UNIVERSITY OF CALIFORNIA

COLLEGE OF AGRICULTURE

AGRICULTURAL EXPERIMENT STATION

BERKELEY, CALIFORNIA

THE PRINCIPLES AND PRACTICE
OF SUN-DRYING FRUIT

BY
A. W. CHRISTIE AND L. C. BARNARD

BULLETIN No. 388

May, 1925

UNIVERSITY OF CALIFORNIA PRINTING OFFICE

BERKELEY, CALIFORNIA

1925

Digitized by the Internet Archive

in 2012 with funding from

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THE PRINCIPLES AND PRACTICE OF
SUN-DRYING FRUIT

By A. W. CHRISTIE and L. C. BARNARD

EXTENT OP THE DRIED FRUIT INDUSTRY

From the beginning of fruit growing in California, sun-drying
has been one of the principal methods of preserving fruit for market-
ing. While sometimes used as a means of preserving fruit which could
not be marketed through other channels such as fresh sale or canning,
sun-drying is a primary industry, as evidenced by the large proportion
of fruits grown expressly for drying. The quality and world-wide
distribution of her dried fruits have made California the leader of
the world in this field. In fact, the dried fruits of California are
considered the standard of excellence.

Various causes have contributed to the development of sun-drying
in California, the most important being its sub-tropical climate. The
long, warm, dry summer is not only favorable to the production of the
principal drying fruits, but since the ripening of most of these fruits
normally occurs in dry weather, it is possible to utilize this simple,
natural method of food preservation. Because California is situated
several thousands miles from her principal markets, dried fruits repre-
sent the most economical form in which the crops can be transported
and offered for sale. Although cooperative canneries are growing,
drying is in general the principal method by which the individual
grower can preserve his crop in a durable form. The great increase
in the production of dried fruits in recent years has been largely due
to the activities of the several cooperative marketing associations.
These associations have enabled the growers to retain control of their
dried products through all the stages of packing and distribution to
the ultimate consumer and by means of standardization, attractive
packaging and advertisement to very greatly increase the demand for
California dried fruits.

According to the 1919 census, California produced 94 per cent of
all the dried fruits of the United States. With the exception of prunes
in the Pacific Northwest and evaporated apples in several states, Cali-

4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

fornia enjoys a practical monopoly in the production of nearly all
kinds of dried fruits. The extent of the industry can be seen by
reference to Table 1, which gives the tonnage produced in 1923 with
a conservative estimate of their value to the producer. Table 2,
gives the total acreages of certain fruits for 1924. It is difficult to
estimate what proportion of these acreages were devoted to the pro-
duction of dried fruits. In most cases, the proportion of the total
crop which is dried varies considerably from year to year according
to changes in the market for fresh and canned fruits. From 30 to 40
per cent of the peach and apricot crops are dried normally and of pears
usually not over 10 per cent. Over 90 per cent of the figs and raisin
grapes are dried and the quantity of prunes not dried is negligible.

TABLE 1

Tonnage and Value of Sun-Dried Fruits for 1923

Dry tons*

Estimated farm value

Per pound

Total

Apricots

30,000

9,500

26,000

2,000

131,000

280,000

20c

7c

10c

10c

7c

4c

$12,000,000

Figs

1,330,000

Peaches

5,200,000

Pears

400,000

Prunes

18,340,000

Raisins

22,400,000

Total

478,500

$59,670,000

Compiled by Dried Fruit Association of California.

TABLE 2
Acreages of Certain Fruits in

L924*

Bearing

Non-bearing

Total

Apricots

68,887

23,982

120,947

45,407

138,558

297,164

21,022
24,269
28,455
24,593
47,261
60,291

89,909

Figs

48,251

Peaches

149,402

Pears

71,000

Prunes

185,819

Raisin Grapes

357,455

1924.

Compiled by E. E. Kaufman, Calif. Coop. Crop Reporting Service. Includes acreages planted in

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

From the large-non-bearing acreages given in Table 2, to which
should be added extensive plantings made in 1925, it is evident
that the production of dried fruits must inevitably increase. If
fresh shipment and canning do not keep pace with the increasing
production, it may become necessary to dry a greater proportion of
the fruit crop than formerly. The production of dried fruits is also
expanding in other parts of the world, notably Australia and South
Africa. At present, the rate of financial exchange and other condi-
tions resulting from the world war seriously restrict exports of dried
fruits from the United States and moreover permit the importation of
certain dried fruits from the Mediterranean countries. The amount
of dried fruit exports and imports in 1923 can be seen from Table 3.

TABLE 3

United States Imports and Exports of Sun-Dried Fruits
(Fiscal Year 1922-23)

Tons imported

Tons exported

Apricots

0

18,293

0

0

6,168

9,462

5,597

Figs

0

Peaches

2,793

Prunes ....

39,615

Raisins

46,981

Currants

0

Total

33,923

94,986

From U. S. D. A. Year Book, 1923.

PBINCJPAL LOCALITIES AND VAEIETIES FOE SUN-DEYING

With the exception of the extreme northern part of the state and
the mountainous districts of the Coast Range and the Sierra Nevada,
fruits are grown and dried in almost every agricultural region of
California. Some districts have been found to be particularly suited
to the growing of certain kinds of fruit and have consequently taken
the lead in the production of these fruits. Likewise certain varieties
because of higher quality or yield have been most extensively planted
and dried and have, therefore, become the trade standard. The follow-
ing paragraphs give briefly for each fruit the principal counties and
varieties, the usual drying season, and the average drying ratios and
yields.

b UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

Apricots. — The counties producing dried apricots are, in order of
importance : Santa Clara, Ventura, Riverside, Los Angeles and San
Benito. The Sacramento, San Joaquin and Pajaro valleys also con-
tribute large quantities. The principal varieties dried are, in order of
importance: Royal, Blenheim, Tilton and Moorpark. To be suitable
for drying, an apricot should be of fair size and rich flavor and have
a uniform golden color. In the interior valleys, the drying season
begins between June 15 and July 1, while in the coast counties picking
rarely begins until July 1 to 5. The acre yield varies from 3 to 9
fresh tons, averaging between 5 and 6. The drying ratio will vary
from as low as 4 :1 for very large ripe fruit to as high as 7 :1 for small
early maturing fruit, and averages about 5:1. The normal yield of
dried fruit is from 1 to 1% tons per acre. For further information see
Circular 238 of this station — "The Apricot in California."

Peaches. — Peach drying is most largely practiced in the Sacramento
and San Joaquin valleys. Some peaches are dried in southern Cali-
fornia but few along the coast or in the foothills. The leading counties
in order of importance are : Fresno, Tulare, Placer, San Bernardino
and Solano. Only firm yellow freestone varieties, principally the
Muir, Lovell and Elberta, are dried commercially. In the San Joaquin
Valley peach drying begins as early as July 15 for Muirs and con-
tinues into September for Lovells. In the Sacramento Valley most of
the peaches are dried during August. The acre yield may vary from '
5 to 20 fresh tons, and averages not over 10 tons. The drying ratio of
Muir and Lovell varies from 4 :1 to 5 :1, while the Elberta will shrink
from 6 :1 to 7 :1. A general average drying ratio would be about 5 :1.
The average yield of dried peaches is about 1% tons per acre.

Pears. — Bartlett pears, the only variety dried, are grown princi-
pally in Sacramento, Solano, Los Angeles, Santa Clara, San Luis
Obispo, Yuba and Lake counties. Except in Lake County only pears
unsuited to fresh shipment or canning are usually dried. Ordinarily
windfall pears, bruised or blemished but otherwise sound are used
for drying, but in Lake County a large proportion of the whole crop
is dried, which makes this county the leader in quality as well as in
quantity of dried pears. In the Sacramento Valley and foothills dry-
ing begins about July 15 and extends throughout August, while in the
north coast counties it begins during the latter half of August and
extends through September. Pears yield from 10 to 20 tons per acre
but because of the fact that in most localities only a varying portion
of the crop is dried no exact figures for the acre yield of dried fruit
can be given. The drying ratio varies from as low as 4:1 in Lake

Bull. 388] PRINCIPLES OF SUN-DRYING FRUIT 7

County to as high as 7 :1 in the Sacramento Valley, averaging for the
state about 5 :1.

Primes. — The greatest prune acreage is to be found in the valleys
near the coast, such as those of Santa Clara, Sonoma, Napa and San
Benito counties. The acreage in the Sacramento and San Joaquin
valleys is rapidly increasing — Tulare, Solano and Butte being leading
counties. The most important variety is the French prune. Other
important varieties are : Imperial, the largest variety and grown prin-
cipally in the northern coast counties; Sugar, not so high in quality
as the French, but a heavy bearer in the interior valleys; Robe de
Sargeant, similar to the French. In the warmer sections, drying begins
during the latter part of August and extends through September, but
where the prunes are late in maturing drying may commence in Sep-
tember and extend well into October. A prune orchard will produce
from 3 to 10 tons of fresh prunes per acre. In the coast counties the
drying ratio ranges from 2 :1 to 2% :1 and in the interior valleys and
southern California from 2% :1 to 3 :1, the state average being nearly
2a/2 :1- The average acre yield of dry prunes is two tons. For further
information see Bulletin 328 of this station, "Prune Growing in
California. ' '

Figs. — Most of the dried figs are produced in the San Joaquin
Valley, the leading counties being Fresno, Tulare, Merced, Stanislaus
and Madera. Some figs are dried in the Sacramento Valley, especially
Mission figs in Yolo County. The most important variety is the white
Adriatic, which is used exclusively for drying. The next in import-
ance is the Calimyrna, which is being extensively shipped and canned
as well as dried. The third variety is the Black Mission, the first crop
of which is shipped fresh and the second crop dried. The Kadota is
used primarily for preserving, but if caprified produces a fair dried
product. Figs, especially those which produce two crops, ripen over
a long season. The figs drop to the ground when high in sugar and
already partially dried and the harvesting season extends from late
July to the beginning of cold wet weather in October or even November.
Calimyrna orchards produce from 1 to 2 tons and Adriatic and Mission
varieties 2 to 4 tons of dried figs per acre, the average for the Cali-
myrna being 1.2 and for the other varieties 2.5 tons per acre. The
drying ratio of figs as normally harvested for drying is lower than
that of any other fruit, rarely exceeding 1% :1. However, figs picked
for fresh shipment or canning would have a drying ratio of about 3 :1.

Raisins. — Over half the grapes grown in California are of raisin
varieties, 95 per cent being produced in the San Joaquin Valley.

8 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

Fresno County, which produces half the world's supply of raisins,
omitting currants, is first, followed by Tulare, Kings, Madera and
Merced counties. Sutter, Yolo and Yuba counties produce notable
quantities of seedless raisins and small quantities are produced in
southern California. The varieties used for raisins are, in order of
importance: Sultanina (Thompson Seedless), Muscat, and Sultana.
Wine and table varieties are dried to some extent, but are generally
referred to as dried grapes rather than as raisins. The raisin season
extends throughout September and October, according to the time of
maturity for a particular variety or district. Good vineyards yield
from 5 to 15 tons of grapes per acre. The drying ratio is regulated
by the sugar content and may vary from 3:1 to 4:1, averaging 3% :1.
The average yield of raisins is from % to 1% tons per acre, although
many vineyards produce as high as 2% to 3 tons.

PKINCIPLES OF SUN-DKYING FEUIT

The methods and equipment used in sun-drying fruit are still very
much the same as those adopted in the beginning of the industry. Very
little scientific study has been given the principles and practices and
little exact information has been published. The demand for such
information is growing greater and more insistent. Many persons
without previous experience are engaging in the growing and drying
of fruits and even experienced growers are realizing more than
formerly that a thorough understanding of the principles of drying
coupled with knowledge of the most successful methods and equip-
ment are essential to the economical production of dried fruits of
quality.

If the production of dried fruits in California is to be profitably
maintained in spite of constantly increasing production, both domestic
and foreign, it is imperative that the quality of our products be of
the highest. The individual grower is the most important link in the
chain which produces and markets dried fruits and unless he gives the
same care to the production of his dried fruit as to the food on his
own table, he will not obtain the sale value his product should have.
The principles and practices are simple and readily grasped but must
be understood and followed in order to get the best results.

Legend for color plate:

Fig. 1. — Types of sun dried fruits (actual size of grades)

1. Muir Peach (Extra Fancy) 4. Bartlett Pear (Choice)

2. French Prune (50/60) 5. Adriatic Fig (Extra Fancy)

3. Eoyal Apricot (Choice) 6. Calimyrna Fig (Extra Fancy)

BULL. 388] PRINCIPLES OF SUN-DRYING FRUIT 9

The writers have supplemented several years of experience in fruit
drying by an extensive survey of dry -yards in all sections of the state.
Many differences in methods and equipment were noted, some caused
by well defined climatic or other conditions while the reasons for other
differences were uncertain. The following pages present what may
be termed ' ' Standard Methods of Sun-drying Fruits. ' ' It is not to be
expected that these directions will fit exactly each individual case but
it is hoped that they will serve as a general guide for all growers who
desire to dry their fruits in the most efficient manner.

EELATION OF CULTUEAL PRACTICES TO QUALITY OF DEIED FEUITS

The quality of dried fruits does not depend alone on the treatment
after picking but reflects the management of the orchard or vineyard
throughout the year. Conscientious application of the best cultural
practices of cultivation, irrigation, fertilization, pruning, etc., is essen-
tial to the production of clean fruit of large size and good quality.
Proper spraying is often necessary to obtain fruit free from defects
due to disease or insect attack. Dried fruit of the larger sizes and
fine quality is always in demand at good prices while dried fruit of
poor quality and small size is generally difficult to dispose of even at
much lower prices. It is important, therefore, that each and every
grower exert all reasonable effort toward the production of the best
quality, not only for his personal profit, but in order that the markets
for California dried fruits may be strengthened and maintained.

Thinning to increase size is a very important operation with
apricots and peaches. Small fruit is more expensive to handle, shrinks
more in drying and brings a lower price. The following figures
furnished by the California Peach and Fig Growers' Association, indi-
cate the financial advantages of thinning. Thirteen peaches (twenty-
six halves) make one pound of extra fancy dried peaches bringing 17
cents per pound while fifty-four peaches (one hundred and eight
halves) are required to make one pound of standard dried peaches
bringing only 10 cents per pound. The small peaches contain 7 to 9
per cent of pits while the large peaches lose only 5 per cent in
pitting. To produce one pound of dried peaches of standard grade
necessitates the picking, cutting and drying of four times as many
peaches as are required to produce one pound of extra fancy dried
peaches. The cost of cutting "Standards" is about 94 c per dry pound
as compared to %c per dry pound of ' ' Extra Fancy, ' ' and the picking
cost for small peaches is half again as great as for large. The smaller
sizes, are therefore, more expensive to produce and the price obtained
is much lower.

10

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

Comparative observation on the effects of thinning apricots, by
Farm Advisor C. C. Staunton of Ventura County in 1923, showed a
value for the dried apricots resulting from each box of fresh fruit
from the thinned plots of $1.22 as compared with 79 cents for the
dried fruit from adjacent unthinned plots. This gain of over 50 per
cent in value was principally due to the higher prices received for
the larger sizes. The unthinned fruit consisted entirely of Standards
(the smallest size-grade). The methods of thinning deciduous fruits
are described in Circular 258 of this station.

EIPENESS OF FKUIT AND METHODS OF PICKING

Fruit intended for drying should be thoroughly matured. With
the exception of pears, no fruit should be picked for drying until it
has developed its full ripe color and flavor and has reached its maxi-
mum sugar content. When in prime condition for eating, fruit is also
in prime condition for drying but not before.

The hard partially green fruit required for commercial canning
or fresh shipment is entirely unsuitable for drying. Such fruit, when
dried, yields a product of low grade, lacking in color and flavor,
excessively shrivelled and curled up and, because of its deficiency in
sugar, always gives a lower yield of dried product. The effect of
maturity on the drying ratio of peaches and apricots is illustrated in
Table 4. In each case the fruit was picked at one time from a small
group of trees at the University Farm, graded for maturity and all
lots reduced to the same degree of dryness.

TABLE 4

Effect of Maturity on the Drying Eatio of Peaches and Apricots

Condition

Blenheim

apricots.

Drying ratio

Muir peaches

Drying ratio

Per cent of sugar

Soft ripe

Firm ripe

Hard ripe to green

4.16:1
4.50:1
6.40:1

4.86:1
4.64:1
5.11:1

48.5
48.5
45.0

Over-ripeness in fruits that require cutting is also to be avoided
because very soft fruit is difficult to cut and dry without losing its
shape and forms dark colored "slabs" which stick tight to the trays
and bring a low price.

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

11

Pears do not ripen satisfactorily on the tree and they are, there-
fore, always picked green and allowed to ripen in boxes or bins in the
shade. This method results in a firm ripe pear and the best dried
product.

Prunes normally drop to the ground when mature but in some
sections they may remain on the tree after reaching maturity. In
such cases it becomes necessary to knock the fruit to the ground for
gathering. Since prunes continue to increase considerably in sugar
content until maturity and normal dropping it is advisable to delay
knocking as long as possible in order to secure the maximum yield of
dark skinned, fine flavored fruit.

The yield and quality of raisins bear a direct relation to the Balling
degree (sugar content) of the grape juice. To obtain raisins of first
quality, Muscat grapes should not be picked below 25° Balling, or
Sultanina grapes below 23° Balling. The higher the Balling degree
of the grapes at picking, the less will be the shrinkage during drying,
the greater will be the acre yield of raisins and the higher will be the
percentage of the larger sizes, as illustrated by observations on Muscat
raisins at the Kearney Vineyard, given in Table 5.

In any case raisin grapes should not be picked for drying until
such time as they have attained the highest possible sugar content
consistent with safety in completing drying in favorable weather.
While the flavor and color of grapes indicate their condition fairly
well, the most reliable index of maturity is the sugar percentage of
the juice. This is easily and quickly measured by the use of a Balling
hydrometer which floats in a sample of the grape juice at a level
indicating the percentage of sugar. While a Balling degree of 25°
is most desirable, it is often necessary in certain sections or in certain
years to pick the grapes at 22° to 24° Balling.

TABLE 5

Eelation of Sugar Content of Grapes to the Drying Ratio, Yield and

Grades of Muscat Eaisins*

Balling

Drying
ratio

Pounds
per acre

Percentage of grades

degree of
juice

4 Crown

3 Crown

2 Crown

Seedless

Waste

18.6

4.6

2950

7.5

66.0

23.3

1.6

2.1

20.2

4.3

3050

7.5

.68.8

21.5

1.1

1.0

21.8

3.9

3032

8.3

70.2

19.0

1.5

1.0

23.6

3.6

3191

12.8

68.7

15.4

2.4

0.8

24.0

3.5

3414

20.3

64.8

13.0

1.4

0.6

26.5

3.3

4363

30.4

56.6

12.3

0.7

0.2

Reported by Professor F. T. Bioletti.

12 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

With the exception of prunes and figs, which generally fall
naturally to the ground when mature, fruits should be picked from
the tree and not knocked to the ground for gathering. When fruit is
knocked or shaken from the tree a certain amount of green fruit is
inevitably brought down with the ripe and the fruit becomes more or
less bruised and dirty in striking the branches or ground in its fall.
When a few very hot days cause the rapid ripening of an entire
orchard of apricots, or peaches, hand picking may become too slow,
especially if labor is inadequate. Under such conditions it becomes
necessary to gather the fruit more rapidly by first knocking it to the
ground. Striking the branches with poles may injure the fruit spurs.
It is safer to shake each branch by the use of a long pole provided with
an iron hook. Small trees can often be sufficiently shaken directly by
hand. Experienced pickers can obtain all the ripe fruit by this method
without bringing down much green fruit. Where the soil is soft
and loose in texture and has been well smoothed before picking, injury
to the fruit is minimized. In some sections a large canvas is spread
under the tree which not only prevents the fruit from coming into
contact with the soil but greatly facilitates transferring the fruit to
lug boxes. In general, however, the most successful growers have
found that the slightly greater cost of hand picking which makes it
possible to exclude immature fruit is overbalanced by the better quality
and greater yield of the dried product.

Wind-falls should be picked up frequently, preferably every morn-
ing, as the bruised fruit deteriorates very rapidly when lying on the
ground in the sun.

PREPARATIONS FOR DRYING

Cutting. — Pears, apricots and peaches are cut in half and the last
two pitted. Halved fruits have become the trade standard because of
their superior appearance and the greater readiness with which they
may be prepared for the table. Furthermore, halved fruits absorb
sulfur fumes and dry much more rapidly than whole fruits. Internal
defects caused by split pits, worms, etc., are revealed and such fruits
trimmed or discarded.

Cutting is invariably done by hand and should result in two equal
halves with cleanly cut, smooth edges. Various types of special cutting
and pitting knives have been introduced but possess no advantages
over an ordinary sharp knife in the hands of experienced cutters.
Cutting machines have been introduced but have not so far been
adopted in dry yards. For satisfactory results the fruit must be fed
into the machines by hand, after which as in hand cutting the halved
fruit must be spread on trays, cut surface up.

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

13

FRUIT DRYING
ORDER OF OPERATIONS

TEARS

PRUNES

PEACHES ,

CRAPES

HHniuiuti) OH

<JR

APRICOTS

FIGS

STORING

Fig. 2. — Fruit drying, order of operations.

14 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

Apricots can be dried whole after lye dipping and sulfuring but
despite their excellent flavor and lower cost of preparation are so far
in little demand and bring a comparatively low price. The pits of
apricots may be forced out by pressure between the thumb and fore-
finger after the fruit has been softened by thorough sulfuring but the
product is unattractive and of little commercial importance.

Most fruits are not peeled before drying. The fuzzy skin of peaches
is preferably removed after drying by a patented process. Peaches
may be lye-peeled as for canning or the skins may be slipped off after
sulfuring but such peeling reduces the yield and increases the cost of
the product.

The pits should be collected and sun-dried. Apricot pits are a
valuable source of by-products. An edible fixed oil, the volatile oil of
bitter almonds and macaroon paste are being manufactured from the
kernels. For this purpose the dry pits have been bringing about $40
a ton. Peach pits contain a much smaller percentage of kernels and
are not now in demand for by-products but make an excellent fuel
which may bring as high as five to ten dollars a ton.

Dipping. — Prunes and some grapes are immersed in a hot dilute
alkaline solution for a few seconds before drying. Dipping cleanses
the fruit and removes the waxy bloom. This results in a clean, glossy
product. The hot alkaline solution produces minute cracks or checks
in the skin which greatly facilitate the evaporation of moisture during
drying. Ordinarily, grape dipping is largely confined to the Sultana
and Sultanina (Thompson Seedless) varieties grown in the Sacra-
mento Valley where it aids in securing rapid and complete drying.
If dipping is followed by sulfuring, the sulfur fumes penetrate the
fruit more rapidly and completely. Dipping should be followed by
rinsing in fresh water to free the fruit from adhering lye solution
which is invariably more or less dirty.

White figs are frequently dipped in a cold solution containing salt
and sometimes lime. The function of this process is to cleanse the
figs and make them moist for more efficient sulfuring.

Sulfuring. — Apricots, peaches, pears, Silver prunes and some
grapes are exposed to the fumes of burning sulfur after cutting or
dipping and before drying. When sulfur burns it combines with the
oxygen of the air to form a gas, sulfur dioxide. This gas has the
property of dissolving in water to form a mild acid known as sulfurous
acid. This action may be represented graphically as follows.

S + 02 = S02 + H20 ~ H2S03
Sulfur + Oxygen = Sulfur Dioxide + Water = Sulfurous Acid.

Bull. 388] PRINCIPLES OF SUN-DRYING FRUIT 15

Without the presence of adequate moisture, sulfurous acid cannot be
formed in sufficient amounts to secure the desired preserving action
on the fruit. For this reason it is highly desirable to wash or sprinkle
the fruit with water before sulf uring in order that the surface may be
in a moist condition to readily absorb the sulfur dioxide gas. It has
also been observed that the higher the temperature naturally obtained
in a sulfur house, the more rapid and thorough will be the action of
the sulfur dioxide on the fruit.

Sulfurous acid in small amounts is a harmless preservative and
without its use the high commercial quality of California dried fruits
could not have been developed. Numerous substitutes for sulfur have
been tried but none have been successful. Sulfur is the standard and
practically the only preservative for dried fruits. Although con-
siderable amounts of sulfurous acid are formed in the fruit during
sulfuring the greater part of this is evaporated during drying, and
there is a further small but steady loss during storage after drying.

Part of the sulfur dioxide absorbed by the fruit combines with the
sugar and other compounds of the fruit in such a way that it cannot
be separated from the fruit without destroying the merchantability of
the product.

However, if the amount of sulfur burned much exceeds that
required to preserve a natural color, an excessive absorption and reten-
tion of sulfur dioxide gives the dried product a sulfurous taste which
is objectionable to most consumers. Therefore, it behooves every
grower to restrict his use of sulfur to the minimum amount found
necessary to properly preserve the color of the fruit in order to
maintain the good reputation of California dried fruits.

The principal effects of sulfuring are briefly described as follows :
It ' ' fixes " or " sets ' ' the natural colors of fruits and prevents darken-
ing by oxidation during drying (see fig. 1). This action is sometimes
termed bleaching. This is incorrect, although dark spots on light
colored fruits are sometimes temporarily bleached. Sulfuring kills
insects and the sulfurous acid prevents fermentation and molding dur-
ing drying and storage. The absorption of sulfurous acid ruptures the
cells of the fruit more or less and draws moisture into the pit cavity.
This results in a more rapid evaporation of moisture during drying.

PRESERVATION BY DRYING

Sun-drying, or the evaporation of moisture by the action of solar
heat and natural air currents, is the oldest form of food preservation.
Since the beginning of history, fruits, vegetables, cereals, meats and
fish have been preserved in the dried form. If properly understood,

16 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

sun-drying is at once the simplest and most economical method of food
preservation. By this means vast quantities of fresh fruits ripening
during a period of a few weeks are rapidly reduced to a durable con-
centrated form for subsequent transportation throughout the year to
all markets of the world.

A certain amount of moisture is essential to the development of the
microorganisms such as yeasts, molds and bacteria which are the cause
of spoiling and decay. Fresh fruits contain from 60 to 95 per cent of
water and spoil rapidly, but if their moisture content be reduced by
evaporation to between 20 and 25 per cent, such spoiling can not occur.
In practice, however, growers must dry fruits to a moisture content
of 16 to 20 per cent in order that the fruit will be sufficiently dry to
permit of the absorption of 5 to 10 per cent moisture- during the neces-
sary processing in the packing house, without increasing the moisture
content to an amount which permits spoiling. It is not necessary to
evaporate all the water in the fruit, because when sufficient water
has evaporated that which remains forms with the sugar in the fruit,
what may be considered a concentrated syrup. The' concentration of
sugar becomes so high that it acts as a natural preservative in which
microorganisms are unable to develop. If the fruit has been sulfured
it may be packed at a higher moisture content because of the added
preservative action of the sulfurous acid.

As a result of sun-drying, fruits undergo material changes in color,
flavor and texture to which the consumer has become accustomed and
which have therefore become the trade standards. No loss of food
value results from proper drying.

Evaporation means the change of water from the liquid to the
vapor form. The heat required for this change may be obtained by
direct radiation from the sun or indirectly from air currents heated
by the sun's rays. Without the absorption of a certain definite amount
of heat for each pound of water evaporated, drying can not take place.
The water vapor driven off by this heat is absorbed by the surrounding
air but a given volume of air at a given temperature can only absorb
a certain amount of water vapor. This emphasizes the importance of
air circulation in removing the partially moisture laden air from
immediate contact with the product being dried and in replacing it
with drier air so that the air may not become saturated and prevent
further evaporation. Summarizing the factors governing sun-drying,
it may be said that the rate of drying will be the greater :

1. The higher the temperature of the air,

2. The lower the relative humidity of the air,

3. The more rapid the circulation of the air.

Bull. 388] PRINCIPLES of sun-drying fruit 17

While in artificial drying these factors can be satisfactorily controlled,
little control in sun-drying is possible except that in very hot weather
the product may be dried by air currents in the shade, thereby avoid-
ing the more intense heat of the direct sunshine. In sun-drying most
of the evaporation takes place during the day since at night the tem-
perature of the air is lower, the relative humidity higher and the
amount of air movement generally less.

After preparation, the trays of fruit are nearly always spread on
the ground in the direct sunshine for one or more days according to
the temperature and the particular practice followed. The first
direct exposure warms up the fruit and quickly dries the surface. In
addition, the sunlight causes what has been termed an "after-
ripening" of the color of fruits. This means that a uniform deep
rich color is acquired by all the pieces of fruit. Fruit dried exclusively
in the shade retains more nearly the original uneven colors of the
fruit. Immediately after this first part of the drying, which results
in the evaporation of from one to three-fourths of the moisture, the
trays are stacked so that the remainder of the drying may proceed
more slowly in the shade. This method, known as stack drying, has
several advantages. The fruit will often be freer from wind blown
dust. Protection from the direct sunshine results in a softer skin
and prevents excessive darkening and loss of flavor. Since the final
evaporation proceeds more slowly, the dryness of the pieces of various
sizes more nearly approaches equality and over-drying, with conse-
quent loss in weight, is avoided.

Drying Ratio. — The term drying ratio is commonly used to desig-
nate the relation between the weight of the fresh fruit and the weight
of the dried fruit obtained from it. It is expressed as a ratio of the
number of pounds of fresh fruit required to produce one pound of
dried fruit, as for example, a 5 :1 drying ratio for apricots. This
ratio includes all losses in weight, chief among which are evaporation
of water during drying and losses in preparation such as pitting, trim-
ming, coring, etc. It also includes incidental losses which can be
largely eliminated by careful practice. Among these should be men-
tioned loss of material during preparation ; spilling of juice from the
cups of sulfured fruits ; loss in weight by evaporation of carbon dioxide
and alcohol formed by the partial fermentation of sugar during drying
of unsulfured fruits. This loss in weight because of fermentation has
been found to be considerable in prune drying and is greatly increased
by unfavorable drying weather.

18 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

STORAGE AFTER DRYING
Determining Proper Degree of Dryness.

The characteristics of fruit when properly dried cannot be
explained adequately here and are to be learned by experience rather
than from printed directions. In general, however, it may be said
that fruit is sufficiently dry when it is no longer soft, puffy or juicy in
the center and yet is not so dry and hard as to rattle when the tray
is shaken. It should not be possible to separate the skin by hand
rubbing. It must be firm and yet uniformly soft and pliable like
chamois skin. When a handful of the fruit is squeezed together
tightly and then released the individual pieces should drop apart
readily. Although it is a fundamental fact that the lower the moisture
content the better will be the keeping quality of the dried fruit,
excessive drying merely results in a loss of weight and therefore of
profit. Since most processing methods necessarily add a little water
to the fruit before packing it is obvious that the fruit must be suffi-
ciently dry to absorb this added moisture without exceeding the limits
for spoilage.

Equalization of Moisture During Storage.

It is impossible to have all the pieces of fruit on a tray dried to the
same degree at the same time because of the lack of uniformity in the
size, composition and preparation of individual fruits. Therefore,
when most of the fruit is considered sufficiently dry for storage it is
emptied into large boxes or bins to undergo an equalization of moisture,
commonly referred to as ' ' sweating. ' ' During this process the moisture
contents of over-dried and under-dried pieces of fruit are equalized
either by direct absorption through contact or by translocation of the
moisture by evaporation and absorption. This equalization, which
also blends and standardizes the quality of the product, must precede
the final processing and packing.

The storage place should be clean, dry, dark, well ventilated and
protected from rodents and insects so that the fruit will suffer little
or no deterioration during storage. As soon as the necessary equaliza-
tion has been accomplished, which will usually be within two or
three weeks, it is generally advisable to deliver the product at the first
opportunity to the packing house for grading and storage.

The processing and packing of dried fruits is ordinarily not con-
ducted by the grower, but is a distinct and separate operation con-
ducted in large centrally located packing houses by persons experienced
in the methods. This phase of the industry is not described in this
publication.

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

19

Fig. 3. — Typical dry yard scenes.

20 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

EQUIPMENT FOR SUN-DRYING FRUITS
DEY YAEDS

With the exception of undipped grapes which are dried between
the rows in the vineyard and some figs which are cured in the orchard,
all fruits are brought to an open dry -yard for preparation and drying.
The concentration of all operations at one place set aside for the
purpose is economical of time and labor.

The dry-yard should be conveniently located with respect to the
orchard or vineyard and away from all dusty roads and barn yards.
Roads required for hauling fruit to and from the dry-yard should be
so located that the prevailing winds will blow the dust away from and
not over the drying fruit. The dry -yard should have a sunny exposure
free from shading trees, and preferably a slight slope toward the
south. Larger yards where cars and tracks are needed should be
sufficiently level to permit their use. The area of dry-yard required
will vary from one-third to one acre for each ten acres of orchard or
vineyard ; according to the orchard yield and the speed of drying. In
general, 1 to 20 is a safe average ratio.

The surface of the ground should be handled in such a way as to
prevent dust blowing on the fruit during drying. Some excellent dry-
yards, as illustrated in fig. 3, are never cultivated but the ground is
allowed to become solidly packed and free from loose dust or vegeta-
tion. A more common practice is to grow grain or hay and spread
the trays on the closely cut, well raked stubble after harvesting. This
usually necessitates the relaying of portable tracks each year, but
realizes a return from the crop harvested. The stubble should never
be burned before the drying season as this causes the fruit to become
unsightly because of wind blown bits of charred straw. A closely cut
and not recently irrigated alfalfa field is very satisfactory for peaches
and apricots but for the slower drying prunes or grapes in cooler
sections may unduly increase the drying time. The contamination of
dry -yards and drying fruit by animals or poultry must be carefully
guarded against by adequate fencing.

Foreign matter which lodges on the surface of cut fruits during
drying can not be satisfactorily removed in the packing house and,
therefore, seriously lowers the quality of the product. Consequently
the dry-yard should be so prepared and managed as to minimize
contamination of the fruit during drying.

Bull. 3S8]

PRINCIPLES OF SUN-DRYING FRUIT

21

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3 fi

O- o

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22 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

All but the smallest yards should be provided with a system of
tracks and cars for moving the trays of fruit between the various steps
in preparation as well as to and from the spreading ground. Hand
carrying or the use of a horse and wagon are generally less eco-
nomical and sanitary. Miniature steel railroad tracks with either
steel or wooden ties are the most substantial and permanent, although
wooden rails, if faced with strap iron or angle iron, are satisfactory.
Such tracks may be either permanently installed or portable but in
either case should be smoothly laid so that the juice in the cups of
freshly sulfured peaches and apricots is not spilled during transporta-
tion. The arrangement of tracks with respect to the dipping or cut-
ting shed, sulfur houses, dry-yard and dried fruit storage space should
be such that the fruit moves forward steadily through the various
operations with the minimum retracing of routes. Empty trays and
cars should be returned to the reloading point without coming in con-
tact with loaded cars. The amount of trackage must be determined
by the quantity of fruit handled daily and the area and shape of the
dry yard.

Fig. 5. — Turntable for changing direction of tray cars.
(Cut furnished by Anderson Barngrover Co.)

The usual type of tray car, as illustrated in fig. 4, consists of a
low wooden frame about 3' x 6', supported by four cast-iron wheels
on steel axles. Such cars will carry from 20 to 25 3' x 8' trays holding
from 1000 pounds of apricots to 2000 pounds of prunes. In order to
provide the necessary flexibility in the transportation system as in
moving cars in and out of sulfur houses and to various parts of the
dry yard, use is made of steel or wooden transfer cars or of turn
tables sunk below the standard track level so that the tray cars can
be run on them for movement at right angles to their previous direction
(see figs, 4 and 5).

Figure 6 shows a suitable arrangement for a 2% acre dry-yard
equipped to handle cut and sulfured as well as dipped fruits. It is not
expected that this plan will fit all conditions but should serve as a
guide in planning a well arranged dry -yard.

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

23

Space for dry ma pi

<h- s-ogu<je Ttach ?

C uttino Shed and Tab/es

E^kCZI CZI EU CD CD

Dr y yard Sp<

STm

CD CD CD CD CD CD

y yard Spac

Ground plan of a
\ Dry yard- Approx.2%A

This yard will accomodate
Qpprox. So acres, of orchard
ot 5 areen Tons per- A

Fresh FruiT
Spac.

Prune dippt
and qrader

Fig. 6. — Ground plan of a dry-yard.

w

Cgj)

©

CUTTING SHEDS

While small quantities of fruit are frequently cut and trayed
under the shade of trees adjacent to the dry-yards, the use of an
inexpensive shed is generally desirable, not only to protect the cutters
and the fruit during preparation but to serve as a convenient storage
place for trays, boxes and other equipment during the winter. For
most orchards an open shed, with a tight roof, sufficiently large to
accommodate the number of cutters employed, is adequate. It should
be so located that prevailing winds will not blow fumes from the sulfur
houses toward it and may be walled on one or more sides to give pro-
tection from wind-blown dust or sulfur fumes. Ample light and
ventilation are necessary for efficient work by the cutters.

The fruit is unloaded at one end or side of the shed and carried
to the cutting tables as required. An inexpensive and convenient cut-
ting table, designed to hold one 3' x 8' tray or several smaller trays
and provided with brackets on both sides to hold boxes of fruit for

24

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

cutting, is shown in fig. 7. The track for loading cars should be
adjacent to the rows of tables so that each tray as it is filled may be
placed on a car and replaced by an empty tray. The floor of large

-7-

VI an for C aft i no Table

TopVi

ew

/

h-6-^

Side V/ew

8

->~«^-h

"kw1 W.M IWA1^

It

■Alh

h
u

End l//ew

Fig. 7. — Plan for fruit cutting table.

sheds where much trucking is necessary should be of wood or concrete
but in small sheds the natural ground may be used if sprinkled daily
to prevent dust rising. The comfort afforded cutters by stools results

Bull. 3S8]

PRINCIPLES OF SUN-DRYING FRUIT

25

in greater efficiency. Sharp knives and small pans or boxes for the
collection of pits and spoiled fruit are necessary to secure cleanly cut
fruit. Water, soap and paper towels should be provided so that the
cutters may frequently wash their hands and knives. Sanitary toilets
and drinking fountains are sanitary requirements. A small supply
of iodine, bandages and adhesive tape is necessary "first-aid" equip-
ment for cuts or scratches. Cards on which are marked or punched

H±z

Fig. 8. — Dump basket, prune or grape dipper, with lye tank and furnace.
(Cut furnished by Anderson Barngrover Co.)

the number of boxes of fruit cut by each person daily furnish a simple
and invaluable record of the payment due to cutters and of the amount
of fruit handled. In fairness to the cutters and as a record of the
amount of fruit picked and cut each box should be made up to the
same net weight before cutting.

DIPPEES

Basket dippers are used for both grapes and prunes. The simplest
type illustrated in fig. 8, consists of an oblong basket with a rounded
bottom of perforated sheet metal or wire screen. This basket is hinged

26 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

to one edge of the lye tank so that after immersion the basket may be
raised by a lever, the fruit drained and emptied directly on to the tray
or into a small bin or a shaker which in turn discharges on to the
trays. Another type, known in Sutter County as the "Merry-go-
round," and used especially for Sultanina (Thompson Seedless) types,
suspends the basket from an over-head counterbalanced beam which is
fastened to a pivoted upright. The fruit is emptied into the basket at
one point, the basket swung over the lye tank and submerged, removed
from the lye tank and swung to the other side for discharging the
grapes on to the trays. If two opposite baskets are used, loading and
unloading may proceed simultaneously, the baskets describing a com-
plete circle for each load. Continuous automatic dippers consisting
either of an endless draper or a series of baskets supported by two
endless chains, are used in a few of the larger grape dry-yards.

Rotary Dippers are used only for prunes and consist of a rotating
perforated metal cylinder the lower third of which is submerged in
the lye solution. The prunes are emptied in at one side and, by means
of vanes set at the proper angle on the inner walls of the drum, are
carried down through the lye solution and discharged at the opposite
side. These dippers, illustrated in fig. 9, are automatic and continuous
and have the greatest capacity. They are operated by a gas engine
or electric motor and the speed of rotation can be varied to regulate
the time of immersion. Rotary dippers can be provided with a vibrat-
ing screen on which the prunes are emptied for separation of dirt and
leaves, before entering the dipper. This results in cleaner fruit and
prevents the lye solution becoming dirty so rapidly.

Lye tanks have a capacity of from 100 to 200 gallons and are
mounted in a rectangular brick furnace. Wood is used by some as a
source of fuel but the majority use some of the forms of oil burner
because they can be made to maintain a constant temperature with very
little attention. The less expensive natural draft burners require a
refined oil such as kerosene while forced draft burners utilize the less
expensive stove oil or even crude oil. In a few places the lye tank is
heated by steam coils but this system is not recommended unless a
steam boiler is required for other purposes.

LYE

The lye used in dipping is sodium hydroxide or "caustic soda."
The commercial product, granulated or in flakes, contains 95 per cent
or more of sodium hydroxide, the active ingredient. It should be kept
in tight metal containers to prevent absorption of moisture from the
air. Some brands of "lye" consist partly of sodium carbonate or

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

27

28

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

"sal soda," a compound which is not so strongly alkaline as sodium
hydroxide but gives equally satisfactory results if used in sufficient
strength. The stronger sodium hydroxide is preferred for prunes,
while the milder sodium carbonate either alone or in combination with
sodium hydroxide is largely used on the more easily affected Sultanina
(Thompson Seedless) grapes. Sodium bicarbonate or "baking soda"
is another and much weaker alkaline salt which is used in the dipping
of "oil bleached" raisins.

Fig. 10. — Hand-operated basket prune dipper, with lye tank and furnace,
connected to power-driven grader. Tray supports in foreground. (Cut furnished
by Anderson Barngrover Co.)

GRADERS

Graders are used in conjunction with most of the larger prune
dippers. The dipped prunes are separated into two or three sizes by
passing over vibrating screens which can be changed to suit the sizes
desired. This so-called "green grading" is valuable in securing more
even drying by placing the small and large prunes on separate trays.
If grading is not done, the small prunes may be over dried when the
large ones on the same tray are still too moist. This necessitates extra
trays and sorting. A small grader is illustrated in fig. 10.

BULL. 388] PRINCIPLES OF SUN-DRYING FRUIT 29

Needle hoards are often incorporated with graders. They consist of
a flat vibrating board or sometimes a rotating cylinder, each studded
with short sharp needles, and are frequently used to supplement the
dipping of prunes. When prunes of varying degrees of maturity are
dipped together, the skins of those which are not checked by the lye
solution are at least punctured by the needles, providing apertures for
the rapid and even evaporation of moisture.

TEAYS

The most common sizes of trays used are the 2' x 3', 3' x 6' and
3' x 8', illustrated in fig. 11. Other sizes have no special advantages
and are seldom used. The 2' x 3' tray is referred to as the raisin tray
because it is universally used in the natural drying of raisins in the
vineyard. In the raisin sections it is also used for peaches, apricots
and figs. The 3' x 6' tray is used for peaches, apricots, figs and dipped
grapes, especially seedless. It is also used for prunes and pears
although in Lake County a special tray, 2%' x 7' is preferred for
pears. The 3' x 8' tray is preeminently the prune tray but is also used
for peaches, pears and apricots. Table 6 gives the usual specifications,
capacities and costs of the standard trays. It must be borne in mind
that the weight of fruit which can be spread in a single layer on one
square foot of tray surface varies considerably with the size of the
individual pieces of fruit. Unless below average size, apricots can be
spread at the rate of two pounds and peaches three pounds per square
foot. Pears and prunes vary from three to four pounds per square
foot but not usually less than three and one-half pounds. Muscat
grapes do not fall below three and one-half pounds per square foot
but seedless grapes are usually spread about three pounds per square
foot.

The number of trays required to sun-dry a given tonnage of fruit
during the season varies greatly with the rapidity with which the fruit
ripens and drys. Prune and raisin trays are generally used but once
each season and it is therefore necessary to have sufficient trays to
spread the entire crop. Trays for peaches and apricots are generally
used two or three times during the season and the number required
is proportionately less. In estimating the number of trays required to
dry the fruit from a given acreage, the tonnage of fruit per acre
becomes another factor of variation. Table 7 gives the approximate
number of standard trays required to dry various fruits. Such figures
are subject to great variation but the limits stated in Table 7, cover
most cases.

30

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

SUWAQD tyPLS
OF tWlC OJAYS

Scale :- *m.= 1ft.

1

' '

1 1

1

1

!

I

i .r- -i

J

MATERIAL FOR 3'* 6' TRAY

2. Pieces
2. •'
3 -
16 "

1i"» 12"-3iir

r- i8r"« 8'

xr= 1 1 i=

i — """ — | I i =

-u 1 1 i,

=i j — i-

MATLR1AL FOR 5*6' TRAY
% P.eces S"*lf*6'

MATERIAL FOR £» 3' TRAY

2 Pieces -
X " -
5 » -
1 » -

l"'iV'o'

8' 6*0
/6 " 11 " Z

Fig. 11. — Standard types of fruit trays.

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

31

TABLE 6
Specifications, Capacities and Costs of Standard Field Trays

Standard specifications

T x 3' Trays

3' x 6' Trays

3' x 8' Trays

End cleats

2-^"xlM"x3'
2-^"x y8"x3'

2- %"xi%'xe'

3- ^"xlM'W
12- i4"x5M"x3'

18'

30-36
40-50
54-66
45-60
54-72
54-72

$.73
$.78

2-WxWx34M"
2- K"xlK"x8'

Side cleats

Clinch cleats

3- ^"xlM"x8'

Bottom boards

5-^"x5M"x2'

1-^"x7K"x2'

6'

10-12
13-17
18-22
15-20
18-24
18-24

$.17
$.20

16- %"x5%"x3'
24'

Gross area in sq. ft

Average capacity in lbs.:

Apricots

Figs

40-48
53-67

Grapes

72-88

Peaches

Pears

60-80
72-96

Prunes

72-96

Approximate cost:

[j| In shook

Made up

$.90
$1.00

TABLE 7
Number of Trays Kequired for Sun-Drying*

Apricots

Figs

Grapes:

Muscat....

Sultanina

Peaches

Pears

Prunes

2' x 3' Trays

Per ton Per acre

30-45
15-20

90-100
110-120
35-45
40-80
44-60

150-500
30-40

315-350
520-570
260-340
200-400
220-760

3' x 6' Trays

Per ton Per acre

10-15

5-7

30-33
37-40
12-15
13-27
15-20

50-166
10-13

105-117

173-190

87-113

65-130

73-253

3' x 8' Trays

Per ton Per acre

8-11
4-5

23-25
28-30
9-11
10-20
11-15

38-125
8-10

80-88
130-143
65-85
50-100
55-190

* Calculated from observations on seasonal tray requirements for given tonnages and acreages of fruit .

Pine is the most common kind of wood used for trays. Trays with
spruce frames and pine bottoms are considered by some to be more
sturdy and longer lived. Redwood is used in some sections because
of its lower cost. Redwood trays, especially when new, have been
known to stain moist light colored fruits such as peaches, pears and
apricots but are satisfactory for prunes. In constructing trays the
rougher side of the bottom boards should be up because dried fruit

32 • UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

sticks less and is more easily removed from rough than smooth sur-
faces. Heavy wrapping paper obtainable in bundles of 2 reams or 960
sheets is used for drying raisins in the vineyard when wooden trays
are unavailable. Paper trays are less suitable because raisins can not
be properly turned or stacked on such trays and in case of rain may
result in the loss of raisins because the wet paper can not be handled.
Furthermore, paper trays hold less grapes, more are spilled on the
ground and more dirt incorporated with the raisins. Although lower
in first cost (about 1 cent each), paper trays must be replaced yearly
and are, therefore, if we consider decrease of quality and losses from
rain damage, more expensive in the long run than permanent wooden
trays.

Clean trays are necessary for the production of clean dried fruit.
If trays become dusty, sticky or moldy they should not be used until
they have been washed and dried. If properly handled such washing is
generally necessary only at the close of each season. The use of a stiff
bristle or wire brush will remove all dirt after it has been softened by
immersing the tray in a hot solution containing sal soda, After
rinsing, the trays should be sulfured and thoroughly dried to prevent
molding during storage. It is preferable to store trays in some sort
of building or shelter which keeps the trays clean and dry and by
protecting them from the weather lengthens their useful life.

SULFUR HOUSES

Many types and sizes of sulfur houses, varying in their cost and
efficiency, are in use. The simplest and cheapest type is known as the
sulfuring "hood" and consists of a light wooden framework covered
with building or roofing paper (see fig. 12). It is open at the bottom
and of such a size that two men can lift it up by the handles and place
it over a stack of trays on the ground. The sulfur is burned in a hole
in the ground or preferably in a pan or bucket set on the ground inside
one end of the hood which should be made at least a foot longer than
the stack of trays. Earth is shoveled against the bottom of the hood
to prevent escape of sulfur fumes. Such hoods are highly inflammable,
not very tight, and their useful life is limited to a few seasons. Their
use is not recommended except in emergencies or for very small scale
operations.

The most common sulfur house is built of wood made as tight as
possible either by the use of tongue and groove lumber or by common
boards lined with building or roofing paper. A tight fitting door at

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

33

one end permits the entrance of a truck of trays which is rolled into
the house on tracks. Houses of concrete, brick or hollow tile are
always tight and fire-proof (see fig. 13) but are not recommended for
the efficient sulfuring of fruit with the minimum amount of sulfur
because of the retarding influence of the cold air resulting from the
resistance of these materials to heat penetration. Heavy beveled doors
with locks of refrigerator type are the best.

Top V/eur

Src/e V/eW

Q a /loon Hood

/"x<?" Wooden Frame Covered
Wrffl 3 P/y Budd,„a PaPer.

fnd Viet*

< — >B"-i

L_^__^

1 v«l

i

1 J.

\ — -i-l -!

.1

SO

1

Fig. 12. — Balloon hood sulfur box.

For efficiency and economy in sulfuring, the main essentials of
sulfur house construction are :

1. Tight construction to prevent leakage of sulfur fumes.

2. Materials of construction which permit warming the interior by
penetration of solar heat.

3. Adequate space and protection for the sulfur burning equipment
to minimize fire hazard.

Recent investigations by R. S. Hiltner, Technologist of the Dried
Fruit Association of California indicate that a sulfur house built of
flat sheet iron painted outside and inside with black asphalt paint to
resist rust and corrosion fulfills the above requirements.

34

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

35

Common sulfur houses as illustrated in figs. 14 and 15, are usually
a little over 3 feet wide and 6 to 7 feet high inside. The length should
be about 2 feet more than that of the car of trays, to provide space
for burning sulfur. A number of houses sufficient to accommodate the

l*£n£ai

■-L-.'iiV

JV-

Fig. 14. — Typical sulfur houses with counterpoised door hinged at top.
Note transfer and tray cars.

Fig. 15. — Typical battery of wooden sulfur houses, each with capacity of
two cars. Note sliding doors and counterweights.

daily output of the cutting shed are arranged in a row with a track
and transfer car along the front to facilitate entrance of tray cars into
each house. In large dry yards the houses are often built long enough
or wide enough to hold two cars.

36

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

H h--t— 4-

Certter

hr?e

of hoys

V

TOP VIEW

Root

k//fur dioxide e$cap//?Q.

ype car? be easily
iaker? apart at
f/p/b Jo/r?f.

Fig. 16. — Metal sulfur-burning stove and distributing flue inside a tight
sulfur house. (Courtesy of Dried Fruit Association of California.)

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

37

Rear Yval/

Grour?c/ line—^
Pi pi

Fig. 16A — Concrete sulfur-burning stove and distributing flue outside a tight
sulfur house. (Courtesy of Dried Fruit Association of California.)

38 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

While the sulfur can be burned in a small pit in the ground, a
better practice is to use a clean pan or bucket placed either on the floor
inside the door or by means of a small opening for this purpose in the
rear of the house. Such containers afford easy measurement of the
sulfur and insure complete combustion without waste. Where the
minimum necessary quantity of sulfur is used, it is essential that com-
plete combustion of the sulfur and uniform distribution of the result-
ing gas throughout the house be secured. A sulfur stove, preferably of
brick or concrete, with a distributing flue as illustrated in fig. 16, has
been found to cause complete combustion and distribution of the
sulfur fumes.

If such stoves are used, it is unnecessary to provide openings in the
house for admission of additional air because, even if the sulfur house
be hermetically sealed, it contains sufficient oxygen to burn at least
two pounds of sulfur per ton of green fruit.

The number of sulfur houses required is dependent on the acre-
yield and the rate at which the fruit is picked and cut. With peaches
and apricots, each sulfur house will care for from four to ten acres
of orchard during the season, an average being one house to six acres.
Each house can rarely be used for more than two trucks or from one
to two tons of fruit daily. Since pears are normally sulfured 24 hours
or longer, the number of sulfur houses required will be 2 or 3 times
that required for peaches or apricots.

SULFUR

Any kind or brand of sulfur which is free from arsenic and will
burn readily can be used in fruit drying. The kind most commonly
used is known as sublimed flowers of sulfur. The light fluffy texture
of this refined sulfur is such that it is readily ignited by a match or a
bit of burning paper and burns steadily and completely without
further attention. A cheaper form of sulfur is a ground or lump
crude sulfur which is sufficiently pure for use on fruit. However,
the physical condition of this sulfur is such as to require special sulfur
burning stoves or pans to insure its combustion. These stoves or sets
of superposed pans retain enough of the heat generated by the burning
sulfur so that the sulfur burns continuously until all is consumed.
While the use of the cheaper crude sulfur should result in a slight
saving, most growers prefer the flowers of sulfur because it obviates
the necessity of special stoves or pans and of frequent attention to the
sulfur fires. All sulfur should be kept in a dry place to prevent

Bull. 388] PRINCIPLES OF SUN-DRYING FRUIT 39

absorption of moisture which would interfere with combustion. The
admixture of not over 5 per cent of powdered sodium or potassium
nitrate (saltpeter) (one pound to 20 pounds of sulfur) insures com-
plete combustion even under adverse conditions.

SWEAT BOXES AND BINS

Various methods are in use for temporary storage of the dried fruit
before delivery to the packing house. Some fruits, especially prunes,
and to a considerable extent cut fruits are concentrated in large piles
on a wooden or concrete floor for storage and equalization. The dried
fruit may either be emptied into lug boxes in the dry -yard for transfer
to the storage building or the trays of dried fruit can be stacked on
cars and brought directly to the storage place for unloading. If large
tonnages must be stored on a restricted floor area it becomes necessary
to construct wooden bins, at least one wall of each being constructed of
heavy removable boards to facilitate emptying. The construction of
such bins is best learned by visiting a modern packing house. In
calculating the capacity of dried fruit bins, the factors given in Table
8 will be found helpful.

TABLE 8
Capacity Factors for Dried Fruit Bins

Average pounds
Fruit per cubic foot

Apricots 54

Figs, white 53

Figs, black 55

Peaches 49

Pears 56

Prunes 59

The common method of transferring such fruits from the growers '
bins to the packing house is in sacks, usually used grain sacks. A better
method is to use lug or sweat boxes because sacks not only require
sewing but also cause the fruit to accumulate dirt. Flat cut fruits such
as peaches and apricots become more curled up when sacked. This
results in a reduction of the percentages of the larger sizes when
graded and for this reason box delivery is preferable.

Raisins and white figs are almost invariably collected in sweat boxes
after drying in the vineyard or dry-yard. These boxes are strongly
built with ends of l1/4" and sides and bottom of %" pine, reinforced
by corner posts. They are about 38y2" x 26%" by 7%" deep and cost

40 UNIVERSITY OF CALIFORNIA— EXPERIMENT STATION

about $1.25 each. The capacity varies from 100 to 200 pounds of
dried fruit. They are used both to store and equalize the fruit after
drying as well as containers in which to deliver to the packing house.
Lug boxes are less satisfactory because of their smaller capacity but
can be used, if available in sufficient numbers, to reduce the investment
in equipment.

PRACTICES OF SUN-DRYING FRUIT
PICKING METHODS

Apricots and peaches should be picked from the tree when they have
a uniform ripe yellow color, when they have begun to soften but are
still reasonably firm and when they can be easily cut with a sharp
knife and yet retain their shape. In order to obtain only well-ripened
fruit it is necessary to pick over the orchard from two to four times
in a season. The number of pickers required per acre of orchard
averages one to four for peaches and one to two for apricots. The
average adult will pick one thousand pounds of apricots or two
thousand pounds of peaches a day. If knocked to the ground for
gathering, these figures will be considerably increased but the fruit
will be bruised and uneven in ripeness. The average cost of hand
picking is three dollars and fifty cents per ton of peaches and seven
dollars per ton of apricots.

Figs drop naturally to the ground when mature. The ground
should be smoothed, to keep the figs cleaner and easier to gather. The
trees may be lightly shaken but the fruit should never be knocked off
with poles. The fallen figs should be gathered frequently as exposure
causes them to become sunburned, dirty and infested with insects.
In practice, however, it is rarely possible to cover the orchard more
than once or twice a week.

A simple and economical method is used with Mission figs in the
Winters district. The fallen figs are picked directly into sacks, which,
when one-third to one-half full, are tied and flattened out on the
ground under the tree half way out from the trunk. The sacks are
turned every two or three days until the figs are uniformly dried when
several sacks are condensed for hauling to storage bins. Very uniform
drying results in dry weather but the figs are apt to become excessively
dirty and accumulate lint from the sack.

The entire cost of picking and drying by this method is about $17
per dry ton and requires one picker to each two acres.

BULL. 388] PRINCIPLES OF SUN-DRYING FRUIT 41

White figs picked into boxes require about one picker to each eight
acres, at the rate of one thousand pounds per picker daily. The cost
of picking averages ten dollars per dry ton.

Pears are picked from the tree when hard ripe and still green in
color and when the stem separates readily from the spur. It is neces-
sary to pick over the orchard two or three times in order to secure
pears of even maturity. Windfalls should be gathered frequently,
preferably daily. In some orchards a layer of straw is spread under
each tree to minimize bruising and keep the pears clean.

Grading and Ripening Pears. — When received at the preparation
shed, pears should be graded before ripening in order to obtain even-
ness in both ripening and drying. Grading may be accomplished by
hand or by special pear grading machines, the latter being more exact
and economical for large plants. Wormy, sunburned, bruised or
blemished fruit should be separated as it not only ripens faster but
makes a second grade dried product. The sound pears are graded
into from three to five sizes, In some localities the medium sizes are
reserved for fresh shipment or canning. The various grades of each
day's picking are stacked in separate boxes for ripening, which requires
from five to ten days. During this time the pears are sorted two or
three times to remove ripened or rotten pears. In the absence of suffi-
cient boxes, pears may be ripened in shallow bins covered with a
canvas or even between thick layers of straw under the shade of a
tree or shed. Such methods, however, require more labor and result
in greater loss from rotting. Pears are ready for cutting when they
have acquired a uniform yellow color and full pear flavor, when
slightly soft to thumb pressure yet still firm and not over-ripe or
mushy.

Prunes are always picked from the ground, which should be smooth
and free from vegetation to facilitate clean and rapid harvesting. If
prunes remain on the tree after reaching maturity it becomes necessary
to shake the trees or even knock the fruit off with poles in order that
the crop may be gathered before the season becomes too late for sun-
drying.

The prune orchard is picked over on the average about four times,
at intervals of a week or more. The final picking is preceded by a
thorough shaking or knocking, in order to bring down all the remain-
ing prunes. An average crop requires one picker for each five to seven
acres. Adult pickers average nearly one ton a day, the rate of pay
varying from four dollars to six dollars a ton.

42 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

Grape pickers cut the stems with a sharp knife and spread the
bunches directly on 2' x 3' trays holding- 18 to 22 pounds each. Before
picking begins, trays are distributed between the rows and a ridge of
soil thrown up against the south side of the east and west rows. The
filled trays are placed against this ridge and are thus tilted toward the
south in order to secure the maximum effect of the sunshine. Pickers
are paid from two and one-half to five cents a tray according to the
number of trays of grapes per unit of five hundred vines, the average
being three and one-half cents a tray. This is equivalent to a cost of
three dollars to three dollars and a half per ton of grapes. Generally
the entire crop is removed at one picking.

Grapes which are dipped and sulfured before drying are picked
into boxes and hauled to a dry -yard.

Boxes of fruit should not be allowed to remain in the orchard for
more than one day after picking. They should be stacked in the
shade and delivered to the preparation shed as promptly as possible
in order that preparation and drying may begin while the fruit is in
the freshest possible condition. This is especially important with fruit
which has been bruised in falling to the ground.

WASHING

While not the general practice, washing apricots and peaches before
cutting increases the quality of the dried product and therefore the
price obtained, as has been demonstrated by comparative tests, because
the fruit is cleaned and the surface left moist for the quick and uni-
form action of sulfur fumes. This is especially true of fruit gathered
from the ground after being shaken from the tree.

The simplest method of washing consists in emptying the fruit from
the picking boxes into slat bottom lug boxes, immersing in a tank of
clean water, draining and using these boxes as service boxes to supply
fruit to the cutters.

CUTTING AND PITTING

Apricots and peaches are cut by running a sharp knife around
the line of the suture so that the knife blade returns to the point
where the cut began. The two neatly cut halves are then separated,
the pit picked out, and the two halves laid immediately on to a clean
tray with the cut surface up. The fruit should not be cut part way
around and then torn apart, as this leaves ragged unattractive edges.
The pieces are placed close together to utilize the maximum capacity
of the tray, but should not be crowded or overlapped as this causes

BULL. 388] PRINCIPLES OF SUN-DRYING FRUIT 43

the juice to spill out of the pit cavities when the trays are handled
after sulfuring, resulting in a loss of weight and sticky fruit and trays.
In order to keep the trays and fruit clean, uncut fruit should not be
emptied on to the tray but should be removed from the lug box as it
is cut and the pits thrown into a separate box or pan for collection
and drying. Overripe fruit which will make "slabs" is preferably
placed on separate trays so as to simplify culling the dried product.
Kotten fruit should not be thrown back into the lug box or with the
pits, but into a separate receptacle.

For apricots, an average of one cutter to each acre of orchard is
required. Cutters are paid from seven to twenty-five cents a box,
averaging thirteen cents, the rate being regulated to some extent by
the size of the fruit but more by the local labor supply and demand.
One person will cut from eight hundred to two thousand pounds daily,
the average being about one thousand pounds. The cost of cutting
ranges from $5 to $8, averaging $6 a ton. Cutters should be paid at
a rate per box which permits the grower to insist on proper cutting
and still enables cutters to earn fair wages. Comparative tests have
shown that improper cutting by underpaid cutters results in a greater
loss in value of the dried product than the apparent saving from
reduced cutting costs.

With peaches, one cutter for each 2 to 5 acres is required. Cutters
are paid from six to ten cents a box and average two thousand pounds
a day. The average cost of cutting peaches is $3.50 a ton.

Pears are cut through the center from calyx to stem and the stem is
pulled out. Worm holes should be trimmed out and some growers
also trim out the calyx. The core can be removed from each half by a
special steel loop pear corer. This gives the finest product but adds to
the cost of preparation and reduces the yield. Cutters are paid from
ten to twenty cents per box of 50 to 60 pounds net. The rate varies
according to the locality, the size of the pears and the amount of trim-
ming required. An experienced person can cut twenty boxes a day.
The average rate in 1922 was fifteen cents a box, equivalent to about $5
a ton.

DIPPING

Prunes should be dipped in a hot alkali solution as soon as is con-
venient after harvesting. The lye solution is made by adding 1 pound
of lye to from 15 to 30 gallons of water, usually 1 pound to 20 gallons,
which is equivalent to a concentration of 0.4 to 0.5 per cent lye. The
temperature of the dip varies, with different operators, from lukewarm
to boiling, but comparative experiments have shown the most efficient

44 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

temperature to be 200° F., which means that the dip should be main-
tained close to the boiling point. The time of immersion varies from a
few seconds to half a minute but if the temperature and lye concen-
tration are correct, from 5 to 15 seconds is ample. The strength of the
solution must be maintained by periodic additions of lye to replace that
lost mechanically and by partial neutralization of the fruit acid and at
the end of each day's dipping the lye tank should be drained and a
fresh solution made up for the next day.

Fig. 17. — Effect of proper lye dipping on the skins of prunes.

Tough skinned varieties such as the Robe de Sergeant require a
stronger solution and longer dip than more tender varieties, such as
the Imperial. Frequent examination of the dipped prunes is neces-
sary to regulate the strength of the dip and time of immersion in order
that the skins of the majority of the prunes shall develop a number of
minute cracks as shown in fig. 17. In general a short dip in a fairly
strong lye solution close to the boiling point gives better results than
a long dip in a weak or lukewarm lye. If the prunes are so tender
as to become partially peeled in dipping, it is necessary to reduce the
temperature or lye concentration or both. Some growers prefer to
dip Imperials merely in warm water to which little or no lye is added.

If the dip can not be adjusted so as to check all the prunes, the use
of a pricker board is advantageous because the skins of those prunes
not checked by the dip are at least perforated.

BULL. 388] PRINCIPLES OF SUN-DRYING FRUIT 45

Rinsing after dipping is not practiced by all growers but is
generally considered advisable. Rinsing may be done by immersing
the prunes in a second tank through which fresh water is running but
preferably by passing the prunes under water sprays.

The dipped prunes, either graded or ungraded, are discharged on to
the trays and spread close together one layer deep only. The larger
dipping outfits have a device for shaking the trays to minimize the
amount of labor required in spreading. The filled trays are then
stacked on trucks for transfer to the dry yard.

The number of men in a dipping crew varies from 3 on small hand-
power dippers to as high as 7 on the largest power dippers; averag-
ing 5. The average daily capacity for a typical dipping crew was
found to be about 7000 pounds per man. It is common practice for
the crew to dip prunes during the forenoon and to spread the trayed
prunes and do other dry-yard work in the afternoon. Recently,
mechanical tray stackers installed in some orchards have eliminated
two men from the dipping crew.

The average operating cost of dipping and spreading prunes on
trays, presented in Table 9, is based on exact measurements in over
20 dry-yards.

TABLE 9

Average Cost of Dipping and Traying Prunes

Per fresh ton

Lye, 1.3 pounds, @ 8j^c $ .11

Power, 2.5 K.W.H., @ 2c 05

Fuel oil, 2 gals., @ 8c 16

Labor, 1.95 man hours, @ 40c 78

Total SI. 10

Grapes. — Sultaninas and Sultanas are dipped before drying to
produce the three commercial grades known as : Soda Dipped, Bleached
and Oil Dipped. For the first two grades the grapes are dipped in
much the same way as that just described for prunes. If the dip
contains 1 pound of lye to every 10 to 20 gallons of water and is
nearly boiling, satisfactory dipping is obtained in five seconds or less.
Basket-type dippers must be used and the clipped grapes should be
rinsed before traying. Because of the ease with which the skins of
Sultanina grapes can be checked and of the danger of over-dipping,
most growers prefer to use weaker brands of lye containing as much
as 50 per cent sal soda.

46

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

Soda-dipped raisins are placed directly in the dry-yard while
bleached raisins are sulfured several hours after dipping and before
drying.

Oil Dipped raisins are immersed for a few seconds in a cold solution
of 30 pounds of bicarbonate of soda (baking soda) and 1 pound of
lye in 100 gallons on which a thin film of olive oil is floated. The water
may be heated to hasten the solution of soda if necessary. The soda
dissolves the waxy bloom of the grapes and causes them to dry more
rapidly. The thin film of olive oil with which the grapes become
coated gives the finished raisins a glossy lighter brown color and a
softer skin. For each green ton of grapes dipped, about 5 pounds of
sodium bicarbonate and 1 quart of olive oil are consumed.

Figs. — The Adriatic is the only variety of fig which is dipped. A
cold brine containing from 5 to 20 pounds of salt in 100 gallons of
water is the most common dip, although some growers add an amount
of lime equal to the salt. The function of this dip, which can be
applied by immersion or preferably by sprays, is to cleanse the skin
of the figs and leave them moist to facilitate the sulfuring which
follows. Comparative experiments by the writers have shown that
plain water is just as good and the expense for salt and making the
brine is unnecessary.

SULFUK1NG

Sulfuring methods vary considerably with variety of fruit, con-
struction of sulfur houses, locality, temperature, etc. The figures in
Table 10, represent what has been considered common practice.

TABLE 10
Average Amounts of Sulfur and Times for Sulfuring Fruits

Fruit

Hours exposed

Pounds sulfur
per green ton

Cost of sulfur
per green ton*

Apricots

Peaches

Pears

Grapes (Seedless).
Figs (Adriatic)

4
5
36
4
4

7
7
12
5
3

$.28
.28
.48
.20
.12

* At 4 cents per pound.

The quantities of sulfur given in Table 10 are many times the
quantity actually absorbed or required by the fruit. This is because
most sulfur houses permit a steady escape of sulfur fumes and because

Bull. 388] PRINCIPLES OF SUN-DRYING FRUIT 47

many operators cause the fruit to absorb as much sulfur as possible,
incorrectly believing that "if a drop is good, a bucketful is better."

Recent investigations by R. S. Hiltner, Technologist of the Dried
Fruit Association of California, show that two pounds of sulfur per
ton of peaches or apricots is ample to preserve the fruit provided this
sulfur is completely burned and the fumes distributed in a tight house.
For the benefit of the industry, growers should make their sulfur
houses tight and restrict the amount of sulfur burned to the minimum
required for color preservation.

In general it may be said that the best results are obtained by the
use of the minimum amount of sulfur in a tight warm sulfur house
and by allowing the fruit to remain in the house for 12 to 24 hours
after the sulfur has ceased burning.

Apricots and Peaches. — In order that the surface of cut fruits will
be moist for sulfuring, each tray of fruit should be sprinkled with
water or a weak brine (1 pound of salt to each 4 gallons of water) as
it is stacked. Salt aids in preventing the darkening of the fruit and
reduces the amount of sulfur required. The trays should be alternately
staggered about six inches at the ends to provide easy access of the
fumes to the fruit. As soon as a stack is completed it should be imme-
diately placed in the house for sulfuring. When apricots or peaches
are sufficiently sulfured, the pit cavities will be nearly but not quite
filled with juice, the skins will be loosened from the softened flesh and
the pieces will appear uniformly transluscent, not ' ' raw, ' ' either when
cut transversely or viewed toward the sun.

Pears. — In Lake and Mendocino counties where the highest market
grades of dried pears are produced, the fruit remains in the sulfur
house from 24 to 72 hours, the sulfur being added in batches of 2 to 4
pounds at approximately 8-hour intervals.

In other parts of the state as in Contra Costa County, pears are
usually sulfured less than 24 hours with the result that the dried
product, although of good flavor, is of a light brown color and brings
a lower price.

The larger and greener the pears the longer the time of sulfuring.
When ready for drying the flesh is softened throughout as if cooked
and is white and transluscent while the skin is a light yellow. In order
to prevent drying of the cut surface during sulfuring, pools or pans
of water are used for maintaining a humid atmosphere within the
house.

Grapes and Figs. — These fruits should be placed in the sulfur
fumes while still moist from dipping and left until they acquire the
uniform light yellow color desired.

48

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

DRYING

Apricots and Peaches. — As soon as sulfuring is complete the trays
should be transferred by truck to the dry -yard and spread in the sun-
shine, but never later than 3 or 4 p.m. The trays should be laid
systematically in rows, preferably extending north and south and at
right angles to the tracks. The north side of each tray should rest
on the south edge of the preceding tray. This arrangement economizes
space and by holding all but one edge of the tray off the ground helps
in keeping the trays clean and in picking them up.

Fig. 18. — Scraping dried apricots into lug boxes. Note arrangement
of trays for stack drying.

The fruit should remain exposed to direct sunshine until it is from
a quarter to half dried and has acquired a uniform color. This will
require from 1 to 5 days according to the temperature and air move-
ment. The trays should then be stacked in a staggered pile with the
open ends in the direction of the prevailing winds. After 2 to 6 days
in the stack the fruit will be dry enough for storage. The total drying
time varies greatly with locality and weather conditions but averages 7
days for apricots and 8 days for peaches.

Before the dried fruit from each tray is scraped into lug or sweat
boxes (see fig. 18), discolored pieces, pits or other foreign matter
should be picked out. This important culling can be done much more
efficiently and economically at this point than at any later time. The
dried fruit is then transferred from the dry-yard to the storage
building.

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

49

The ratio of the number of employees required for operating the
cutting shed and dry -yard, exclusive of cutters, to the bearing acreage
was found to average one man to each 8 acres of apricots or each 12
acres of peaches. The cost of this labor (at 40 cents an hour) was
found to average $4.40 for apricots and $4.60 for peaches, per
green ton.

Prunes. — Prunes are placed in the dry-yards in the way described
for apricots and peaches but the trays are not stacked until the prunes
are about three-fourths dried (see fig. 19). This requires from 5 to 10
days in dry weather. During this period large prunes, especially
Imperials and Sugars, should be stirred by hand or a wooden rake.
By turning them over (see fig. 20) and preventing their sticking to
the tray, drying is made more rapid and uniform, and loss from mold
or fermentation minimized.

Fig. 19. — A large prune dry yard.

The trays are then stacked for completion of drying. This requires
one week or longer according to weather conditions. Care must be
taken not to stack prunes until they are at least three-fourths dry or
they may spoil. It is rarely possible to properly dry prunes in less
than 10 days and the average time in favorable weather is two weeks.

Prunes are sufficiently dry when the flesh, especially that around
the pit, has changed to a thick or stiff syrupy condition and clings
tight to the pit. When a handful is squeezed hard, the prunes should
be sufficiently flexible to form a compact mass and yet not soft enough
to stick together when the pressure is released. If some pits are
cracked the kernels should be found dry and shrunken.

There are usually some prunes which do not dry satisfactorily and
form what are popularly referred to as ' ' bloaters, " ' ' frogs, " * ' choco-

50

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

lates," etc. These are the result either of inefficient dipping, or of
immaturity, over-ripeness or partial decay of the prunes. All such
defective prunes should be carefully culled out either during drying
or before the trays are emptied as shown in fig. 21. Failure to do this
will seriously lower the quality of the entire output.

Fig. 20. — Turning prunes to facilitate drying.

Pii

-Sort

(ln<

The average number of dry-yard employees, exclusive of the dip-
ping crew, was found to be one man to each 15 acres of bearing orchard.
The average cost of all dry-yard labor, exclusive of dipping, was found
to be about $2.40 a green ton at a rate of 40 cents an hour.

In case of rain or heavy fog during the drying season, the trays
must all be closely stacked and each stack covered with empty trays,
canvas or a sheet of corrugated iron to prevent the prunes and trays
from getting wet. If the prunes are already partially dried and the

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

51

damp weather is of short duration, no serious damage will result. As
soon as the air is comparatively dry again, the trays should be spread
on the ground to complete the drying. If, as often occurs toward the
latter part of the prune season, weather conditions do not permit of
sun-drying, recourse must be had to dehydraters which at a tempera-
ture of 165° F., which is safe, can economically complete the drying of
the prunes in 24 hours or less without danger of spoiling. In fact,
the economic advantages of modern dehydraters for prunes have
caused many growers to use them exclusively in preference to the
hazardous sun-drying.

Pig. 22. — Drying pears in Lake County. (Note wooden horses for tilting
trays toward south and open sheds for stack drying.)

Pears. — To preserve a light color, pears should be exposed to direct
sunshine for only one-half to two days after sulfuring. In Lake County
the north end of each tray is rested on wooden horses (about 1 to IV2
feet high) to give the pears the maximum sun exposure (see fig. 22).
The trays are next stacked about 20 high, staggered, and with two
1-inch square cross-bars between each pair of trays to afford ample
air circulation for drying. Each stack should be covered with a tray
or other device to shade the top tray and shed rain. In Lake County
permanent open-sided sheds are used to stack the trays under. Two
to four weeks are usually required to complete drying, the trays being
usually restacked two or more times to permit picking out culls and
pears which have dried sufficiently. Rain damage is rare because of
the high sulfur content of the pears and the protection afforded by
stacking and sheds.

52 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

Properly dried pears should be light colored and flat with little
curling of the cut edges. They should not be mushy or puffy in the
center but of a uniform texture similar to soft rubber.

Figs. — Because of variations in the moisture content of figs as
usually picked, it is preferable to sort out and tray only those which
are relatively soft and juicy and place all dried or nearly dried figs in
storage. The length of time which trays of soft figs should be exposed
to direct sunshine will depend on their moisture content and the tem-
perature of the air. In very warm weather the trays of figs need not
be exposed to direct sunshine but preferably allowed to remain stacked.
In cooler weather it is generally necessary to expose the trays for two
or three days before stacking, but care should be taken to prevent
rapid or excessive drying, which results in a tough skin. Stirring the
figs on the trays facilitates even drying.

The interior of a properly dried fig should have the consistency of
a very thick fruit jam or butter and the skin should be soft and
pliable, "like a kid glove." All figs which are split, bird pecked,
moldy, sour or otherwise defective should be culled out before the
figs are placed in sweat boxes for delivery to the packing house.

A simple and fairly satisfactory method of drying Mission figs in
Yolo County is described on page 40.

Grapes. — There are two general methods of producing raisins from
grapes :

1. Drying untreated grapes on trays between the rows in the
vineyard.

2. Drying dipped grapes, with or without sulfur bleaching, on
trays in a dry -yard.

Practically all Muscat raisins and the greater part of the Sultanina
(seedless) raisins are dried in the vineyard, by the first or so-called
"natural" method.

For this method, before the grapes are ripe for picking, a ridge is
thrown up against the south side of every other east and west row of
vines, with a plow or "V" shaped drag. One man and team can
cover about ten acres per day. This operation is referred to as
"V'ing. At this time, the 2'x3' raisin trays are distributed in the
vineyard. This is done at the approximate rate of 3000 trays a day
for each two men and a team. The pickers cut the grapes from two
adjacent rows simultaneously and spread them one bunch deep directly
on the trays which are placed so that one end rests on the ridge which
tilts the trays toward the south. Care should be taken to prevent the
trays from being shaded by the vines, overhanging leaves being clipped
off if necessary.

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

53

After about four days the position of the ends of the trays is often
reversed in order to secure more rapid and uniform drying. For the
same reason, when the grapes on the upper surface of the bunches
have become brown in color and partially shrivelled, the contents of
the trays should be turned over. This is done by two men placing an
empty tray on a filled one, lifting the two together off the ground and
by a quick turn depositing the inverted bunches on the other tray.
Two men can turn about 3000 trays a day.

When all the grapes have developed a uniform brown color and
are from one-half to two-thirds dry, the trays are stacked in piles
20 or more trays high.

The use of paper trays is confined principally to the smaller, more
rapidly drying seedless raisins. The ground between every other pair
of rows should be smoothed by dragging, the papers spread on this
ground and held down by a bunch of grapes until they are filled.
When the raisins are nearly dry enough for stacking, the sides of the
papers are turned in and the papers of raisins made into rolls which
are then stacked like logs of wood.

When the grapes are sufficiently dry to be rolled between the
fingers without exuding moistore, they are emptied from the trays
into sweat boxes which have been previously distributed through the
vineyard. Since each sweat box will hold about 150 pounds, 13 boxes
for each ton of raisins will be required. Two men are able to box
about 5 tons a day. The boxes may be collected at once, or if the
weather permits, may be left in the vineyard. In either case, the
raisins should be left in the boxes several weeks for thorough equaliza-
tion of moisture before delivery to the packing house. After the trays
are emptied they must be collected and removed from the vineyard.

The time required for the several stages in the drying varies con-
siderably with the variety and size of the grapes, the locality, the time
of year and the climate. The figures given in Table 11 will serve as
an approximate guide.

TABLE 11

Approximate Average Time Bequired to Dry Eaisins

Sultanina

Muscat

Turn after

Days

7-8

3-4

7

21

Days
10-12

Stack after

5-7

Box after

7

Deliver after

21

54 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

The production of dried currants from the Black Corinth, a very
small black seedless grape, is the same as for seedless raisins except
that in hot climates like the San Joaquin Valley the best quality is
obtained by drying in the stack without preliminary exposure to direct
sunshine.

The drying of dipped or bleached grapes in a dry-yard is similar
to that of untreated grapes in the vineyard. In drying dipped, but
unsulfured grapes, the bunches should be turned often enough to
prevent molding, and with the same object, the trays should not be
stacked until the raisins are too dry to mold. To obtain a uniform
light amber color in sulfur bleached raisins, they should be exposed
to direct sunshine as short a time as possible — one to four days, accord-
ing to the temperature. After the grapes have acquired a uniform
amber color and are partially shriveled, drying is preferably completed
in the stack.

During seasons of early fall rains, considerable delay and extra
labor is unavoidable in completing the sun-drying of raisins. Occa-
sional light showers will do no damage if the trays are stacked and
covered with an empty tray and when the weather clears, the trays
are spread out again. Paper trays should be rolled and placed under
the vines for protection until they can be spread out again to complete
drying. Raisins which have been wet by rains can be prevented from
molding by covering each stack of trays with a sulfuring hood of
suitable size and shape similar to that shown in fig. 12, and burning
about half a pound of sulfur to each 25 trays as described in Circular
211 of this station. If several hoods are used, the operation becomes
rapid and continuous.

If a long period of rainy weather occurs, recourse must be had to a
dehydrater. While dehydration has not been found economical in the
production of the desired quality of Muscat raisins starting from the
freshly picked grapes, the use of dehydration at the safe temperature
of 160° F., is valuable in rapidly completing the drying of partially
sun-dried raisins during rainy weather. Growers who have "rain
damage" dehydraters for emergency use have been able to save the
cost of such dehydraters in a few years because of the greater yield
and quality of raisins obtained by delaying the picking of the grapes
until they have reached full maturity. Even though not needed every
year, an inexpensive dehydrater is valuable as insurance against
damage or loss to raisins.

In recent years, dehydraters have come into considerable use for
drying soda dipped or sulfur bleached seedless raisins in the Sacra-
mento Valley. If weather permits, the trays are usually spread in

Bull. 388] PRINCIPLES OF SUN-DRYING FRUIT 55

the dry-yard for one day to give the raisins a more uniform color,
after which drying can be quickly, and economically completed in the
dehydrater. For safety, the temperature should not exceed 160° F.,
with dipped, or 150° F., with bleached raisins.

SUMMAEY OF COST OF DRYING

During the survey of dry-yards, on which the information presented
in this bulletin is based, much valuable information on the costs of
picking and drying fruits was obtained. Although not a primary
function of this bulletin, it was thought desirable to summarize the cost
data because of their value as a guide in estimating costs of producing
dried fruits.

As few growers keep itemized accounts of their costs of operation,
it was necessary to calculate average costs from a comparatively small
number of reports. However, all the data used in compiling the follow-
ing tabulations were obtained from exact records kept by experienced
growers and may be considered reliable.

Some of the more important factors which cause variations in costs
of producing dried fruits may be briefly enumerated as follows :

1. Variety of fruit.

2. Size of fruit.

3. Acreage yield.

4. Methods of picking, cutting and drying.

5. Adequacy, efficiency and arrangement of dry -yard and accessory
equipment.

6. Rapidity and uniformity of drying as affected by climatic and
weather conditions.

7. Rates for labor and supplies.

8. Efficiency of labor.

9. Drying ratio of fruit.

Because of these variables, some of which are beyond the control
of the grower, the figures given in the following tables can be con-
sidered only as approximate averages.

Growers will find it very useful to keep a simple account book in
which to record daily the quantity of green and dried fruit handled,
itemized costs of labor and supplies, etc. This information is invaluable
in considering economic improvements in methods or equipment.

56

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

OPERATING COSTS

The costs given in the following tables include, in addition to the
labor cost of picking, all items of labor and supplies required from the
time the fruit is delivered to the dry-yard until the dried product is in
temporary storage awaiting shipment to a packing house. There are
always additional charges for hauling the fresh fruit to the dry -yard
and for hauling the dried product to a packing house which are not
included here because of insufficient data. There are also additional
seasonal charges for labor in washing, repairing and storing trays and
boxes; in care of dry -yard, tracks and other equipment at the begin-
ning and end of the season, etc., which must be prorated among the
total tons of fruit dried during the season. Such items are much less
than the direct costs of handling the fruit but are nevertheless appre-
ciable and should not be lost sight of in compiling the total cost of
production.

TABLE 12

Average Cost or Picking and Drying Apricots (Santa Clara County,
Six Growers, 1921)

Per dry ton*

Picking, @ 37^0 per hour

Cutting, @ lie per 40-lb. box

All other labor, @ 37^c per hour
Sulfur, 7 lbs. @ 5c

Totals

$81.70

Average gross shrinkage 5:1.

TABLE 13

Average Cost of Picking and Drying Peaches (San Joaquin Valley,
Four Growers, 1921)

Picking, @ 42^c per hour

Cutting, @ 8c per 50-lb. box

All other labor, @ 45c per hour
Sulfur, 8^1bs. @5c

Total

$11.32

Per green ton

Per dry ton*

$3.02

$15.10

3.30

16.50

4.58

22.90

.42

2.10

$56.60

Average gross shrinkage 5:1.

Bull. 388]

PRINCIPLES OF SUN-DRYING FRUIT

57

Pears. — Table 14 summarizes data obtained in 1921 at several large
custom dry-yards in Mendocino and Lake counties on the costs of
ripening, cutting and drying pears, with an average shrinkage of 4.3 :1.
The cost does not include picking.

TABLE 14

Average Cost of Drying Pears

Per green ton

Per dry ton

Cutting, @ 15c per box

Labor (all other), @ 40c per hour
Sulfur, @, 4c a pound

Total

$5.10
10.60

.48

$16.18

$21.93

45.58

2.06

$69.57

Prunes. — The figures on the cost of picking and drying prunes,
presented in Table 15, were obtained in 11 dry-yards ranging in size
from small to large and equally distributed between the Santa Clara
and Sacramento valleys. The labor and supplies required for dipping
and drying ranged from $1.60 to $6.15, averaging $4.21 a green ton.

TABLE 15
Average Cost of Picking and Drying Prunes (1921)

Per dry ton51

Picking (by contract)

Dipping, Labor

Supplies (see Table 9).
Drying, Labor @ 373^c per hour

Total

$20.51

* Average shrinkage 2j:l.

Figs. — Data obtained from three experienced Calimyrna fig
growers in the San Joaquin Valley in 1921 showed costs of $20 to $22
per dry ton for picking and drying, of which $8 to $10 per ton was
paid for picking at the rate of 20 cents for each 40- to 50-pound box.

Detailed costs of drying a 120-ton crop of Adriatic figs is presented
in Table 16.

Limited data on the cost of picking and drying Mission figs in the
orchard by the sack method varied from $16 to $20 per dry ton.

58 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

TABLE 16

Cost of Picking and Drying Adriatic Figs
Kearney Park Vineyard — Fresno, 1921.

Per dry ton

Picking, @ 14c per 46-lb. box $8.16

Labor, dipping and drying, @ 40c per hour 13.07

Salt, 19 lbs. @ Mc 14

Sulfur, 13 lbs. @ 4c 52

Power, 14.5 K.W.H. @ 2^c. (For operation of dipper) 36

Total $22.25

Raisins. — Itemized costs of all the operations involved in raisin
drying were not obtained but records obtained in 1919 and 1920 from
several efficiently operated raisin vineyards in the San Joaquin Valley
gave costs closely approximating $9 per green ton, which, on an average
drying ratio of 3% :1, is equivalent to $31.50 per ton of finished raisins.
This cost includes all labor and teams used in preparing the ground,
distributing trays and boxes to and from the vineyard, picking, turn-
ing, stacking and boxing, but not hauling to the packing house. Since
that time the cost of picking and traying has been reduced about one-
third which makes present costs about $7 per green ton or $24 per
dry ton. An additional charge of 1 cent per tray and 5 cents per
sweat box should be allowed for annual repairs.

FIXED CHAEGES

Any consideration of the total cost of drying fruits would be
incomplete without reference to the annual fixed charges on the equip-
ment required. Many growers neglect to include this important item
in calculating costs of production. The investment in each of the
following items of equipment should be recorded.

1. Area of land reserved for dry -yard.

2. Buildings used for cutting, dipping, sulfuring and storing fruits.

3. Lug boxes, trays and sweat boxes.

4. Cars and tracks.

5. Accessory equipment such as dippers, graders, tables, etc.

In general, there are five charges properly made against the
investment represented by this equipment. These are interest, depre-
ciation, upkeep, insurance and taxes. Interest is usually calculated at
a rate of 5% on the current investment. Depreciation and upkeep

BULL. 3S8] PRINCIPLES OF SUN-DRYING FRUIT 59

together will vary from 5% to 15% according to the nature of the
equipment, its use and manner of construction. For instance, dry-yard
land would presumably suffer no depreciation, while trays and boxes
often require an annual depreciation charge of 10% or more. Insur-
ance on combustible buildings and equipment is frequently carried at
rates averaging 2% to 3% of their value. Taxes are variable but
will rarely exceed 3% on an assessed valuation equal to 50% of the
investment (1%% on the market value).

Taking into" consideration the entire equipment, including land, an
annual fixed charge of about 15% to 20% is usually sufficient to cover
all the above-mentioned items. However, each grower should care-
fully determine his own proper allowance for fixed charges. This
should then be divided by the number of tons of fruit dried during
the year and added to the previously recorded direct cost of labor and
materials used in drying the fruit.

Fixed charges per ton vary rather widely, the chief factors of
difference being : first, the amount and nature of equipment used and,
second, the tonnage dried in any given year. Sufficient exact data on
fixed charges from which to compile reliable averages was not obtained.
However, the following tables are presented as guides in tabulating
equipment costs and prorating fixed charges thereon.

Apricots. — The investment in apricot drying equipment given in
Table 17, has been calculated from data furnished by W. R. Kingston
of Ventura County. The figures are for equipment capable of drying
100 tons (fresh weight) of apricots per season. Assuming an annual
fixed charge of 15% on a total investment of $2253, there would be a
fixed charge of $3.38 per fresh ton, which on a drying ratio of 5 :1
would equal $16.90 per dry ton. No charge is made for dry -yard land,
it being assumed that before the drying season some annual crop of
sufficient value can be harvested from the land to at least cover the
interest on the value of the land in addition to the cost of production.

Similar data furnished by Martin J. Madison of the California
Prune and Apricot Growers' Association, for a plant capable of drying
300 fresh tons of apricots per season, is summarized in Table 18.

Prunes.- — Data obtained from four prune growers in Santa Clara
County with an annual production of 70, 165, 190 and 1500 fresh tons,
respectively, gave fixed charges of $3.64, $2.60, $4.24 and $3.23 per
fresh ton, respectively. With an average drying ratio of 21/4 :1, the
above figures represent an average fixed charge of $7.70 per ton of
dried prunes.

60 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION

TABLE 17

Investment in Apricot Drying Equipment
(After W. R. Kingston, Ventura County)

Cost per
Equipment for 100 fresh tons per season. fresh ton

300—50 pound picking boxes at 36c $1.08

1200—3' x 8' trays at $1.05 12.60

Cutting shed, 1000 square feet area at 20c 2.00

Pitting tables, knives and pans 1.00

8-tray cars at $12.25 98

1-transfer car at $21.00 21

475 feet of track at 35c *. 1.66

6 sulfur houses at $25.00 1.50

Storage bin, 5' x 15' x 15' at $150.00 1.50

Total investment per fresh ton $22.53

Fixed charge per fresh ton at 15% 3.38

Fixed charge per dry ton at 15% 16.90

TABLE 18

Investment in Apricot Drying Equipment

(After M. J. Madison, San ,)ose)

Cost per
Equipment for 300 fresh tons per season. fresh ton

1000—50 pound picking boxes at 253^c $ .85

6000—3' x 8' trays at 70c 14.00

Cutting shed, 36' x 94' 2. 58

Pitting tables, knives and pans 33

17 tray cars at $10.00 57

2 transfer cars at $12.50 08

2 turntables at $12.50 08

1500 feet of track with rails, ties and spikes 78

15 sulfur houses at $33.00 1. 65

Warehouse— 36' x 60' 4.00

7 hand trucks and 1 platform scale 77

Total investment per fresh ton $25.69

Fixed charge per fresh ton at 15% 3.85

Fixed charge per dry ton at 15% 19.25

STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION

BULLETINS

No. No.

253. Irrigation and Soil Conditions in the 352.
Sierra Nevada Foothills, California.

261. Melaxuma of the Walnut, "Juglans 353.

regia." 354.

262. Citrus Diseases of Florida and Cuba 357.

Compared with Those of California.

263. Size Grades for Ripe Olives.

268. Growing and Grafting Olive Seedlings. 358.
273. Preliminary Report on Kearney Vine-
yard Experimental Drain. 359.

275. The Cultivation of Belladonna in Cali- 361.

fornia.

276. The Pomegranate. 362.

277. Sudan Grass 363.

278. Grain Sorghums.

279. Irrigation of Rice in California. 364.

280. Irrigation of Alfalfa in the Sacramento

Valley. 366.

283. The Olive Insects of California.

285. The Milk Goat in California. 367.

286. Commercial Fertilizers.

294. Bean Culture in California. 368.
304. A Study of the Effects of Freezes on

Citrus in California. 369.

310. Plum Pollination. 370.

312. Mariout Barley. 371.

313. Pruning Young Deciduous Fruit Trees.

319. Caprifigs and Caprification. 372.

324. Storage of Perishable Fruit at Freezing

Temperatures. 374.

325. Rice Irrigation Measurements and Ex-

periments in Sacramento Valley,
1914-1919. 375.

328. Prune Growing in California.

331. Phylloxera-Resistant Stocks. 376.

334. Preliminary Volume Tables for Second-

Growth Redwood. 377.

335. Cocoanut Meal as a Feed for Dairy 379.

Cows and Other Livestock. 380.

339. The Relative Cost of Making Logs from

Small and Large Timber. 381.

340. Control of the Pocket Gopher in Cali-

fornia. 382.

343. Cheese Pests and Their Control.

344. Cold Storage as an Aid to the Market- 383.

ing of Plums.

346. Almond Pollination. 384.

347. The Control of Red Spiders in Decidu-

ous Orchards.

348. Pruning Young Olive Trees. 385.

349. A Study of Sidedraft and Tractor 386.

Hitches.

350. Agriculture in Cut-over Redwood Lands. 387.

Further Experiments in Plum Pollina-
tion.

Bovine Infectious Abortion.

Results of Rice Experiments in 1922.

A Self-mixing Dusting Machine for
Applying Dry Insecticides and
Fungicides.

Black Measles, Water Berries, and
Related Vine Troubles.

Fruit Beverage Investigations.

Preliminary Yield Tables for Second
Growth Redwood.

Dust and the Tractor Engine.

The Pruning of Citrus Trees in Cali-
fornia.

Fungicidal Dusts for the Control of
Bunt.

Turkish Tobacco Culture, Curing and
Marketing.

Methods of Harvesting and Irrigation
in Relation to Mouldy Walnuts.

Bacterial Decomposition of Olives dur-
ing Pickling.

Comparison of Woods for Butter Boxes.

Browning of Yellow Newtown Apples.

The Relative Cost of Yarding Small
and Large Timber.

The Cost of Producing Market Milk and
Butterfat on 246 California Dairies.

A Survey of Orchard Practices in the
Citrus Industry of Southern Cali-
fornia.

Results of Rice Experiments at Cor-
tena, 1923.

Sun-Drying and Dehydration of Wal-
nuts.

The Cold Storage of Pears.

Walnut Culture in California.

Growth of Eucalyptus in California
Plantations.

Growing and Handling Asparagus
Crowns.

Pumping for Drainage in the San
Joaquin Valley, California.

Monilia Blossom Blight (Brown Rot)
of Apricot.

A Study of the Relative Values of Cer-
tain Succulent Feeds and Alfalfa Meal
as Sourses of Vitamin A for Poultry.

Pollination of the Sweet Cherry.

Pruning Bearing Deciduous Fruit
Trees.

Fig Smut.

CIRCULARS

No.

87. Alfalfa.
113. Correspondence Courses in Agriculture.
117. The Selection and Cost of a Small

Pumping Plant.
127. House Fumigation.
129. The Control of Citrus Insects.
136. Melilotus indica as a Green-Manure

Crop for California.
144. Oidium or Powdery Mildew of the Vine.

151. Feeding and Management of Hogs.

152. Some Observations on the Bulk Hand-

ling of Grain in California.
154. Irrigation Practice in Growing Small
Fruit in California.

No.

155. Bovine Tuberculosis.

157. Control of the Pear Scab.

160. Lettuce Growing in California.

161. Potatoes in California.

164. Small Fruit Culture in California.

165. Fundamentals of Sugar Beet Culture

under California Conditions.

166. The County Farm Bureau.

167. Feeding Stuffs of Minor Importance.
170. Fertilizing California Soils for the 1918

Crop.
173. The Construction of the Wood-Hoop

Silo.
178. The Packing of Apples in California.

CIRCULARS — {Continued)

No.
179.

184.
190.
199.
202.

203.
208.

209.
210.
212.
214.

215.
217.

220.
228.
231.
232.

233.
234.

235.

236.

237.

238.
239.

240.

241.

244.
245.
247.
248.

249.
250.

Factors of Importance in Producing

Milk of Low Bacterial Count.
A Flock of Sheep on the Farm.
Agriculture Clubs in California.
Onion Growing in California.
County Organizations for Rural Fire

Control.
Peat as a Manure Substitute.
Summary of the Annual Reports of the

Farm Advisors of California.
The Function of the Farm Bureau.
Suggestions to the Settler in California.
Salvaging Rain-Damaged Prunes.
Seed Treatment for the Prevention of

Cereal Smuts.
Feeding Dairy Cows in California.
Methods for Marketing Vegetables in

California.
Unfermented Fruit Juices.
Vineyard Irrigation in Arid Climates.
The Home Vineyard.
Harvesting and Handling California

Cherries for Eastern Shipment.
Artificial Incubation.
Winter Injury to Young Walnut Trees

during 1921-22.
Soil Analysis and Soil and Plant Inter-
relations.

The Common Hawks and Owls of Cali-
fornia from the Standpoint of the

Rancher.
Directions for the Tanning and Dress-

of Furs.
The Apricot in California.
Harvesting and Handling Apricots and

Plums for Eastern Shipment.
Harvesting and Handling Pears for

Eastern Shipment.
Harvesting and Handling Peaches for

Eastern Shipment.
Marmalade Juice and Jelly Juice from

Citrus Fruits.
Central Wire Bracing for Fruit Trees.
Vine Pruning Systems.
Colonization and Rural Development.
Some Common Errors in Vine Pruning

and Their Remedies.
Replacing Missing Vines.
Measurement of Irrigation Water on

the Farm.

No.

251. Recommendations Concerning the Com-

mon Diseases and Parasites of
Poultry in California.

252. Supports for Vines.

253. Vineyard Plans.

254. The Use of Artificial Light to Increase

Winter Egg Production.

255. Leguminous Plants as Organic Fertil-

izer in California Agriculture.

256. The Control of Wild Morning Glory.

257. The Small-Seeded Horse Bean.

258. Thinning Deciduous Fruits.

259. Pear By-products.

260. A Selected List of References Relating

to Irrigation in California.

261. Sewing Grain Sacks.

262. Cabbage Growing in California.

263. Tomato Production in California.

264. Preliminary Essentials to Bovine Tuber-

culosis Control.

265. Plant Disease and Pest Control.

266. Analyzing the Citrus Orchard by Means

of Simple Tree Records.

267. The Tendency of Tractors to Rise in

Front; Causes and Remedies.

268. Inexpensive Lavor-saving Poultry Ap-

pliances.

269. An Orchard Brush Burner.

270. A Farm Septic Tank.

271. Brooding Chicks Artificially.

272. California Farm Tenancy and Methods

of Leasing.

273. Saving the Gophered Citrus Tree.

275. Marketable California Decorative

Greens.

276. Home Canning.

277. Head, Cane, and Cordon Pruning of

Vines.

278. Olive Pickling in Mediterranean Coun-

tries.

279. The Preparation and Refining of Olive

Oil in Southern Europe.

281. The Results of a Survey to Determine

the Cost of Producing Beef in Cali-
fornia.

282. Prevention of Insect Attack on Stored

Grain.

283. Fertilizing Citrus Trees in California.

284. The Almond in California.

The publications listed above may be had by addressing

College of Agriculture,

University of California,

Berkeley, California.

20m-6,'25