie. 14.—Flow diagram for proposed sweet-potato sirup plant.

——_—————

i tealearver se Secs mete dete

PRODUCTION OF SIRUP FROM SWEET POTATOES. 29
js 76.5 cents per gallon when put into 5-gallon cans. Thus the cost of
_ the containers forms 15.95 per cent of the total cost, which is rather
high. The total cost of manufacturing the plain sweet-potato sirup,
exclusive of containers, is 64.3 cents per galion. Table 4 gives the

estimated cost of manufacture per gallon for different kinds of sirup
_ when placed in various types of containers.

TaBLeE 4.—Estimated cost of manufacture per gallon of sweet-potato sirup of
different flavors in containers of different sizes.

Cost of—
Type of container. Artificial-
Plain | maple- oe
sirup. | flavored | “sii
sirup =
of TE Gin... Loe ee ee $0. 765 $0. 859 $0. 751
_ il EN 22 2.6 a a ee oe ee ee . 930 1. 024 916
LIP ERE cols vats Se ee a ee ee 948 1. 042 934
ST PED PAG. _. 5. chee eee ie ee ee ee 1.318 1,411 1, 299

The table shows the total cost of manufacturing the sirup, but

includes no cost for selling it. The profitable selling price would be

_ the total cost of manufacture plus the cost of selling plus the profit.

Tables 5, 6, 7, 8, and 9 show the itemized cost of the manufacture

of the various kinds of sirups when placed in the different types of
containers.

TABLE 5.—Cost of manufacturing sweet-potato sirup, exclusive of potatoes and

containers,
Cost.
.. |Artificial-| Cane-fla-
Plain |
: maple-fla- vored
Cost items. over vored | sweet-
ate sweet- | potato
(100 Pi. | potato | sirup
8a sirup (100 (111 gal-
lons)
| gallons).| lons).
malt (7.4 pounds at $4.50 per 100 pounds)... ..:.-.......-.-.2-2-.---2---- $0. 33 $0. 33 $0. 33
Kieselguhr (73 pounds at $4.07 per 100 pounds)................-...-.-.---- 2. 98 2. 98 2. 98
Labor (3 men at $1.50 per day and 1 man at $3 per day).............-...-. 7. 50 7. 50 7.50
flant superintendent ($1,800 per year). -...... 2.2... 2... 222-220. eecee sees [= Se 9. 38 9.38
a BE TS Ste DE a ee 5. 30 5. 30 5.30
Rape (et ew ai it wa per Kw. hr.)-5.. 22. 02 A ciel livesclolecle:. <307-] . 30 . 30
Electric power (28 kw. hr. at $0.10 per kw. hr.).....................-.---. 2. 80 2. 80 2. 80
Water (7,000 gallons at $0.25 per 1,000 galloms) --..................-...---. 1.75 155 IY
Interest on investment (6 per cent of $15,145= $908.70 per year). .-........ 4.73 4.73 4.7;
Depreciation on buildings (4 per cent of $8,400=$336 per year) .-........-. ere 175 PS
Insurance on buildings (4 per cent of $8,400=$336 per year) .........-.-.... 1.75 1.75 1.75
Depreciation on equipment (8 per cent of $5,745=$459.60 per year)........ 2. 40 2. 40 2. 40
Insurance on equipment (4 per cent of $5,745= $229.80 per year) .........-- 1. 20 1, 20 1.20
Taxes (1 ed SETAC EC EES a ee ee eft TEM .49 .49 | .49
eee eG AINISCOUANPONS EXpenses: © s. 02.2. ol 2 ke field ce see ods eee. 2. 00 2. 00 2. 00
Hauling (6.5 miles at $0.10 per mile) ................ Be led ek Oe ae . 65 . 65 . 65
Artificial maple flavor (100 ounces at $0.0938 pe OUCe) Heo eS eee eee O:38iules 2 ee
Georgia cane sirup (11 gallons at $0.50 per gallon) .......................-.|.-.-..-.--|---- ce 5. 50
MOLATCOSG: —. 22-52 ok aE aS Pe ee ene eee SF SAE Ede y | 45.31 54. 69 50. 81
ELECTS Ey Pai Da reas gE to ee 453 547 . 458

u1Jn figuring the cost of manufacture, an item ‘ Interest on investment’ which in-
sures a reasonable return on the money invested, is allowed.

30 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.

Cost of manufacturing sweet-potato sirup, including potatoes, exclusive —
of containers,

TABLE 6.

Artificial-

Plain j|maple-fla- Cane-fla-
; sweet- vored wi t
Cost items. potato | swee cee

i tato
sirup (100} potato |_.P°
gallons). \sirup (100/S!7UP (ill

gallons). gallons).
Cost of manufacturing sweet-potato sirup, exclusive of potatoes and con-

PATI ONS 2s ost ie eats eee ee pe cere eh ee ge $45. 31, $54. 69 $50. 81
Potatoes (73: bushelsijat7s0!25 per bushel) ses = ee eee a eee 18. 25 18. 25 18. 25
Shrinkage (4 per cent) (3 bushels at $0.25 per bushel)....................- «15 Sg, Be (5

ROLACOSts mice wee See a eet oe eee ee ee Oa ee ee 64. 31 73.69 69.81
Cost pergallonm..'.2. sis ee es eee 643 137 - 629

TABLE 7.—Cost of manufacturing sweet-potato sirup in 5-gallon cans.

Artificial-
Plain |/maple-fla- pein
sweet- vored ee
Cost items. potato sweet- at dees
sirup (100] potato wee ate
gallons). |sirup (100 alto )
5 gallons). Saas):
Cost of manufacturing sweet-potato sirup, exclusive of containers. ......-. $64. 31 $73. 69 $69. 81
20)s-fallon' cans ati$0.6 hieachs: ha: ase. sess tee ae ees ee ee eee 12. 20 12:20:73, |o3 eee
22.2'5-galion cans at $0.61 each. ... << o scn a ee Lo ccs no aan nek «eee eee eee 13. 54
PObAl COSt ses oho doce 5 eee Veemwcistas & Xo See 76. 51 85. 89 83. 35
Wosbper Palle: 2” acca. ore atc one eet oes Pe eee eee . 765 . 859 oiol

TABLE 8.—Cost of manufacturing sweet-potato sirup in 1-gallon cans.

Artificial-
Plain |maple-fla- ctv
sweet- vored wast
Cost items. potato sweet- otato
sirup (100) potato sirup (111
gallons). |sirup (100 alanis}
gallons). | &
Cost of manufacturing sweet-potato sirup, exclusive of containers. ........ $64. 31 $73.69 $69. 81
100.1-eallion: cans at'$0:22 perican’. .. 3.2. So--- . se eee ee ere 22. 00 22.00 |= 2 eee
16:67 (cases at; $0.40: per Cases: 22. Aes Se eee cae to ee eee 6.67 6.67 |s225-Seeee
111 1-gallon cans at'$0: 22 per.cam. = 628, oo sche cob ak ee se epee ee necks Coe eee ee ee ee eee 24. 42
18:5\cases.at $0.40 perease: 244. 22. hese eeek See eS eet ae enee ee OR EE nr ee eR 7.40
Total CoSt: 22cs..2 Seen ere a ee or Ee 92. 98 102. 36 101.63 —
GCostiper pallon. 222.20 <, ste Sate cote eee eee eee . 930 1. 024 . 916
TABLE 9.—COst of manufacturing sweet-potato sirup in 1-quart cans.
Artificial-
Plain |maple-fla- eee
sweet- vored awe
Cost items. potato sweet- olako
sirup (100) potato Be fate
gallons). |sirup (100 alae}
gallons). | ® 3
Cost of manufacturing sweet-potato sirup, exclusive of containers. ........ $64. 31 $73. 69 $69. 81
400 Quart.cans:at06 per lOO. coe. cc ccicicn nas nosbacsetheeemec eee oee eee 24. 00 24. 00! / \oareme eee
Ize cases ab $0.52 Per CAS@s. =... 25 Fe sade a woes ee eee ee oe eee Ieee EE 6.50 6.50" | secee
444 quart cans at $6 per 100.......-. ee rr rater Pgh oe | has eal sa etes 26. 64
13:88 cases'at $0:52 per'case:. <2... fag. 8a cei soo sk acess eee eae ee eee See ee eee ees 7. 22
otal COSt:...<. .< J22 bo 55 th ew dee dee oe ae ee eee 94.81 104, 19 103. 67
Oost per gpallon;:: 28.06. ose fone hee sone caee eet Le Cee . 948 1, 042 - 934

PRODUCTION OF SIRUP FROM SWEET POTATOES. 31

TasBLe 10.—Cost of manufacturing sweet-potato sirup in 1-pint bottles.

| artificial.

Plain |maple-fla-| Cane-fla-
sweet- vyored | | oweck-
Cost items. pete sweet- | ara
p (100) potato sirup (111
ee sirup (100 aHieata)
deribe, asain gallons). Wy
Tne Pere
_ Cost of manufacturing sweet-potato sirup, exclusive of containers-.....-... | $64.31 $73.69 $69.81
) Additional labor (3 men at $1.50 per day)............-..------------------| 4.50 | 4.50 } 4.50
maeoo pint bottles at $4.17 per 100...........---....-.------------------------ | 33.36 = Ee ee ee
eee 2.80 7 ae (See
0 SEED TL By Se ee eee 2.08 2.059 [2 22-22 ee
EE Sahel CTT pal | ee ee ee ee 1.32 #32 [ete
ES SCE TES ee ae Ee ee fey Go eae ded i
” 3.4sacks of cottonseed hulls at $0.80 per sack.............--.-------------- 2.72 | y Ty ay ee ES
_ 888 pint bottles tig 17 oper Te a eR se ea Se ee eee an pee te! 37.03
> Beer anetes ak 25 pe Fa. = Soe ee ee a ee ee eae Se 3-11
ee eee ee SE EE 2S oe 5 ee ee = ie ay Pe eee PAS ee 7S
888 labels at $0. _ SEL Sti Se eee Pa eee oe | 1.47
0 LEEPER DLS i ETE Sie es ee ee ee een en Se pe Se oe 22.94
| 3.77 sacks of cottonseed hulls at $0.80 per sack...217 122277222222. Slee feast Fi | 3.02
a TU OD Bad A eR Se | 131.76 | 141.14 144.19
4 eae et aie poe es Sa lee | 1.318 1.411 | 1.299
> J
= PRECAUTIONS TO BE OBSERVED.

Although the method used in making sirup from sweet potatoes
_ is simple, the following precautions must be taken to insure the pro-
_ duction of sirup of fine quality:
_ Use pale distillers’ malt in the proportion of from one-tenth to
_ one-fifth of 1 per cent of the potatoes taken.”
_ Use washed potatoes, free from decay.
> Use kieselguhr as a filter aid.’
: In cooking, reject the condensed water flowing from the mashing
tanks.
Use no wooden equipment in the pores of which potato juice has
- been allowed to decay.**
Clean equipment often enough to avoid all danger of spoilage.
Arrange equipment so that it can be cleaned readily.
Once the operations are started, complete the process without
delay.
: aeant letting the sirup thicken or bake on the evaporator ** coils.

2 Investigation of the action of the malt showed that to avoid the strong flavors
which some kinds of malt impart it was desirable to use a light-colored distillers’ malt
and to reduce the malt requirement to a minimum. The quantity of commercial pale
distillers’ malt required was only from one-tenth to one-fifth of 1 per cent of the weight
of the potatoes. The principal reason for this very small requirement was that the
sweet potato has a very active diastase which digests a large proportion of the starch
while the potatoes are being heated.

# The laboratory results indicate that in filtering the kieselguhr (diatomaceous earth),
“5 as a filter aid, should be ignited at a low red heat as recommended by Caldwell
(U. S. Dept. Agr. Bul. 1025) as a satisfactory method for eliminating the peculiar flavor

. which the untreated material seems to impart to the sirup. The kieselguhr, if reignited
between each use, could be used repeatedly.

14 The laboratory work also showed the necessity of taking care that the hot wort or
sirup never comes in contact with the wooden surfaces of racks, pressure platform, or
other equipment, in the pores of which potato juice has been allowed to decay, as such
contact is likely to cause contamination in flavor.

145 The laboratory work showed that color and flavor were injured by allowing the sirup
to bake on steam-heated surfaces, this work leading to better evaporating practice.

Pay ee Tee eT Mar PS

J .
:
P
F
|

32 BULLETIN 1158, U. S. DEPARTMENT OF AGRICULTURE.

To produce clear sirup, evaporate crude sirup to 60° Brix or above,
let it cool and stand for about 40 hours, then dilute it to 45° Brix
with cold water containing kieselguhr, filter, and reevaporate.1®

GENERAL PROPERTIES OF SWEET-POTATO SIRUP.

Sweet-potato sirup is clear and has an amber color. The taste is
sweet, with a slight distinctive flavor and a slight after taste. It
is not as sweet as cane sirup, honey, etc., which are characterized by
high proportions of sucrose or invert sugar.

COMPOSITION OF SWEET-POTATO SIRUP.

The analysis of a sample of the sirup made at Fitzgerald is given
in Table 11.

TABLE 11.—Chemical composition of sweet-potato sirup.

7a ine rt ee
etermination. z ree
analyzed. aie
Sohds (hy specific gravity) (per ednt)_iis-2e este es ee eee 62.50! | 244 S52-
a CER GEHL) - <5 25.2 stank ea ae Smes ain Se eee oe eg ee eee ae ae ee ee 1.02 1.63
IPTOLetn CN 20 6:25) (percent) eee. os ee Cee ea ee ee ene 1.03 1.65
Direct: polarization (°V..):23) 3.2 Se fe eo Pea eee ee a eee |}; 10454 hv = Saeees
In Vere POlArWwaAliOn: (LV Jian eee Se ee | eat eee 9252: tee ee
reduce Suzaras invert (percent)! jis: eee ea ee eee 2h | See
Reducing sugar. as maltose (percent) 2-08 sae ee eee ee ee 36. 23 57.94
Motalsupar assnyerb-Cper. Cent) 2235 8a2 ae ee ee eee oe ee ee ee = oe ae 31556 ee cae
Sucrose by polarization (percent). -..22 35 es en ee ee ee cree 9.40 14.96
Sucrose by reduction (percent) &. 55s 22 eae ee ae eee ee eee ae ee 9.30 14.96
Dextrini(per.cCent)' 8: cone ashes Ses (Se ee a ee ee 12.47 19.95

1 Analysis made in the nitrogen laboratory of the Bureau of Chemistry.

2 Munson and Walker method. The cuprous oxid on ignition gave over 98.5 per cent of cupric oxid,
showing that it was nearly pure. ;
Ee, fermentation method described in J. Assoc. Official Agr. Chemists, Methods of Analysis (1916),

p. 179.

Sweet potatoes contain very little dextrose or levulose, and practi-
cally no inversion of the sucrose present occurs during sirup making.
For these reasons a much better idea of the composition of the sirup
is given by the application of the usual methods of analysis than
would otherwise be the case. Thus, this analysis shows that the car-
bohydrates of the sirup are mostly maltose (57.94 per cent of the
sirup solids), dextrin (19.95 per cent of the sirup solids), and
sucrose (14.96 per cent of the sirup solids).

COMPOSITION OF SWEET-POTATO POMACE.

The chemical analysis of the dried sweet-potato pomace, deter-
mined by the cattle-food laboratory of the Bureau of Chemistry, is
given in Table 12.

16 One of the most difficult problems was the development of a simple method whereby
a sirup which would be clear and would remain so on cooling and standing could be
produced. The substance which gave most difficulty was a salt of unknown composition
which separated out in minute quantities in the finished filtered sirup, thus rendering it
turbid. This difficulty could be overcome by concentrating the wort to about 60° Brix
and letting it cool and stand for at least 40 hours. During this time enough of the salt
separates in the sirup so that by diluting it with cold water to about 45° Brix, filtering,
and reevaporating to final density the sirup will remain clear on cooling and standing.

PRODUCTION OF SIRUP FROM SWEET POTATOES. ae

TasLe 12.—Chemical composition of dried sweet-potato pomace.

Determination. Per cent. Determination. Per cent.

LS 50D. ee SSeS eee eee ANSOE | MELOvCINpertnter a. chee cast Peete oe 23.06
Dl. .cs. 42 23 Bees as 3 ee ee ere a A AGe | ROT e fier sa. St ct oa cok Ba Ack ane ees 13.50
DEPMIIO SUT C Ue ie ao. ncn ccs Coe cine ec cuhs 30) Nitrogen=free extract)... .<--2-....2502..- 50.09

This analysis indicates the probable high feed value of this pomace.

SUMMARY.

A method for the commercial manufacture of sweet-potato sirup,
based on laboratory and plant experimental work, has been developed
by the Bureau of Chemistry. The following important points were
brought out in the course of this work:
| Conversion of starch is accomplished satisfactorily by using malt
equivalent to one-fifth of 1 per cent of the weight of the potatoes,
by maintaining a temperature of 140° F., and by allowing the sirup
to stand for 45 minutes after the addition of the malt.
_ The drying of the pomace proved to be uneconomical, although it
may have a high value as a feed.
he use of the atmospheric or open-kettle evaporator was prac-
ticable in concentrating the crude and filtered sirups.
To produce a permanently clear sirup it was practicable to let the
_ crude sirup cool and stand for 40 hours and then filter it, in order to
remove certain salts which caused turbidity.
Satisfactory results were obtained in the filtration of the sirup by
using ignited kieselguhr as a filtering aid, 2 per cent of the weight of
_ the potatoes being employed, and filtering cold at 45° Brix.
| The yield obtained varied. During the spring of 1921 it was 1.55
_ gallons of sirup to a 50-pound bushel of potatoes. An average yield
of 1.87 gallons of sirup to a 50-pound bushel of potatoes was obtained
_ during the spring of 1922.
Adding 10 per cent of other sirups with a sucrose or invert sugar
/ content increased the sweetness of the experimental sirup.
. From the standpoint of quality the sweet-potato sirup has possi-
_ bilities for use as a table sirup, for cooking purposes, and in the
manufacture of colored and short-grain candies, such as taffy, kisses,
and caramels. For baking purposes it might find use in dark
products, such as ginger snaps. It also has properties suitable for use
in blending with other sirups to prevent crystallization.

For the proposed plant of 100 gallons per day capacity the cost of
manufacture of plain sweet-potato sirup, exclusive of containers, is
estimated to be 64.3 cents per gallon.

The commercial possibilities of sweet-potato sirup are limited by
_ the high cost of manufacture under the present method.

ORGANIZATION OF THE U. S. DEPARTMENT OF AGRICULTURE.

Secretary of Agriculture 3. 28). i ss HENRY C. WALLACE.
Assraiant Secretary: -- 2-2". ee C. W. PUGSLEY.
Ahrecto? of Scientific Werk —- 22k Ses HD. BACK.
Director of Regulatory Work
Weather Buréauls as Sesh ee CHARLES F. Marvin, Chief.
Bureau of Agricultural Economics_______- Henry C. TAytor, Chief.
Bureau of Animal Industry_____-____-~_- JOHN R. MouHter, Chief.
Bureau of Plant Industry. —_2 = See WittiAmM A. Taytor, Chief.
POPES. SCTUICE: 2 4! a ie ae W. B. GREELEY, Chief.
Bureaw of Chemistry. =22 5 Sis ee ee WALTER G. CAMPBELL, Acting Chief.
Puree of Sotts 2 Fe eh eee MILTON WHITNEY, Chief.
Bureau of Entomology__.-—--— = L. O. Howarp, Chief.
Bureau of Biological Survey___-___-~--__- E. W. NELson, Chief.
| Bureau of Public Roads___________-______ Tuomas H. MacDonat.p, Chief.
| Fixed Nitrogen Research Laboratory_____ F. G. Corrre.y, Director.
F| Division of Accounts and Disbursements_. A. ZAPPONE, Chief.
4 Dinsion of Publications__2_- —* Epwin C. PowELL, Acting Chief.
} DT Gig nd Et SU ee Pe eet CLARIBEL R. BARNETT, Librarian.
Sidtes Relations -Servicej__.~ = 2 ss A. C. TruE, Director.
Federal Horticultural Board____________~ C. L. Maruatr, Chairman.
Insecticide and Fungicide Board_____~ —___. J. K. Haywoop, Chairman.

Packers and Stockyards Administration__| CHESTER MorRIL1, Assistant to the
Grain Future Trading Act Administration__| Secretary.
Onice ofthe Solicitor 222228 2) te bass R. W. WiLiiAMs, Solicitor.

This bulletin is a contribution from—

Bureau of Chemistryc_ sy 23 fe ee WALTER G. CAMPBELL, Acting Chief.
Fruit and Vegetable Utilization Lab-
OTOLOT Ys oi. = 3: ee eR are en Be H. C. Gore, in charge.
Office of Development Work_____- D. J. PRICE, in charge.
34

ADDITIONAL COPIES
OF THIS PUBLICATION MAY BE PROCURED FROM
THE SUPERINTENDENT OF DOCUMENTS
GOVERNMENT PRINTING OFFICE
WASHINGTON, D. C.
AT

10 CENTS PER COPY

PURCHASER AGREES NOT TO RESELL OR DISTRIBUTE THIS
COPY-FOR PROFIT.—PUB. RES. 57, APPROVED MAY Il, 1922

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