Date Development,

Handling, and Packing

in the United States

Agriculture Handbook No, 482

C/3

Agricultural Research Service

UNITED STATES DEPARTMENT OF AGRICULTURE

;.„ o
Date Development, Handling, and

Packing in the United States

by G. L. Rygg

Agriculture Handbook No. 482

Agricultural Research Service

UNITED STATES DEPARTMENT OF AGRICULTURE

USDA, National Agricultural iMraxy

NALBIdg

10301 Baltimore Blvd

Beltsvifle, MD 20705-2351

Washington, D.C. Issued November 1975

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402 - Price 85 cents

Stock Number 001-000-03428-6

Catalog Number A1.76:482
Pesticides used improperly can be injurious to man, animals, and

plants. Follow the directions and heed all precautions on the

labels.

Store pesticides in original containers under lock and key—out of

the reach of children and animals—and away from food and feed.

Apply pesticides so that they do not endanger humans, livestock,

crops, beneficial insects, fish, and wildlife. Do not apply pesticides when there is danger of drift, when honey bees or other

pollinating insects are visiting plants, or in ways that may

contaminate water or leave illegal residues.

Avoid prolonged inhalation of pesticide sprays or dusts; wear

protective clothing and equipment if specified on the container.

If your hands become contaminated with a pesticide, do not eat

or drink until you have washed. In case a pesticide is swallowed

or gets in the eyes, follow the first aid treatment given on the

label, and get prompt medical attention. If a pesticide is spilled

on your skin or clothings remove clothing immediately and wash

skin thoroughly.

Do not clean spray equipment or dump excess spray material

near ponds, streams, or wells. Because it is difficult to remove all

traces of herbicides from equipment, do not use the same

equipment for insecticides or fungicides that you use for herbicides.

Dispose of empty pesticide containers promptly. Have them

buried at a sanitary land-fill dump, or crush and bury them in a

level, isolated place.

NOTE: Some States have restrictions on the use of certain

pesticides. Check your State and local regulations. Also, because

registrations of pesticides are under constant review by the

Federal Environmental Protection Agency, consult your county

agricultural agent or State Extension specialist to be sure the

intended use is still registered.
PREFACE

Since commercial date growing was established in the United

States early in the 20th century, a large amount of experimental

work on handling and storing dates has been done by private

operators and by government and university personnel. Most of

the results of. this voluminous work have been published in

various outlets. The purpose of this handbook is to bring together in one concise publication the pertinent, available information on the subject together with previously unpublished

material and applicable information from other date-growing

areas of the world.

Methods of handling dates from harvest to retail marketing

are constantly changing. Some of the methods that are described

have been discontinued, either because they were superseded by

more desirable methods, or because dates are no longer grown

where the methods were used. Some changes were adopted

because the product is improved; others were forced by economic

necessity. The description of the discontinued methods may be

useful in guiding others in their practices as they initiate a dategrowing industry in new areas.

ACKNOWLEDGMENT

All photographs are reproduced through the courtesy of the

Date Administrative Committee, Indio, Calif.

USDA policy does not permit discrimination because of race,

color, national origin, sex, or religion. Any person who believes he or she has been discriminated against in any USDArelated activity should write immediately to the Secretary of

Agriculture, Washington, D.C. 20250.

Ill
CONTENTS

Page

Introduction 1

Stages of date development 2

Physical and chemical changes in growing dates 3

Physical and chemical changes associated with ripening,

and the composition of ripe dates 5

Inorganic constituents of ripe dates 7

Enzymes in dates 8

Composition of seeds of ripe dates 10

Maturity at harvest 10

Factors that influence time of harvest 12

Frequency of picking 14

Mechanical harvesting I5

Unpollinated Deglet Noor dates 20

Handling at the packinghouse 21

Fumigation 21

Cleaning , 22

Sorting . 23

Grading 24

Artificial maturation 25

Dehydration 28

Hydration 3Q

Pitting _ 34

Pasteurization 34

Surface coating 35

Blemishes , 3g

Blacknose ^ 3g

Black scald 3g

Puffiness or skin separation 3g

Respiration 3Y

Plant sanitation 3g

Forms of deterioration 3g

Pathological 3g

Nonpathological ^ 3g

Packaging _ ^j

Storage 43

Transportation 4^

Literature cited 4g

IV
Date Development, Handling, and

Packaging in the United States

By G. L. RYGG,» plant physiologist,

Agricultural Research Service, Western Region, Riverside, Calif.

INTRODUCTION

Dates have been used as a staple food for several thousand

years (69)J^ Their high energy value and good storability make

dates a wise choice of crop in places where they can be grown.

About three-fourths of the dry matter in dates is sugar. Few ripe

dates have any starch. They contain small amounts of vitamins

A, Bi, and B2, and substantial amounts of nicotinic acid, but

none of the other vitamins is present in significant amounts.

Dates are a good source of iron and potassium, and a fair source

of calcium, chlorine, copper, magnesium, and sulfur, and they

contain a small amount of phosphorus {9, 11, 3U, S5, 78, 8Uy 102),

Sixteen kinds of free amino acids have been identified {80),

Most of the sugar in ripe, dry, and semidry cultivars of dates is

usually sucrose; the remainder is invert sugar, a mixture of

equal parts of glucose and fructose. All or nearly all the sugar in

most ripe, soft cultivars is invert sugar. The general relationship

between the texture of date flesh and the predominant kind of

sugar has been known since Henry B. Slade did his pioneering

work in the first decade of the 20th century {105, 113). The

general association of dry-textured cultivars and high sucrose

content does not appear to be causally related, however, as

several dry-textured cultivars have very little sucrose. Examples of such cultivars are Ashrazi, Dayri, Fursi, Menakher,

Zahidi, and Azmashi {17).

Dates pass through several well-defined stages during their

growth and ripening. Long {^9) recognized seven periods in the

life of the fruit; the last of these covered ripening and curing.

* Retired.

2 Italic numbers in parentheses refer to Literature Cited, p. 48.
2 AGRICULTUHE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

Vinson {11JÍ) and Haas and Bliss {35) recognized two stages based

on fruit development, the first being one of growth and the

second one of sugar accumulation. Ripening would constitute a

third period. Vinson's first stage may be divided into two parts,

making a total of three stages in addition to ripening {8^), These

are determined by compositional changes in the fruit and are

related to the color changes as described below.

STAGES OF DATE DEVELOPMENT

American date growers are accustomed to using the Arabic

terms in referring to the stages of development of dates. For this

reason, these terms are used to designate the various stages in

this report.

**Kimri^* refers to young, green-colored dates. The kimri stage

may be divided into two phases. The first is characterized by

rapid increase in size and weight, rapid accumulation of reducing sugars, low but increasing rate of accumulation of total

sugars (especially sucrose), high active acidity, and high moisture content. The second phase is characterized by a reduced

rate of gain in size and weight, greatly reduced rate of gain in

reducing sugars, considerable reduction in the already low rate

of gain in total sugars, slightly reduced active acidity, and a

moisture content slightly higher than that in the first phase {SU),

The kimri stage continues until the dates begin to change from

green to the characteristic color ofthe "khalal" stage. The khalal

stage corresponds to the second stage of Vinson and of Haas and

Bliss, the third of Rygg, and the sixth of Long. Dates in the

khalal stage may be yellow, pink, red,- or scarlet, or yellow

spotted with red, depending upon cultivar. The rate of gain in

size and weight continues to decrease, the weight may even

decrease slightly, invert sugar accumulates slowly but sucrose

accumulates at a rapidly increasing rate, active acidity decreases, and moisture content decreases in both percentage and

in quantity per fruit.

The **rutab'' stage follows the khalal and encompasses the

ripening period as understood in the United States. According to

Dowson and Aten (22), this term means **wet," This stage begins

when the fruit begins to soften and merges into the final "tamar"

stage. Little or no sugar accumulates during the rutab stage.

Dates continue to lose water but not enough to make them selfpreserving.

Dates in the tamar stage have dried to a rainy nrm consist-
DATE DEVELOPMENT IN THE UNITED STATES á

ency, and the sugar-to-water relationship is such that the dates

are not subject to fermentation.

"Hababauk," a term not commonly used in the United States,

refers to the earliest stage of development of the date fruit. The

color at this stage is cream to faint green U^). This stage is

usually included in the kimri stage in American usage.

PHYSICAL AND CHEMICAL CHANGES IN

GROWING DATES

Young date fruits contain as much as 85 percent or more

water up to the time they have attained nearly full size. Invert

sugar constitutes from 40 to 97 percent of the total sugar in the

very early stages of growth and remains high during the main

period of growth (5, 8U)* Invert sugar decreases rapidly in

percentage as sucrose accumulates after the fruit has attained

approximately full size. No other sugar, even in minute quantity, has been detected in dates. As dates ai)proach full development, sucrose usually constitutes above 80 percent of the sugar

present. This is true for soft as well as for semidry and dry kinds.

Table 1 gives the proportion of sucrose in the Deglet Noor

(semidry) and Barhee (soft) dates at representative periods as

they grow and ripen. Some cultivars of soft dates have a smaller

proportion of sucrose prior to ripening; for example, in KhadTABLE 1.—Percentage ofsucrose in total sugar in Deglet Noor

and Barhee dates at various stages of development^

Stage of Deglet

Date maturity Noor Barhee

Percent Percent

May 17 Kimri 59 __

May 23 „do._ -- 23

June 14 -.do.. 17 __

June 21 .-do.. — 12

July 19 -.do__ 16 _^

July 21 -do.. __ 8

Aug. 23 Khalal 76 ._

Sept. 2 ._do_- 78

Sept. 11 ..dc- „ 80

Sept. 11 Rutab .- .3

Sept. 13 Khalal 83 ._

Sept. 13 Rutab 71 -

^ Adapted from Rygg i^Jf).
4 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

rawy only 30 to 40 percent of the sugar is sucrose {JÍ3), in the

Zagloul 57 percent {3\ and in the Hayany about 73 percent {ZÉ),

A small amount of starch appears in young dates for a short

time after pollination {US), but this soon disappears in most

cultivars. The Samaani cultivar in the United Arab Republic,

however, is reported to have 12.8 percent starch (dry weight

basis) in the green kimri stage and 3.1 percent in the ripe rutab

stage U).

Fiber increases in quantity per fruit but decreases on percentage basis as the fruit grows {lU, 8i).

Pectic materials increase in quantity per fruit until ripening

begins. The amount of protopectin reaches its maximum when

the fruit attains full size, but soluble pectin increases slowly

until ripening begins {8^),

Tannin and tanninlike compounds reach a maximum concentration in late May or early June, while the dates are still small

and green, and gradually decrease on a percentage basis (110).

Maier and others (5Í, 57, 59) found that much of the substrate

that is involved in enzymic browning in ripe Deglet Noor dates is

a hitherto undescribed compound, which they called dacylifric

acid, along with the isomers neodactylifric and isodactylifric

acids.

Acidity in dates is highest during the period of most rapid

growth. It decreases in the latter part of the growing season and

continues to decrease as the fruit ripens {8U)-

Date development is influenced by cultural i^ctors, and by

environmental factors, some of which may occur early in the

growing season but tlie effects of which may not be detected

until coîisiderably later. Heat units accumulated by the end of

April may largely determine the earliness of harvest {19), Halawy palms deprived of water in June and July bear an abnormally high proportion of dates with hard ends and khalal

shrivel, and they have a heavy immature shatter. Palms deprived of water later in the summer are less affected {^9), Date

palhfis tolerate a fairly high salt concentration in the soil,

apparently largely because of their ability to exclude the salt

{SO), Heavy nitrogen fertilization increases yield but lowers

quality (Jé?). Heavy loads of fruit on the bunches reduce the size

of the fruit but may not lower the quality {SI), High atmospheric

moisture shortly before the dates ripen may cause shrivel in the

Maktoom variety {Al), Prolonged high temperatures in the

spring may adversely affect Deglet Noor date development in a

way that does not become noticeable until the dates ripen {91,

92), This effect is discussed in greater detail on page 6.
DATE DEVELOPMENT IN THE UNITED STATES 5

PHYSICAL AND CHEMICAL CHANGES

ASSOCIATED WITH RIPENING, AND THE

COMPOSITION OF RIPE DATES

Pronounced changes, both physical and chemical, occur in

dates as they ripen. The surface changes from the characteristic

khalal color to another color, also characteristic of the cultivar,

usually amber or brown, but sometimes black. Along with the

change in color is a change in texture from crisp to soft and

yielding. A fßw cultivars, including dry-textured ones such as

Thoory an(î lienta, do not become soft at this stage. They remain

hard, but instead of being crisp they become chewy or brittle,

depending on moisture content. As ripening progresses in the

more common cujtivars moisture is lost and the skin becomes

more or less wrinkled.

Just before the onset of ripening, from 80 to 85 percent of the

total sugar in Deglet Noor dates is sucrose or cane sugar; the

remainder is invert sugar. During ripening, some of the sucrose

is hydroly?ed into invert sugar, and, in ripe fruit, sucrose

usually constitutes from 60 to 80 percent of the total sugar. A

number of factors influence the amount hydrolyzed during

ripening. Cultural treatments during the growing season, and

the temperature, humidity, and rainfall during ripening undoubtedly influence the amount of hydrolysis (^8, 29, 84, 108),

In many invert sugar cultivars, the proportion of each kind of

sugar just before ripening is similar to that of Deglet Noor at

the same stage (W, US, UU)- All or nearly all the sucrose of the

soft or invert sugar cultivars is converted into invert sugar

during ripening, whereas in the Deglet Noor only a small part of

the surose is converted. The basis of the difference in sucrose

hydrolysis in the two types is found in the state of the sugarsplitting enzyme invertase {113), Table 1 shows the marked

difference in sucrose hydrolysis in these two types of dates as

they ripen.

Although starch is not usually found in ripening or ripe dates,

other acid-hydrolysable polysaccharides occur in small quantitites. These materials do not diminish during ripening {8^)-

Some of the insoluble pectic substances are converted into

soluble pectin in the course of ripening, and the amount of total

pectic substances decreases (<^^).

F^ts and waxes in the dates have received little attention.

Hilgeman and Smith U^) found that the ether extract of the skin

of ripe dates constituted from 2.52 to 7.42 percent of the skin.
6 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

The amount of ether extract in the skin of cultivars of soft dates

was inversely related to susceptibility to lo3s from moisture

damage, but Degtet Noor dates were high in crude fat content

and were also highly susceptible to moisture damage,

^ The edible portion of Halawy dates grown in Iraq contains 1.90

percent fat or ether extract (IS), Chatfield and Adams (11) give

an average value of 0.6 percent fat in the edible portion.

The wax in ripe Deglet Noor has at least two fractions. The

major fraction melts at about 183** F (84° C) and the minor

fraction, at about 160*^ F (71"* O (8¿),

The acidity of dates usually decreases (that is, the pH rises)

when they ripen. The pH of the Deglet Noor may rise from about

5.3 to 5.6 to about 6.0 to 6.4. The pH of the flesh of ripe fruit

varies greatly, however, depending upon the quality. A high pH

value is characteristic of dates of high quality. An overall range

in ripe Deglet Noor from 3.9 to 6.8 has been observed, but most

fruits of this cultivar fall within the rangefrom pH 5*3 to 6.3 (87).

The pH of invert sugar cultivars is in tjie same general range

as the Deglet Noor. Occasional values as high as 7.2 have been

foynd (S, 99).

High temperatures in the early part of the growing season,

April and May, have been associated with the development of

dry-textured ripe fruit in the Deglet N<>or. The fruit of this

cultivar appears to be particularly sensitive to high temperatures at that time but rapidly acquires tolerance to heat about

the first of June, Rapid cell division characterizes the fruit

development at that time. The young seeds seem to be the most

tender part of the fruit (Pi, 92). Dates that are injured by high

spring temperatures are more acid than normal when they ripen

and are more difficult to hydrate. These differences become

noticeable only after the dates ripen (87).

The suddenness of the onset of hot weather during the heatsensitive period may influence the degree of injury. Yarwood

(118) has demonstrated that some plants exposed to moderately

high temperatures for several short periods can develop a certain degree of heat tolerance.

Soft cultivars are not subject to the kind of heat injury

described for Deglet Noor, but Nixon (n) has shown that skin

separation in ripe dates may be increased by high temperatures

or high humidity or both during the early part of the growing

season.

One of the conspicuous changes in composition associated with

date ripening is the conversion of the bitter soluble tannin into

insoluble, tasteless forms. The nature of the precipitating reac-
DATE DEVELOPMENT IN THE UNITED STATES 7

tion is not known but is thought to be similar to that occurring

in the tanning of leather. If this comparison is correct, the

tannin combines with protein to form an insoluble product {ZU,

68, 8Jf, 113, Hi), The immature khalal stage of some cultivars,

including Barhee and Braim, contains so little tannin that they

are only slightly, if any, astringent.

Polyphenols (tannin and tanninlike substances) constitute

about 3 percent of the dry weight of date flesh (58), Three

polyphenols make up about 98 percent of the total amount of this

group; the remaining 2 percent consists of at least 10 constituents.

The moisture content of dates decreases as the fruit ripens.

Deglet Noor fruit drop from 66 to 50 percent moisture during the

khalal stage (that is, fruit in the red stage between the green

kimri and amber rutab stages). Ripe fruit of this cultivar usually

contain less than 30 percent moisture (SJ^) and are generally

harvested in the United States when the moisture gets below 20

percent. The climatic conditions during ripening will modify

these values somewhat.

Similar decreases in moisture content occur in the other

cultivars as they mature, but ripe fruit of the soft kinds usually

contain more mositure, some having 40 percent or more. The

high moisture content of ripe fruit constitutes the basis of one of

the major operations in preparing the soft cultivars for the

market, that of reducing the moisture to a percentage that

permits the dates to be marketed with a minimum of spoilage.

Inorganic Constituents of Ripe Dates

The mineral content of dates does not change materially as

the fruit ripens, but the amount present is nutritionally significant. Haas (3i) analyzed six cultivars—ivhadrawy, Halawy, Deglet Noor, Zahidi, Kustawy, and Barhee. Khadrawy and Halawy

had a slightly higher mineral content than the other cultivars

analyzed, but the overall range was 2,14 to 3.38 percent ash.

Potassium constituted from 41 to 44 percent of the total ash.

Other minerals were calcium, 2 to 4 percent; magnesium, 2 to 3

percent; sodium, 8 to 12 percent; and inorganic phosphorus, 4 to

13 percent. Minor inorganic elements were iron, 5 to 26 parts per

million (p/m); manganese, 2 to 4 p/m; and copper, 3 to 6 p/m.

Copper was measured only in the Deglet Noor. The high potassium to sodium ratio is of dietetic significance for people who

must restrict their intake of sodium.
8 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

Enzymes in Dates

Invertase has been studied more than any other enzyme in

dates. Investigators chose this enzyme because of the ease with

which its activities are followed. They assumed that conditions

that favored invertase activity would also be likely to favor the

activity of other enzymes. Vinson (ii^)divided the invertase into

endoinvertase and ektoinvertase according to whether it was

attached to the cell constituents or was free to escape into the

surrounding liquid when the cells were broken. Its most noticeable activity is to convert sucrose into glucose and fructose. In

soft cultivars, this conversion is carried to completion or near

completion, but in most semidry and dry types only a portion of

the sucrose is hydrolyzed. Its activity is promoted by high

moisture content and a warm temperature.

Hasegawa and Smolensky (39) have recently added significantly to the information on invertase and its activity in dates.

Green dates contain fairly large amounts of insoluble invertase

(called endoinvertase by Vinson {113% and practically no soluble

invertase (called ektoinvertase by Vinson). As the dates turn

red, the insoluble invertase is reduced to about one-half its

former amount, as expressed in units per.date fruit, and remains

fairly constant as the fruit continues to mature.

Soluble invertase, as found by Hasegawa and Smolensky {39),

increased from about 3 percent of the total invertase in green

dates to a maximum of about 75 percent of the total in the late

red stage and then decreased slightly as the fruit matured. In

the meantime, the total invertase activity in the Deglet Noor

fruit they used increased from 5 units per date to about 12.4

units. They suggested that the sharp increase in invertase

activity is the prime reasan for the increase in reducing sugar

that accompanies maturation and ripening rather than a loss of

membrane system integrity.

The relative invertase activity in dates of various qualities

appears in table 2 by Hasegawa and Smolensky {39),

The invertase activity is stable at temperatures below 104° F

(40° C), about 50 percent activity is lost by heating at 122° F

(50° C) for 10 minutes, and 90 percent is lost by heating at 149° F

(65° C) for 10 minutes {39).

Peroxidase occurs in dates, but its function is not known. It is

not involved in the reactions associated with darkening. The

optimum acidity is pH 4.7 {79). It is moré tolerant to heat than

both invertase and polyphenolase {59, 79), High concentrations of
DATE DEVELOPMENT IN THE UNITED STATES

TABLE 2.—Comparison ofinvertase activity in four different

qualities of dates (39)

Activity (units/date)^

Grades Insoluble Soluble Total

Natural

Waxy

No. 1 dry

No. 2 dry

2.27b (2.87b)

2.19b (2.88b)

2.00b (3.03b)

1.50a (2.54a)

8.61c (10.9c)

8.96c (n.9,)

6.43b ( 9.7b)

4.90a ( 8.3a)

10.88 (13.77)

11.15 (14.78)

8.43 (12.73)

6.40 (10.84)

^ Values with common subscript letters within a column are not statistically

different at the 0.05 probability level. Activity expressed as units per 10 g dry

weight is shown in parentheses.

sucrose greatly inhibit the activity, but dextrose has little or no

effect (79).

Polyphenolase is responsible for the enzymatic oxidative portion of date darkening. It is more sensitive than peroxidase to

acid but is more tolerant to alkalinity. Its optimum acidity is pH

5.0. Its tolerance to heat is intermediate between that of invertase and that of peroxidase (59, 60, 79),

Polygalacturonase (PG), one of the pectic enzymes, was studied by Hasegawa and others (38). Its activity was nearly absent

in Deglet Noor dates in the green stage, but increased as

maturity progressed. Most of the enzyme was formed or activated in the late red stage with the peak acitvity occurring when

the fruit began to soften. That the activity is related to the

softening process is evident by the fact that they found 20 times

higher activity in the softened apical end than in the still hard

basal end of half-soft fruit.

In relating PG activity to maturity, Hasegawa and others (S8)

found the following amounts at the various maturities: Green,

trace; early red, 0.18; late red, 2.3; 50 percent soft, 2.5; 100

percent soft, 2.5; and soft-ripe, 0.81. The values are units per gram

dry weight.

PG activity in the several grades of dates was: Natural, 1.68

units per gram dry weight with relative activity of 100; waxy,

1.39 units and 83 relative activity; No. 1 dry, 1.17 units and 70

relative activity; and No. 2 dry, 1.06 units and 63 relative

activity. The lower PG activities were associated with the drier

and harder grades of dates, but the significance of this association is not yet clear.

Dates undoubtedly contain additional enzymes, but data on

their characteristics are not available.
10 AGRICULTURE HANDBOOK 482, U.S. DEFT. OF AGRICULTURE

Composition of Seeds of Ripe Dates

Interest in the compositian of date seeds stems from their

possible use in livestock feed. The compositional data on these

seeds, reported by varions workers, vary tremendously. In their

summary of composition of various foods, Chatfield and Adams

(11% list the following values for date seeds: Water, 17.0 percent;

crude protein, 1.0 percent; crude fat, 0.5 percent; crude fiber, 2.1

percent; ash, 1.6 perceiit; and total carbohydrates, 65,6 percent.

The total of these values is 88.7 percent; the nature of the

remaining material is not stated. Other reports give crude

protein values as high as 6.9 percent (107); crude fat, 9.0 percent

(107); crude fiber, 23 percent (1); and a&h, 3.1 percent (2), Total

carbohydrates or nitrogen-free extract values range from 23.0

percent (10) to 72.7 percent (by difference) (107), The carbohydrates in date seeds are largely in the form of hemicellulose,

which is readily converted to dextrose by acid or enzyme hydrolysis (22). Date seeds contain 1,9 p/m estrone (-40),

Dowson and Aten (22) gave the following additional information

on date pit composition:

Percent

Moisture 6.46, 7.7

Oils ___ . 8.49, 8.8

Proteins l_ 5.22

Carbohydrates 62.51

Fibers _ 16.2O

Ash 1,12

The fatty acids consisted of the following fractions:

Percent

Capric acid , 0.7

Caprinic acid ^ 5

Laurie acid 24.2

Myristic acid 9.3

Palmitic acid 9.9

Oleic and linoleic acids 52.2

Stearic aeid _. 3.2

The fatty acids constituted 1.3 percent of the oil; the iodine

number was 56.3. They also listed a number of characteristics of

the date pit oil.

MATURITY AT HARVEST

Several factors must be taken into account to determine how

well matured the dates should be when harvested. The capacity
DATE DEVELOPMENT IN THE UNITED STATES 11

of the fruit to develop good quality during aritificial ripening

and maturation determines the minimum maturity. Considerations that govern the desirability and advisability of early

harvesting include: (1) Effect upon total yield; (2) need for

earliest possible harvest to minimize loss from unfavorable

weather, especially rain, and from insect infestation; (3) desirability of early marketing of as much of the crop as possible; (4)

relative cost of all aspects of handling and placing on the market

dates picked at different stages of maturity; (5) market preference as to type of date (for example, hydrated versus nonhydrated); (6) availability of pickers; and (7) amount and kind of

hydrating and drying equipment available at the packinghouse

(18, 20, 67, 97),

The unequal ripening of fruits on a bunch historically required that each fruit be picked individually in all but the dry

cultivars if the best possible quality was to be retained. Current

economic and labor conditions dictate that the number of harvests be held to a minimum.

In the cultivars such as the Deglet Noor, there is more

uniformity within a given bunch than between bunches. Therefore, it has become the accepted practice to harvest this cultivar

by the bunch whether harvest is by machine or by hand. For

economic reasons, all bunches in an orchard are often harvested

in one operation. However, better quality fruit is obtained if

bunches are harvested selectively as they ripen. At least two

separate harvests are desirable—one near the middle of the

season, and the other near the end.

The stage of development at which dates have accumulated

the maximum sugar per fruit differs somewhat among cultivars.

In the Deglet Noor, this stage appears to be at the time

softening has progressed about one-half the distance from the

tip to the base of the fruit; whereas, in the Barhee, the sugar

influx is complete when the first translucent spot associated

with normal ripening appears {8U). In the Maktoom, sugar

accumulation is practically complete when 15 percent of the

surface has become translucent; however, in the Khadrawy

sugar may continue to accumulate until the fruit is soft ripe, full

rutab (i, U2). The total yield obviously increases as long as the

amount of sugar and other dry matter per fruit continues to

increase, barring loss from rain, insect damage, disease, or other

causes.

The Deglet Noor should not be harvested before the turning

stage in which the texture is yielding to pliable and the color is

amber to cinnamon. Fruit of this variety has a better storage
12 AGRICULTURE HANDBOOK 482, U.S. &EPT. OF AGRICULTURE

potential if harvested when it has a reádish or lavender ring at

the perianth end than if it is allowed to remain on the palm until

this ring has faded with more advanced maturity (8,108),

Halawy should reach the soft ripe stage, but Maktoom can be

ripened into an acceptable product if harvested when 10 to 25

percent of the surface is translucent U^>. A given variety may be

harvested at a less advanced maturity in the latter part of the

harvest season than at the beginning. Sugar content alone can

not be used as an index of harvest maturity because other

factors not directly associated with sugar content—such as

texture^ aroma, flavor, and appearance^-Kîontribute to the overall quality.

Deglet Noor dates that must be harvested before the optimum

stage of maturity has been reached attain better texture and

flavor if the bunches are cut and hung under a shelter until the

fruit ripens than ifthe dates are stripped from the bunches while

much of the fruit is in the khalal stage and ripening is completed

on trays. Moderate warming during finalripening helps improve

date quality. The longer one can defer bunch cutting or stripping,

up to the time nearly all the dates are ripe, the higher average

quality and yield are likely to be (89).

Factors That Influence Time of Harvest

The need for harvesting as early as possible is determined

largely by the likelihood of rain during the normal harvest

season. The los&from tearing and cracking of the fruit and from

the activity of micro-organisms under those conditions may

become exceedingly heavy. The threat of rain varies considerably in the different date-growing areas, and local experience

will determine how much consideration it must be given.

Insect infestion in the unharvested fruit varies from year to

year and may be an incentive to early harvesting because the

infestation may increase with increasing maturity and with

damage from rain. This infestation may be reduced by dusting

tbe punches with insecticides at appropriate times before and

during the early stages of ripening (28, W* Growers must be

careful to comply with legal regulations governing the use of

pesticides. Visible pesticides residues are removed at the packinghouse before tlie dates are marketed.

The cost of grading tJates that have suffered rain damage or

insect infestation is higher than it would otherwise be, and the

accuracy is lowered because of hidden damage that can be

detected only upon cutting the fruit. The need for occasional
DATE DEVELOPMENT IN THE UNITED STATES 13

regrading adds to the cost per pound of handling the salable

fruit.

The increased cost of handling dates harvested before full

maturity tends to offset the advantages of early harvest. Dates

harvested before they are ripe must be processed to complete the

ripening that otherwise proceeds on the palm. They also must be

dehydrated enough to reduce the moisture content to a reasonable, safe level unless the dates are to be marketed through low

temperature channels such as frozen food outlets.

The amount of shrinkage from dehydration can be determined

from figure 1 (85), Early in the khalal stage, Deglet Noor dates

may have a moisture content of about 66 percent, but this value

decreases to about 60 percent later in the season (^-4). This

cultivar is generally harvested when the moisture content has

dropped to 20 percent or less.

In addition to normal shrinkage from moisture loss, the processing of immature fruit entails varying amounts of loss from

spoilage resulting from the activity of yeasts, molds, and bacteria. The cost of processing Deglet Noor dates picked prematurely

is so great that immature, moist fruit is often graded as culls to

avoid the expense of completing ripening and dehydration.

70

(/) 60

CO

o

-I

50

Lu

O

<

40

Z

ÜJ

O

er 30

Lu

CL

20

10

-

^^

- 27%^

;^r -

- 23% 25%-

#

^

-

- 20%-

^

^

X

-

-

yy#

y

-

^Úr

/^

-

yy

c^ -

30 40 50 60

INITIAL MOISTURE CONTENT

IN PERCENTAGE OF FRESH WEIGHT

70

FIGURE 1.—Percentage loss in weight when the moisture content is reduced

from the initial value to a fínal value of 20, 23, 25, and 27 percent.
14 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

Market preference may influence harvest matxirity within

certain Hmits. This influence is more likely to be felt in the

Deglet Noor and other semidry cultivara than in the soft ones. If

the preference is for hydrated dates, it may be desirable to delay

harvest until the dates are fairly dry. Because the tendency for

the Deglet Noor to dry on the palms differs greatly from year to

year, the need for hydration is influenced materially by the

climate of the season as well as the wishes of the handlers and

consumers.

The availability of pickers and the pay they receive indirectly

affects the maturity of dates at harvest. When pickers are

plentiful and relatively inexpensive, picking can be made at

short intervals and the fruit can be picked at near optimum

maturity. Conversely, when pickers are scarce and costly, the

intervals between picking are lengthened, and increasing portions ofthe^îrops dry beyond the best textiire and consistency.

Packinghouse operators establish requirements of maturity of

fruit brought in according to thç equipment available for handling slightly immature fruit, and according to the capacity of

the house in relation to the rate at which fruit is received.

Houses designed primarily to handle the Deglet Noor are usually well equipped to handle large quantities of dry dates that

require hydration; whereas, the capacity for maturation and

dehydration is not so great. Dates in need of maturation and

dehydration must i)e attended to without delay, but dry dates

may be hydrated when convenient.

Frequency ofPicking

Diy or "Bread''Kinds

Di^ types of dates are grown on a very limited scale in the

United States. Thoory and Kenta are two of the most important

dry cultivars. These cultivars are usually allowed to ripen fully

on the palm, are very dry and hard when picked, and are usually

harvested in one picking.

Seinidry Kinds

The Deglet Noor cultivar is the most popular in the United

States. These palms were formerly picked as many as seven

times a season. With changes in handling methods, market

demands, increasing costs, and decreasing availability of pickers,

the number of pickings has been reduced to one or two. The

reduced number of pickings decreases the proportion of dates

harvested as naturals but improves handling and processing.
DATE DEVELOPMENT IN THE UNITED STATES 15

The principal consequence of reducing the number of pickings

is to increase the proportion of dates in the dry categories (73, 7U,

89), This may constitute an economic advantage, as dry dates

are more stable, less perishable, and more easily handled than

the softer, more moist dates. On the other hand, the dry dates

have lost some of the delicate flavor and aroma that they

contained at the optimum stage of ripeness.

The lowest number of pickings that can be made without

undue sacrifice of yield and quality is determined to some extent

by the climatic characteristics of the season. The drier the

harvest season the lower the number of pickings that can be

tolerated. In years with a less dry harvest season, whether

because of rain or because of high humidity with little or no rain,

more pickings with shorter intervals between pickings must be

made to reduce losses from rotting, fermentation, and insect

infestation to a practical minimum.

Soft Kinds

The frequency of picking soft kinds of dates is governed by

cultivar as well as by climatic and economic factors. The firmer

kinds are often harvested in two pickings by allowing dates that

ripen first to remain on the palm until half or more are ripe and

then picking the ripe ones. The remaining dates are picked when

all or nearly all are ripe.

The softer, more moist kinds must be picked soon after they

start to ripen to avoid heavy losses from fermentation and insect

infestation, Cultivars of this kind include the Hayany, Tárbarzal,

and Sphinx.

The customary procedure for harvesting dates has been for

pickers to ascend the palms with buckets or other containers and

handpiók the dates into the container as illustrated in figure 2.

Mechanical Harvesting^

In recent years, mechanical aids to havesting have been

developed. Illustrations depicting equipment used to a considerable extent in the Coachella Valley appear in figures 3 to 6.

The adoption of mechanical harvesting aids (76) necessitates

changes in handling procedures at the packinghouses. Entire

bunches are necessarily harvested at one time, but all the

bunches on each palm tree need not be harvested at one time.

Variations in time of maturity among the bunches require more

3 Portions of this section were revised or updated by P. F. Burkner, agricultural engineer, USDA, ARS, Riverside, Calif., to reflect changes in the industry

since original preparation of the manuscript.
16 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

PN^382

FIGURE 2.—Dates being harvested in the traditional manner by picking

individual dates into a bucket. Soft kinds are picked in this manner, but

shallow containers are used to avoid crushing the tender fruit.
DATE DEVELOPMENT IN THE UNITED STATES 17

than one passage through the garden by the harvesting crew.

Only the drier kinds are suited to mechanical harvesting. The

softer kinds are too tender and would be damaged.

Mechanical harvesting of the Deglet Noor cultivar has been

used commercially since 1963. Currently, over 80 percent of this

cultivar, which constitutes 90 percent of U.S. production, is

PN^283

FIGURE 3.—Date bunches are severed from the palms by a man positioned in

the fruiting area. The bunches drop into a large container.
18 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

harvested mechanically. With machines, 25 men can harvest as

much fruit as 100 hand pickers.

The basic mechanical harvesting system consists of selectively

harvesting by bunches and then removing the fruit with a

mechanical shaker. The dates are then handled and stored in 20-

inch-deep bulk bins containing about 750 pounds of fruit.

Several experimental mechanical harvesting systems were

tried before a commercially acceptable system was developed.

PN-4384

FIGURE 4.—The container with the date biinches has been lowered to a

hopper containing a shaking device for removing the dates from the

bunches; the dates drop into a bin underneath.
DATE DEVELOPMENT IN THE UNITED STATES 19

PN-4385

FlGDBE 5.—Filled containers being removed and readied for hauling to the

packinghouse.

These systems varied in the method pickers were positioned in

the tree and how the fruit was shaken off the bunch.

The harvesting system adopted by the industry uses a truckmounted telescopic boom to position a worker in a basket near

the bunches. This worker cuts mature bunches and places them

in the basket. The basket and man are then lowered to a shaker

trailer drawn by the boom truck. Here, the fruit is mechanically

shaken from the bunches and flows into bulk bins. Three men

operate the system: One truck driver-boom operator, one bunch

cutter, and one shaker operator.

Mechanical harvesting compared with the same number of

pickings made by hand shows no effect on the quality of the

product (72). In this comparison, all the fruit was removed from

the harvested bunches, but two pickings were made by each

method.

The depth of dates in a bin is limited by the moisture content

ofthe wettest ripe dates, and probably should not exceed 15 to 18

inches (96). Unripe dates should not be allowed to drop into these
20 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

containers. These dates ripen on standing and, having a high

moisture content, will be crushed, and the released sirup will

make the neighboring dates sticky.

PN-4386

FIGURE 6.—Filled bins at the packinghouse awaiting handling procedures.

UnpoUinated Deglet Noor Dates

Deglet Noor dates sometimes grow to nearly full size even

though they are not pollinated. Such dates are seedless or have

only rudimentary pieces of hard material. In years when this

kind of date is abundant, growers and packers are tempted to try

to realize some income from them by ripening and drying them

and using them in products. When used for this purpose, all

fragments of seedlike tissue must be removed.

These dates, if left on the palm until they have ripened or at

least started to ripen, can be utilized in products by completing

the ripening and maturation in a packinghouse and drying to

the required moisture content as determined by the use intended.
DATE DEVELOPMENT IN THE UNITED STATES 21

The economic feasibility of this practice may be questioned,

however, because of the cost of preparing this material, which

will bring a relatively low return per pound, and because of the

high shrinkage, especially if the dates are picked in the khalal

stage of maturity as is often done. The percentage loss in weight

can be determined from figure 1. The initial moisture content is

likely to be more than 40 percent and may be nearly 70 percent

(85).

HANDLING AT THE PACKINGHOUSE

The first step in handling dates on arrival at the packinghouse

is determined by the organization of the house. Samples are

commonly taken and classified immediately after the load is

weighed. The returns paid to the grower are based upon the

gradeout of the samples. The bulk of the fruit loses its identity

as it passes through the packinghouse. Sampling is not necessary in houses that provide custom grading and packing because

each grower's fruit retains its identity until it leaves the house.

Fumigation

Dates are fumigated as soon as possible after they are picked

to arrest all forms of insect life. Specially constructed rooms are

required for this process for they must be as nearly gastight as

possible. The impervious layer of the walls, ceiling, and floor

should be as near the inner surface as possible to avoid the

exposure of porous materials to the fumigating gas. Linings of

sheet metal with soldered joints are excellent. A suitable gas

barrier consists of two or more layers of strong building paper

composed of two sheets laminated by a heavy layer of asphalt.

The seams must be lapped and cemented. The paper may be

protected with a covering of wallboard or lumber. Masonry walls

are usually porous and need to be sealed with dense plaster or

with hot asphalt or asphalt emulsion. The floors must be gastight, and care must be taken to form a seal at the junction of

the walls with the floor. The doors must be fitted with gastight

gaskets. Two doors are commonly provided in opposite walls so

that fruit may be introduced through one from the outside and

the fumigated fruit withdrawn from the other into the packinghouse, thus minimizing the opportunity for reinfestation.

Provisions must be made for circulating and distributing the

fumigating gas and for exhausting the gas to the outdoors.

Facilities for heating the rooms should be provided for use in
22 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

the cooler part of the year because the fruit should be fumigated

at a temperature of 6(r F (16° C) or higher.

A recent development consists of fumigating dates in bins or

field boxes stacked outdoors and covered with heavy plastic

sheeting. This procedure permits refumigation as often as

needed while awaiting processing and packing for shipment.

Methyl bromide is the most commonly used fumigating gas.

Instructions for its use, suitable concentrations, and applicators

to aid in the application of suitable dosages are available from

the manufacturers. Methyl bromide is a very poisonous gas, and

its odorless nature requires that it be handled with utmost

caution. Carbon disulfide, hydrocyanic acid, and ethylene oxide

have also been used for fumigation (£1, 108, 115). Current

regulations should be consulted before the fumigant is chosen.

Temperatures of 40° F (4° C) or lower prevent insect activity

but do not kill all forms of insect life. Temperatures considerably

below 32° F (0° C) are required to effect a complete kill.

The mushroom mite (Tyrophagus lintaeri Osborn) sometimes

attacks stored dates. Its small size and ability to survive long

periods of drying and absence of food make complete control

difficult (108).

Cleaning

For many years, dates were cleaned by passing them over

damp toweling attached to sloping mechanical shakers or placed

inside sloping revolving cylinders. Dust and coarse foreign matter were removed by passing the dates over a coarse screen and

suction before they reached the toweling. Frequent towel

changes and the use of germicides on them were helpful in

maintaining a low microbial population.

In more recent years, washers have been used for cleaning

dates. Loose foreign matter is removed by passing the dates over

slats before they reach the washer. The washer may have

revolving brushes moistened with water and detergent, or the

cleaning may be accomplished with jets of water and detergent.

In either method, the detergent is removed with a water rinse.

Experience has shown that recirculating the washing solution is

undesirable because of the buildup of micro-organisms. Washers

depending upon brushes for their cleaning action cannot be used

on soft cultivars, but spray jets give good results (111, 112),

Figure 7 shows one of the large bins used with the mechanical

aid being dumped at the beginning of the passage of dates

through the packinghouse.
DATE DEVELOPMENT IN THE UNITED STATES 23

PN-4387

FIGURE 7.—Dates being dumped from the large bin to start the packinghouse

operations.

Various devices have been used to remove the excess water

after washing. Dates that are too moist are trayed and held in

dehydrating rooms; dry dates are usually taken directly to the

hydrator. The excess surface water on dates that are packaged

immediately after washing and grading is removed by passing

them on a conveyor under a blast of air.

Sorting

Immediately after they are cleaned, the dates are sorted to

remove culls and to separate the remaining fruit into uniform

lots. The first sorting operation produces fairly broad classes

based largely on maturity and texture. Subsequent sorting

separates these classes into several lots, each of which is uniform in color, texture, size, and moisture content. This procedure

is necessary with Deglet Noor but is often dispensed with for

soft cultivars. Dates that are too moist are placed in single

layers in shallow trays with wire mesh bottoms and transferred

to drying rooms where any necessary maturation is accomplished and the excess moisture removed. Those that are too dry

and firm are taken to hydrating rooms where the tissue is
24 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

softened, and moisture is added by methods described under the

sections on hydrating and canning.

Dates are mechanically separated into several sizes. Hand

sorting is required to separate dates into categories based on

texture, blemishes, and various properties that make them unfit

for human use (culls) (fig. 8).

Grading

The U.S. Department of Agriculture (USDA) grades of dates

are based on color, uniformity of size, absence of defects, and

character. Sugar content is not closely related to grade. Dates of

all commercial grades may have approximately the same total

sugar content, but the dry grades of such cultivars as Deglet

Noor are likely to have more sucrose and less reducing sugar

than the moist dates of desirable texture {H, 87, lOU).

A detailed description of date grades may be found in the

latest revision of "United States Standards for Grades of Dates,"

FIGURE 8.—Dates are separated by hand into several groups according to

moisture, color, texture, and appearance.
DATE DEVELOPMENT IN THE UNITED STATES 25

copies of which are available from Processed Products Standardization and Inspection Branch, Fruit and Vegetable Division,

Agricultural Marketing Service, U.S. Dept. of Agriculture, Washington, D.C.20250.

Most American date packinghouses have USDA inspectors on

continuous duty during operating hours. Inspection covers adherence to grade standards, which include cultivar characteristics; uniformity of color; freedom from insects, diseases, and

various other defects; and uniformity of size for the grade.

Inspection for adherence to size requirements is illustrated in

figure 9.

Artificial Maturation

Deglet Noor

Artificial maturation of Deglet Noor dates is not practiced

extensively in areas well adapted to the culture of this cultivar,

but is employed in marginal areas where the dates do not ripen

properly on the palm or where damage from rain is likely to

occur if the dates are left on the palms until they ripen natuPN-4389

FIGURE 9.—The larger packinghouses have continuous USDA inspection. In

this operation, the date size is checked to assure that the fruit complies

with grade specifications.
26 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

rally. In seasons when the dates are late in ripening, it may

become necessary to complete the process in rooms designed for

the purpose.

Maturation rooms must be provided with means for circulating the air uniformly in all parts of the room and for introducing

fresh air as needed. The temperature and humidity must be

controlled.

Less mature fruit needs higher temperature and higher humidity than more mature fruit, but for the Deglet Noor the

temperature should not exceed 95"" F (35'' C) for best results.

Higher temperatures result in too much darkening and loss of

flavor. Freeman (27), in 1911, suggested maturing this variety at

113° to 118° F (45° to 48° C), but later experience has shown this

temperature to be too high (56).

Other Cultivars

Artificial maturation of soft cultivars is usually accomplished

at temperatures somewhat higher than those used for Deglet

Noor, Temperatures of 95° to 115° F (35° to 46° C) are commonly

used to save time and to complete maturation before the dates

spoil from mold growth or fermentation.

Different cultivars and different lots of each cultivar may

require modifications in the details of the procedure used. Therefore, considerable skill and experience are essential for an

operator to develop a high quality product consistently.

In Arizona, where dates are usually harvested at an earlier

sta^e of maturity than is commonly practiced in California, the

cultivars have been classified into three groups according to

their maturation requirements 0.6).

Group A includes the Khadrawy, Kustawy, Hayany, Sayer,

Khalasa, and Sphinx. Dates in this group are matured at 104° to

110° F (40° to 43° C) for best results. Temperatures up to 130° F

(54° C) may be used^ but some of the cultivars become too dark,

and some ofthe enzymatic processes associated with maturation

are interfered with and the final quality is lowered. Maturation

is complete when the fruit has lost its translucency and little or

no hard tissue remains. This should not require more than 18 to

24 hours.

Group B consists of Halawy, Dayri, Deglet Noor, and Zahidi.

These cultivars are more fibrous than those in group A and

require more time for maturation, 2 to 4 days or more. A safe

temperature is 95° to 100° F (35° to 38° C), but instead of removing water as in group A, it is often necessary to add water to

dates in group B. Usually, this may be accomplished by maintaining a relative humidity (RH) of 80 to 90 percent, but some-
DATE DEVELOPMENT IN THE UNITED STATES 27

times the "sweat box technique'' is required. This process consists of placing the fruit in lug boxes lined with wrapping paper

and covering the contents with the same paper. The lugs are

stacked in a room held at 95° to 100° F (35° to 38° C), and 70 to 80

percent RH. Dry and hard dates, especially Zahidi, need to be

sprinkled at intervals.

Group C consists of Iteema, Maktoom, and Saidy. Because of

the heavy, thick tissue and the late ripening, these cultivars are

matured at 113° to 115° F (45° to 46° C) and 70 percent RH. Even

at this high temperature, 2 to 4 days or longer is required to

complete the process.

The procedures described above are at best only outlines upon

which to base the practice of artificial maturation. The operator

must change and modify the conditions and determine the

length of treatment for each lot of fruit. The importance of his

judgment has been expressed aptly by Hyde in *Trocessing

Arizona Dates" {U6y p. 10):

Since the character of the fruit entering the maturation rooms changes from week to week during the

harvest and from season to season, no hard and fast

rules can be established. Successful maturation can

never be reduced to a science; it is an art to be

mastered only after years of close observation and

never-ceasing attention to detail. When the processor

can manipulate the temperatures, the air movements,

the humidity, and the time so that his dates have a

light golden amber for Iteema, Khadrawi and Maktoom, and a deep shining black for Hayany and Sphinx;

when the skin is thin, soft, pliable with no trace of crust

or shell; when the fruit tissue is uniform, devoid of

fibre, and melts in the mouth like a soft fresh chocolate

cream; when the rag around the pit has been reduced

to a mellow pulp; when the rather timid flavoring

esters remain unchanged or unmasked; when a processor can accomplish these things, then he will have

"arrived."

Chemical Aids to Ripening

Numerous chemicals have been tried to hasten date ripening

and to improve the quality of the final product. A few have given

sufficiently favorable results to encourage their use for a time,

but all were eventually abandoned in the United States because

naturally ripened dates were better and less labor and shrinkage were involved.

Vinson {113) observed the effect of more than 100 chemicals on
28 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

date maturation, and found that several hastened the process.

The most promising of these was acetic acid. Freeman (27) used

ammonia experimentally to some extent but devoted more time

to incubation at various controlled temperatures and humidities.

Other compounds that have found limited favor for a short

time include carbon dioxide, ethylene, hot lye, and salt (21, 2i, UU,

66).

Gibberellin applied to young dates has given unfavorable

results. When applied to Deglet Noor dates within a few weeks

after the spathe opened, it increased shrivel prior to ripening

and increased the susceptibility of the fruit to checking and

blacknose. When applied to half-grown dates, gibberellin prevented the dates from developing a full khalal color and slightly

delayed ripening (70),

Freezing to Promote Ripening

Completely turgid, immature dates (khalal) may be ripened

into an edible, although not an especially high quality product, if

they are first frozen (^i, 62, 89, 109), This treatment removes the

astringency by converting the soluble tannin into an insoluble

form; it also develops the translucent appearance of a normally

ripened date, but the flavor is not equal to that of fruit that has

been permitted to ripen naturally, and the high initial moisture

content introduces a high but unavoidable shrinkage.

Dehydration

A sizable portion of the crop of both semidry- and soft-date

types must be freed from excess moisture before it can be

marketed unless it is to be consumed immediately or stored at

very low temperatures. This drying is accomplished in specially

constructed rooms similar to those used for maturation, and the

two processes are often accomplished simultaneously. Provision

must be made for thorough circulation of the air, for frequent

changes to remove the moisture, and for heating.

Dates are spread in a single layer in shallow wire mesh trays.

Stacks of trays are stowed in a manner that will allow good air

circulation. To avoid too rapid drying and the development of

hard brittle skin, the relative humidity should not be permitted

to fall much below 50 percent unless fairly short cycles of

alternate dry and more humid air are used in blowing air across

the fruit. This is accomplished by recirculating air until a fairly

high humidity is built up and then introducing fresh preheated

air at a very low humidity. With Deglet Noor, a temperature of

85° to 90° F (29° to 32° G) is desirable. The dehydration process
DATE DEVELOPMENT IN THE UNITED STATES 29

may take from 3 to 8 days depending on the condition of the fruit

and the time of year (18),

The amount of drying required depends on the objective of the

operator. A desirable moisture content for Deglet Noor in California is from 23 to 25 percent. Fruit with this moisture content

has a desirable soft texture and is dry enough to store well

without being unduly subject to molding, fermenting, darkening,

and loss of flavor (8). In soft cultivars, the usual practice in

California is to reduce the moisture content to 25 to 28 percent.

In Arizona, a moisture content from 25 to 30 percent is used for

dates entering the usual commercial channels through refrigerated warehouses. Dates intended for shipment directly from cold

storage, for immediate consumption soon after packing, are

allowed to have a moisture content of about 35 percent.

A practice used on a small scale in California consists of

placing soft cultivars of dates, with moisture contents of 30 to 40

percent, in storage at OT (-18''C) immediately after cleaning

and within 1 day of harvesting. Such dates are kept at a low

temperature until they are sold. Consumer acceptance has been

satisfactory, but this method has not been exploited extensively.

Dates harvested during and soon after wet weather present a

special problem in drying. These should be placed on wire mesh

trays and held in cold storage with good air circulation while

awaiting regular packinghouse handling procedures (119). Spoilage in such dates has been reduced materially by dusting them

with sulfur before they are picked (117). The sulfur presents a

cleaning problem, but modern cleaning equipment should aid in

its removal.

Since moisture control is one of the most important phases of

date handling, a quick and easy method for measuring moisture

is desirable. Such a method, with sufficient accuracy for the

needs, is found in the small hand refractometer. These refractometers are made for two ranges of soluble solids contents, the

low range extending from 0 to 60 percent solids (40 to 100

percent moisture) and the high range, from 45 to 85 percent

solids (15 to 55 percent moisture). The high range instrument is

needed for use with dates.

A paste is prepared from the flesh and applied to the ground

glass surface in the instrument. The percentage of soluble solids

is read from a scale that is calibrated in percentage of sugar.

The reading must be given a suitable correction for temperature

and an additional correction for insoluble solids. The latter

correction differs with cultivar. Corrections for some of the

commonly grown cultivars are; Deglet Noor and Dayri, -1.4;

Zahidi, -1.3; Khadrawy and Halawy, -1.2; Saidy, -1.1; Medjool,
30 AGRICULTURE HANDBOOK 482, U.S. DEFT. OF AGRICULTURE

-1.0; Maktoom, -0.7; and Barhee, -0.3 (83), These values are

subtracted from the moisture content found after the temperature correction has been applied to the percentage of soluble

solids as read on the instrument.

More accurate results are to be had by drying to constant

weight the ground date tissue in thin layers under vacuum at

149^ to 158*" F (65° to 70° C), but this method is much more time

consuming and requires rather expensive equipment; furthermore, the equipment is not portable as is the refractometer.

An important advantage of the refractometer method is the

small size of sample needed. The moisture content of single

fruits can readily be measured. A good practice is to measure the

maisture content of individual dates that are representative of

the wettest and the driest in a lot to determine the uniformity of

grading. A uniform moisture content is important. An occasional

very moist date in a package may ferment and cause the entire

package to be unacceptable. Moisture contents of dates in a

package do not equalize rapidly, and moist dates may spoil

before the moisture content of these dates is reduced to the

average of the remaining dates in the package even though a

fungicide may have been used in the package.

Hydration

The purpose of hydration is basically to soften the texture of

the fruit. This may be accomplished by simply incorporating

additional water in the flesh or it may be necessary to break

down the fibrous tissues; a combination of these two processes is

often necessary.

Dates, especially of the soft cultivars, which have become too

dry and hard as a result of remaining on the palms too long after

they were ripe or from being kept in a dry atmosphere too long,

can be softened readily by increasing the moisture content.

The need for hydration in the Deglet Noor may be great or

small according to the climate of the season, cultural practices of

the grower, the soil on which the dates were grown, and the

frequency of picking the ripe fruit. Dates that have dried too

much from too long exposure to dry air are readily softened if

they are otherwise of good quality. Dates that are hard and dry,

because of the nature of the climate during the growing season

or because of the soil on which they were grown, are more

difficult to soften because of the necessity of breaking down the

fibrous flesh. These dates are more acid than those which soften

on the palm as they ripen, and the more acid the tissue the more
DATE DEVELOPMENT IN THE UNITED STATES 31

difficult it is to soften by hydration. Deglet Noor fruit with a pH

value of 5.5 or lower soften with considerable difficulty, and the

product is of low quality. Rubbery dates have low pH values and

can not be hydrated satisfactorily {90, 91),

Almost all Zahidi dates require hydration. Fortunately, however, this cultivar responds quite readily to the treatment.

In California, the most commonly used hydration procedure

consists of traying the dates and exposing them to live steam.

The time and temperture required are governed by the condition

of the fruit to be hydrated. The length of the treatment can be

reduced by raising the temperature, but the quality of the

product is likely to suffer. A common treatment for Deglet Noor

dates is to introduce live steam at 5 psi until the temperature

reaches 140° F (60° C) and to maintain it for 4 to 8 hours. For this

purpose, small, well-insulated rooms with forced air circulation

are used so that the temperature and humidity may be uniform

and accurately controlled to bring the warm moist air equally to

all the dates. The doors may remain closed after the steam

supply is turned off, or the dates may be moved to another tight

room where they are allowed to cool slowly in the moist air to

increase the moisture absorption and tissue softening. The

operator needs considerable skill to obtain the best results.

Dates to be hydrated are spread on mesh-bottom trays one to

two dates deep, as shown in figure 10. A stack of such trays

ready to be trucked into a hydrating chamber appears in figure

11.

The conditions used for hydrating and softening Deglet Noor

dates in Algeria, the original home of this cultivar, are somewhat different from those used in California. In that country,

the temperature used is somewhat higher, 149° to 158° F (65° to

70° C), the humidity is lower (55 percent RH), and the duration

shorter (2 to 4 hours) {97), Deglet Noor dates grown in Algeria,

especially in the vicinity of Biskra and Tolga, may be less

difficult to soften than those grown near Indio, Calif., because of

the lower prevailing temperatures in April and May, and possibly in September {98),

Moderately dry dates and those not too high in acid may be

hydrated or softened without heating above room temperature

by exposing them to a partial vacuum while immersed in water.

A return to atmospheric pressure forces water into the flesh.

Such dates, on standing several days at room temperature or

under refrigeration, attain a desirable texture. If the treatment

is properly executed, the dates will not become too soft and

sirupy. Dates that require more severe treatment may be soft-
32 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

ened by utilizing a combination of the vacuum and the steam

treatments. The reduced exposure to heat compared with steam

hydration alone improves flavor retention.

The "sweat box technique," described in the section "Artificial

Maturation," is a form of hydration.

In addition to softening the dates, steam hydration tends to

improve the keeping quality over that of nonhydrated dates with

similar moisture content as a result of killing a high proportion

of the micro-organisms on and in the fruit (99).

Not all the chemical changes brought about by hydration have

been ascertained. In dates that contain appreciable quantities of

sucrose, hydrolysis of some of this sucrose has been noted (7, 27),

but this change probably is not entirely responsible for the great

change in texture. Other hydrolytic changes affecting the structural components of the fruit no doubt occur, but data on the

PN^390

FIGURE 10.—Dry dates are trayed before introduction into the hydration

chambers. The paddle wheel at the rear smooths the dates on the meshbottom trays and removes the excess.
DATE DEVELOPMENT IN THE UNITED STATES 33

PN-4391

FIGURE 1 !•—Stack of trays on a handtruck about to be placed in a hydrating

nature or extent of these changes are not available. Maier and

Metzler (52) suggested that soft-textured, low moisture Deglet

Noor dates may be produced by adding moisture and perhaps

invertase and holding at about 140° F (60° C), long enough to

produce the desired hydrolytic reactions, and then cooling and

removing the excess moisture. Former practices were designed

to hold sucrose inversion to a minimum to retain as much as

possible of the peculiar quality of Deglet Noor dates. Coggins

and others (15) have studied the chemical and histological

changes that accompany softening.

Acidity in dates changes very little during hydration unless

neutralizing agents are deliberately introduced. Alkaline ammonium sulfite added to the water to be infiltrated into the dates

by partial evacuation improves the quality of the product when

the dates to be treated are moderately acid. The ammonium
34 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

hydroxide used in this treatment decreases the acidity, and the

sulfite prevents excessive darkening (95). No commercial use has

been made of this method of neutralizing the acid.

Pitting

Increasing proportions of dates are pitted before they are

offered for sale. Eighty percent or more of the Deglet Noor dates

packed by the California Date Growers' Association in 1970 was

pitted for greater consumer convenience and to avoid paying the

transportation of the pit, which constitutes about 10 percent of

the weight of a whole date. Figure 12 shows a bank of 12

mechanical pitters.

Pasteurization

Pasteurization is intended to kill all forms of micro-organisms

and insects in dates. In actual practice, the insect mortality is

complete, but not all micro-organisms (spores) are killed. In 1916,

Forbes (26) used this treatment successfully to kill all forms of

PN-4392

FIGURE 12.—A bank of 12 mechanical pitters.
DATE DEVELOPMENT IN THE UNITED STATES 35

insect life by holding the dates at 149° F (65° C) 2 to 4 hours.

Clague and Fellers (12) recommended a temperature of at least

loi*' F (66° C) for 1 hour at 100 percent RH. At higher temperatures, one may use shorter periods and lower humidities.

A room used for pasteurization must be well insulated and

equipped with heating facilities of sufficient capacity to heat a

charge of dates rapidly, and the air must be circulated rapidly to

obtain uniform heating. Provision should be made for introducing fresh filtered air.

Maturation and drying should be completed before the dates

are pasteurized because the temperatures used tend to destroy

some of the enzymes whose activities promote maturation, and

sirup exudes from dates that have more than about 35 percent

moisture. Pasteurizing dates that have a high moisture content

does not consistently give good results as they sometimes mold

or ferment in spite of the treatment (43). Hilgeman and Smith

(4,8) failed to kill all fungi and bacteria in dates held 1 hour at

176° F (80° C) or 2 to 4 hours at 158° F (70° C).

In Arizona, dates are pasturized by raising the fruit temperature to 150° F (66° C) and holding for 30 minutes. To do this, the

air temperature needs to be raised to about 162° F (72° C). With

good equipment, about 1 hour is needed to bring the dates to the

required temperature. More severe conditions than these accomplish a higher percentage of kill, but they are objectionable

because they produce excessive darkening and loss of flavor and

make the dates less attractive (4S, 46, 63). Pasteurization is not

commonly practiced in California except incidentally during

steam hydration.

Sharpies (101) found that pasteurization at a fruit surface

temperature of 165° F (75° C) for 30 minutes sometimes reduced

the bacterial population by perhaps 75 percent and sometimes

slightly or not at all. Fumigation with ethylene oxide likewise

reduced the bacterial population only slightly. Both pasteurization and fumigation reduced the yeast population, but neither

reduced the mold population enough to effect a reliable prevention of spoilage from this cause. Dates thus treated are therefore

likely to contain enough viable molds and bacteria to spoil the

fruit when a suitable environment is provided. Dark dates

appeared to be more prone to spoil from microbial action than

light-colored ones of the same cultivar and moisture content.

Surface Coating

Many materials have been used to coat dates to reduce

stickiness and enhance the appearance. A spray composed of 2
36 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

percent butylated hydroxyanisole, 2 percent butylated hydroxytoluene, 6 percent vegetable oil, and 90 percent,water, with a

small amount of wetting agent added, gave good experimental

results. A 5-percent solution ofsoluble starch as a dip gave good

results at the time of treatment, but date surfaces with bloom

retained too much material. The coating from these surfaces

later peeled and left a dull surface. Schiller and Maier {100)

recommended 6 percent soluble starch or 3 percent methyl

cellulose for coating dates.

BLEMISHES

The appearance and texture of dates are sometimes seriously

impaired by blemishes caused by unfavorable environmental

conditions during the growing season or by mites. No pathological organism has been found associated with these defects. The

incidence varies among types and cultivars and from season to

season within a given cultivar. The more important blemishes

found on American dates are blacknose, black scald, and puffiness or skin separation.

Blacknose

Severe checking of the skin of some date cultivars, induced by

high humidity just before the beginning of the khalal stage,

results in darkening, shriveling, and hardening of the flesh at

the tip of the fruit. This condition, known as blacknose, and in

some cases as sugartip, lowers the grade of the fruit, and ii

severe, may cause it to be culled {68), The Deglet Noor is

especially prone to develop this blemish.

Black Scald

Black scald consists of a blackened and sunken area with a

definite line of demarcation. It appears at tlie tip or on the side?

of the fruit. The appearance suggests exposure to high temperatures, but the cause is not definitely known {68).

Puffiness or Skin Separation

Puffiness usually affects only soft cultivars of dates, and these

differ in susceptibility. The condition develops during ripening

and may or may not increase during curing and drying. Puffi-
DATE DEVELOPMENT IN THE UNITED STATES 37

ness causes dates to lose grade, and is especially objectionable if

the separated skin becomes hard and brittle.

The cause of puffiness is not known, but high temperature or

high humidity, or both, at a stage before the beginning of

ripening, may predispose the dates to skin separation. Reducing

the number of strands in a bunch tends to reduce the affliction;

whereas, severe cutting back of the strands tends to aggravate

it (¿V, 68).

Gefen and Fahn (S2) found that the skin of Barhi dates, which

blistered badly, had fewer stomatal cells than the Dairi, which

formed no blisters; the skin of the Barhi also was less elastic.

Dates dried at 113''F (45° C) formed fewer blisters than those

dried at 149° F (65° C). Dates dipped in a wax substance, especially Myvocet, formed fewer blisters than undipped dates, and

the treatment did not affect drying.

RESPIRATION

Since the rate of respiration by ripe dates is so low, it does not

need to be considered in selecting the materials to be used for

packaging the fruit. The rate increases as the moisture content

increases. Cured Deglet Noor dates, with 20 to 22 percent

moisture, produce about 0.4 milligram (mg) carbon dioxide per

kilogram per hour at 75° F (24° C). The rate is about 2 mg in

dates with 27 percent moisture.'* These rates compare with about

27 mg in oranges and 61 mg in peaches, both at 70° F (21° C) (37).

The presence of growing mold, yeast, and bacteria on the dates

materially increases the apparent rate of respiration and the

need for aeration.

According to Hussein and Aref U5), respiration in dates

reaches a climacteric peak when the color begins to change from

green to yellow or red. Luthra and Chima (50) observed a similar

rise to a maximum in Malta oranges at the onset of the change

from green to yellow.

Both enzymatic and nonenzymatic reactions cause oxygen to

be absorbed and carbon dioxide to be produced. Nonenzymatic

reactions cause about two-thirds of the gas exchange in date

flesh. Enzymatic reactions are involved in enzymatic browning

as well as in normal respiration. Only a small fraction of the

total oxygen absorbed and carbon dioxide produced is associated

with true respiration. Seed respiration accounts for about onefifth of the gas exchange in whole dates (59),

-* BARGER, W. R. COLD STORAGE OF DATES. Office report, 52 pp. 1937.
38 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

PLANT SANITATION

Certain practices are necessary to promote a high degree of

sanitation in any plant in which food is handled. The need for

such practices in a date packing plant is apparent because of the

high sugar content of the product and the resulting tendency of

objects coming in contact with the dates to become sticky. These

sugary films provide places for the growth of innumerable

populations of micro-organisms.

Practical measures for controlling mierobial growth have been

suggested by Vaughn, Winter, and Smith (ii^) and by Sharpies

{101}, Equipment and workers' hands coming in contact with the

fruit should be cleaned and sanitized continuously or at frequent

intervals. They suggest hand cloths should be rinsed in a

sanitizing solution at frequent intervals, and the rinse water

should be changed at least every 2 hours. They recommend

conveyar belts should be cleaned and sanitized continuously by

using a revolving brush or, preferably, by using an immersion

type of belt sanitizer. A squeegee is used to dry the belt.

Disadvantages of these methods are that workers have to

remember to use the hand cloths, and the treated water used to

sanitize the hand cloths and the belts must be changed at

intervals not exceeding 2 hours to avoid bacterial buildup. A

continuously chlorinated spray, rather than an immersion belt

cleaner, would avoid part of this problem.

A continuous cleaning arrangement has the advantage of

obviating the need to stop the belt periodically for cleaning, or

running it without a load long enough to allow hand cleaning.

Furthermore, as it is always clean, no extensive cleanup is

required at the end of the day. Reagents found to be effective in

reducing mierobial population {112) were hypochlorite and chloramine-T. Sharpies (iOi) obtained slightly better bacterial control

with a quaternary ammonium compound than with hypochlorite.

FORMS OF DETERIORATION

Two general forms of deterioration affect dates, pathological

and nonpathological.

Pathological

The micro-organisms concerned in pathological date spoilage

fall into the three general groups: Yeasts, molds, and bacteria.

Of these, yeasts are of greatest economic importance. The most

harmful yeasts are those capable of growing in relatively con-
DATE DEVELOPMENT IN THE UNITED STATES 39

centrated solutions of sugar. Species of Zygosaccharorayces are

more tolerant of high sugar concentrations than others found in

dates, and these are followed by a species of Hansenula {68, 6Jf,

65), Dates that have been attacked by yeast can be detected by

an alcoholic odor. White aggregates, which include yeast cells,

may often be seen in skin cracks of badly fermented dates. Gas

pockets may form under the skin, the flesh may be discolored,

and the flavor is noticeably impaired. When the moisture content is just high enough to allow slow yeast growth, the dates

gradually develop undesirable odor and flavor.

Molds are of little consequence in the spoilage of commercially

packed dates except in very moist lots. They may cause large

losses before and just after the fruit is harvested if rains or

periods of high humidity occur at that time. Species of Aspergillusy Alternaría, and Pénicillium are the most common molds

found in dates. Mold growth may be detected by mycelia and

spores and by color, odor, and flavor. These organisms usually

develop before the dates are cured or dried because they cannot

develop on the cured product. Catenularia fuliginea Saito is

capable of growing on dates that are somewhat drier than the

fungi previously mentioned and appears occasionally on packaged dates in the market. Even this mold organism requires a

fairly moist date to develop (25, 65, 110).

The role of bacteria in date spoilage has not been determined

with any degree of certainty. Ac^ioftact^r is known to convert the

alcohol produced by yeast into acetic acid; the odor of vinegar is

sometimes pronounced in spoiled dates. In this event, the dates

are already ruined commercially before the bacteria become

active. Lactic acid bacteria have been suggested as possible

contributors to the gradual deterioration of dates {86, 68,101),

Whatever deterioration may be caused by bacteria, its economic importance compared with the deterioration caused by

yeasts and molds is in all probability exceedingly small. The

bacterial population on dates at harvest is of the same order of

magnitude as that of molds {101).

Nonpathological

Aside from the obvious and very objectional molding and

fermentation caused by pathological factors, dates may darken,

become sirupy, develop sugar spots, lose flavor, become too dry

or too moist, or develop an objectionable granular texture.

Hydrolytic changes, including the inversion of sucrose into reducing sugars (fructose and glucose, or invert sugar), occur more

rapidly at high than at low temperatures and at high than at
40 AGRICULTURE HANDBOOK 482, U.S. DEFT. OF AGRICULTURE

low moisture contents. The same is true of acid production. Most

of this acid is produced by nonoxidative, nonenzymatic reactions

(58, 59, 60). The acidity increases even if the dates have been

heated as in hydration or fumigated with a volatile fungicide

such as ethylene oxide {99), Fermented dates have considerably

more acid than sound ones as a result of the bacterial conversion

of some of the alcohol to acetic acid.

The rate of darkening varies with ternperature and moisture

content, and possibly with cultivar and previous treatment.

Darkening is the result of both oxidative and nonoxidative

reactions (58, 5U, 55, 57), Oxidative darkening can be reduced by

storage in inert gas or vacuum {59, 60, 79), General darkening

can be delayed by lowering the storage temperature and reducing the moisture content {98, 9J^),

A form of deterioration, perhaps less serious than those already described, is that of sugar spotting. Sugar spotting reduces the market value by disfiguring the affected dates rather

than by making them inedible. The light-colored spots under the

skin are composed mainly of sugar crystals and may be removed

by gentle heating. They will reappear on standing, however, if

conditions are suitable for their formation. Fine sugar crystals

sometimes form on the surface of dates and have been referred

to as "sugar bloom." These, too, are readily removed by gentle

heating.

Sugar spotting is restricted almost entirely to the invert sugar

type of dates and appears only rarely in cane sugar types such

as Deglet Noor. Sugar crystals may form^ however, within the

flesh of Deglet Noor dates as they become old. Deglet Noor dates

that have sugar spots do not have abnormally high reducing

sugar content. Analysis of such dates showed that only 25

percent of the sugar was in the reducing form.

Practically all soft cultivars grown in the United States are of

the invert sugar type, but the cultivars within this group vary

considerably in their tendency to form sugar spots. Several of

the semidry cultivars and nearly all of the dry cultivars contain

large amounts of sucrose (16, 17) and are much less subject to

sugar spotting.

Temperature and moisture content influence the development

of sugar spots in a given cultivar. Lowering the temperature

below ordinary room temperature reduces the rate of formation.

Soft cultivars of dates are most prone to spot when the moisture

percentage is in the high 20's. Little or no spotting is likely to

occur in dates with a moisture content higher than about 33

percent, and spotting decreases as the moisture falls below 22

percent (6, U8, 81, 101),
DATE DEVELOPMENT IN THE UNITED STATES 41

PACKAGING

The percentage of the American date crop that is placed in

consumer packages before it is shipped from the area of production has increased over a period of years. In 1970, about 85

percent was handled in this manner.

Most of the nonprepackaged Deglet Noor dates are marketed

in 15-pound flats of fiberboard or wood. Others are packed in 5-

and 10-pound cartons. Soft cultivars must be packed in shallow

containers to avoid crushing unless they are thoroughly cured.

Large reinforced fiberboard cartons are used for packing dry

grades for export. Such dates are not readily damaged by

crushing. Figure 13 shows such cartons being check weighed and

readied for lidding and loading.

A variety of sizes of packages increases date sales over the

display of only one size {33, 75, 106). Consequently, consumer

FN-4393

FIGURE 13.—A dry-type Deglet Noor date is packed in large fiberboard

cartons for export and subsequent processing. Each package is checked

for full weight.
42 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

packages are made in a number of sizes and shapes. They range

in size from 8 ounces or less to 3 pounds. In addition, small

quantities are packed in 2-ounce bags for eating out of hand. The

containers may be bags of transparent film or trays overwrapped with film. Round fiberboard cans with metal tops and

bottoms are used for some of the better grades; these contain 1

to 3 pounds. All-metal cans with friction tops are used, and rigid,

transparent, 8- and 12-ounce plastic containers have received

excellent consumer acceptance. These plastic containers are

shown check weighed in figure 14.

To prevent mold and fermentation in the packages, small,

carefully measured portions of a volatile fungicide were introduced into the containersjust before they were closed. Formerly,

the active ingredient most commonly used for this purpose was

FIGURE 14.—Pitted dates are packed in 8-ounce plastic containers. Each

container is weighed to assure full weight.
DATE DEVELOPMENT IN THE UNITED STATES 43

ethylene oxide, but propylene oxide also wa& used. The amount

added varied with the nature of the container and the composition of the mixture (65, 116). These materials are not currently

allowed in the United States.

A small quantity of dates has been canned with varying

degrees of success. Good results have been achieved by the use

of a method in which the dates are held under vacuum (67), The

sealed cans are immersed in water at about 190° F (88"* C) for 30

to 45 minutes to destroy micro-organisms. The specific conditions

are governed by the nature of the dates. Since canned dates may

be kept on store shelves or in warehouses longer than the dates

are likely to remain in good, tasty, and attractive condition,

special precautions should be taken by the packers and distributors to make certain that no cans remain in the market channels

from one season to the next. Consumer acceptance of this

package has not been good, probably because of the lack of

visibility, the increased cost, and the presence of old packs on the

shelves.

STORAGE

American dates were kept in cold storage at least as early as

1916. F. W. Butler and Sons of San Francisco stored fresh dates

successfully at 34° to 36° F (1° to 2° C) for 5 months from

September 1916 to February 17, 1917. In 1917, they stored

Hayany dates up to 6 months. The dates that were partly dried

before storage retained the best flavor {26), Later experience has

shown that some of the water should be removed from very

moist dates before they are stored. Present information on the

Hayany suggests that the dates stored by Butler without drying

probably contained about 50 percent water.

Dates are usually placed in cold storage after they have been

cleaned, graded, and, if necessary, matured and dehydrated.

Dates to be sold in bulk are often packed in 15-pound containers

before they are stored. At the peak of harvest, when packinghouses receive dates more rapidly than they can handle them, a

considerable tonnage may be placed in cold storage until packing

facilities become available. This practice results in a better

product than if the surplus dates are allowed to remain at

prevailing room temperatures over an extended period. To get

the full benefit of cold storage, the dates should be cooled as

rapidly as possible after they are placed in storage. Quick cooling

is promoted by proper stowing of the containers, good air

circulation, and air temperature low enough to produce the

desired conditions (5).
44 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

The most desirable temperature for date storage is determined

by considering the cost in relation to the minimum requirements

of the dates. The keeping quality of all dates apparently improves as the temperature is lowered within reasonable limits.

The lower limit of storage temperature is governed by the cost

and not by the effect of low temperatures on the dates. In any

discussion of storage temperatures for dates, the recommended

temperatures are the highest at which dates of a given description are likely to retain acceptable quality for the required

length of time. Lower temperatures conserve the quality better

than the temperatures recommended but they cost more.

Deglet Noor and similar varieties retain good quality up to 1

year at 32° F (0° C), Soft types should be stored at 0° F (-18° C) to

retain good color and flavor and to minimize sugar spotting.

Both temperature and moisture content are important in

limiting the storage life of dates {9S, 9Í), Figure 15 shows the

general effect these factors have on the storage life of Deglet

Noor dates.

Storage at temperatures of 32° F (0° C) or lower for a month

very substantially reduces the population of yeasts, molds, and

bacteria. A complete kill is not accomplished, however, and upon

return to favorable temperatures the surviving organisms resume activity and under suitable conditions can cause spoilage

(101), Modern facilities permit stacking palletized cartons of

packed dates to the ceiling of high cold storage rooms.

The humidity of the storage room is important unless the

dates are enclosed in moisture-proof containers or the tempera35

0:30

hi 25

Ö20

\\

1 1 V \ 1

-

\ ^^^-...___32°F "

\ ^^^^^^.^.....^jJO^F

— \^0^F

1 1^ Y^\ 1

6

MONTHS

10 12

FlGlFRE 15.—^Effects of temperature aird moisture content on storage life of

Deglet Noor dates.
DATE DEVELOPMENT IN THE UNITED STATES 45

ture is somewhat lower than 32° F (0° C). The relative humidity

required to maintain constant moisture in the dates depends on

the initial moisture content and on the temperature of the

storage space (22, 86, 88), Constant temperature is important to

avoid undue fluctuations in the relative humidity and the consequent drying or moistening of portions of the stored dates. Soft

types require slightly lower storage humidity to maintain a

constant moisture content than Deglet Noor with the same

moisture content.

At the point of production, cleaned and graded dates are

stored only in bulk containers such as 15-pound flats and 30-

pound lugs and more recently in bulk bins holding 750 to 1,000

pounds. Consumer-sized packages are filled just prior to shipment to distributors. By this practice, fresh appearing packages

are sent to the distributors, and dates that may have become

unfit for packaging while in storage may be eliminated.

Dates stored with other aromatic products are likely to absorb

the flavors of their neighbors. It is therefore essential that the

air in the storage rooms be free from foreign aromas. The flavors

of apples, onions, and potatoes were noted in dates stored with

these products at ordinary cold storage temperatures, and the

flavor of meat was very marked in dates stored in frozen food

locker plants in the same room with meat (109),

TRANSPORTATION

A low transit temperature is desirable for dates, but the dates

should be cooled before they are loaded into the railroad car or

truck. Removing the heat from the loaded packages is a slow,

difficult, and expensive process. This is so because most dates

are packed in tight consumer packages which are in turn packed

in tight master containers. The master containers are stowed

tightly in the vehicle with no provision for refrigerated air to

pass through or between the containers.

Date temperatures during transit in iced refrigerator cars were

measured with recording thermometers in 12 test shipments

made to New York. The services varied from no ice to fullbunker standard refrigeration (daily re-icing). Loading temperatures were 52° to 100° F (IV to 37° C). Some cars were equipped

with circulating fans and wall flues; others had neither. The

dates were packed in wooden flats or in fiberboard cartons. The

flats contained 15 pounds of bulk dates, and the cartons contained twenty-four 8-ounce film-over-wrapped packages.

Representative temperatures at the middle layer, quarter-
46 AGRICULTURE HANDBOOK 482, U.S. I>EPT. OF AGRICULTURE

length, center-line position are shown in figure 16 from Rygg

(95). In fan-equipped cars, the temperature at this position is

generally lowered somewhat less rapidly than in top or bottom

layers where surface exposure to air is greater. In nonfan cars,

middle-layer temperature reduction is usually intermediate between the slow cooling in top layers and rapid cooling in bottom

layers, but because of the tight load in date cars, even the top

layers cool more rapidly than tlie middle layers.

The amount of cooling en route was from none (not shown in

fig. 16) to a loss of 29*^ F (16^ C) (car A, fíg;16). The cooling in eight

of the loads was 10** F (6** C) or less.

The poor cooling can be attributed to lack of circulation of air

through the load. The amount ofice and the presence or absence

offans had little or no effect. The greatest amount of cooling was

obtained in car A under standard refrigeration with full bunkers. This car was not equipped with fans. The load, which

100

^F 80 -

4 6

DAYS

FlGVBE 16.—^Transit temperatures of dates under various iciug services.
DATE DEVELOPMENT IN THE UNITED STATES 47

consisted of dates packed in 15-pound wooden flats, permitted a

fair amount of vertical air movement. The load in another car

(not shown in fig. 16) refrigerated in the same manner but

loaded with dates in cartons cooled by only 4° F (2° C). Although

this car was equipped with air-circulating fans, almost no heat was

removed from the load. Practically no air circulation could take

place within the loads of cars containing dates in cartons. The

dates were enclosed in sealed film packages, and these were

enclosed in nonventilated fíberboard cartons. The cartons were

lock loaded with the layers alternating, thus effectively preventing

vertical air movement. Tight stowing also prevented lateral air

movement.

In view of the small amount of cooling in transit, especially in

loads of dates in cartons, the refrigeration service is probably

not worth the cost. A more effective and less costly method of

maintaining date quality is to cool the dates before they are

loaded into the car. Since dates produce very little heat from

respiration, only enough refrigeration is then required to remove heat entering from the outside.

Dates,^ like other dried processed fruits, should be stored and

shipped at cool temperatures, with a generally recommended

upper maximum of 45"* F (7'' C). During hot weather, properly

precooled dates should be shipped in refrigerated railcars, truck

vans, or ship containers set at 35° to 40° F (2° to 4° C) to avoid the

warming and later deterioration that may occur in outer packages

of dates in nonrefrigerated shipments. If dates are not precooled,

refrigeration costs are largely wasted unless the dates are packaged in vented cartons and stacked in a pattern allowing cooling of

the product. During cooler parts of the year, refrigeration is not

necessary. Low-temperature protection is not needed as freezing

does not harm dates.

Dates should be marketed soon after removal from cold storage;

otherwise the benefits of cold storage are gradually lost. Dates

stored 1 year at 32° or 0° F (0° or -18° C) were acceptable after 1

month at 70° F (21° C), but after 2 months they had darkened and

lost flavor noticeably, and after 3 months benefits of the previous

cold storage were lost (95), Dates stored at warmer temperatures

deteriorated faster when held at 70° or 80° F (21° or 27° C) during

shipping or marketing {9S),

Moisture content of dates, temperature during storage, and time

5 The rest of this section on 'Transportation" was prepared by L. G. Houck,

plant pathologist, USDA, ARS, Riverside, Calif., to reflect changes in the

industry since original preparation of the manuscript.
48 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

of holding all affect date quality. Drier dates (18 to 26 percent

moisture) are expected to have somewhat longer storage life,

especially at the higher temperatures; more moist dates (26 percent moisture or more) have shorter storage life {9U)- Transit and

marketing life is dependent upon condition of the dates at the time

they are shipped as well as their shipping and distribution temperatures. Much of the date crop is distributed from the packinghouses in trucks, as shown in figure 17.

FIGURE 17.—Palletized date packages being loaded into trucks. PN-4395

LITERATURE CITED

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1935. DATE GROWING IN ARIZONA. Ariz. Agr. Expt. Sta. BuL

149: 231-286.

(2) ALI, K. T., FINE, N. C, SARSAM, N. H., and MCLEROY, G. B.

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(3) AsHMAWi, H., AREF, H., and HUSSEIN, A. A.

1956. COMPOSITIONAL CHANGES IN ZAGLOUL DATES THROUGHOUT THE

DIFFERENT STAGES OF MATURITY. Jour. Sei. Food Agr. 7: 625-

628; Chem. Abs. 51: 632 i.
DATE DEVELOPMENT IN THE UNITED STATES 49

(4) AsHMAWi, H., HUSSEIN, A. A., and AREF, H.

1955. CHEMICAL CHANGES IN SAMANI DATES DURING GROWTH AND

RIPENING. Cairo Univ., Faculty Sei. Bul. (Giza, Egypt) 60: 3-13.

(5) BARGER, W. R.

1933. EXPERIMENTS WITH CALIFORNIA DATES IN STORAGE. DATE

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(6)

(7)

1934. THE EFFECT OF HUMIDITY AND CONTAINERS ON DATES. Date

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1936. EXPERIMENTS IN HYDRATING DRY DEGLET NOOR DATES. Date

Growers' Inst. Rpt. 13: 14-16.

(8) and SlEVERS, A. F.

1927. EXPERIMENTS IN STORAGE OF DEGLET NOOR DATES. Date

Growers' Inst. Rpt. 4: 9-10.

(9) BooHER, L. E., HARTZLER, E. R., and HEWSTON, E. M.

1942. A COMPILATION OF THE VITAMIN VALUES OF FOODS IN RELATION

TO PROCESSING AND OTHER VARIANTS. U.S. Dept. Agr. Cir.

638, 244 pp.

(10) BROWN, T. W., and BAHGAT, M.

1938. DATE PALM IN EGYPT. Govt. Press, Bulaq, Cairo.

(11) CHATFIELD, CHARLOTTE, and ADAMS, GEORGIAN.

1940. PROXIMATE COMPOSITION OF AMERICAN FOOD MATERIALS. U.S. Dept. Agr. Cir. 545, 91 pp.

(12) CLAGUE, J. A., and FELLERS, C. R,

1933. TIME, TEMPERATURE AND HUMIDITY RELATIONSHIPS IN THE

PASTEURIZATION OF DATES. Arch. f. Mikrobiol. Bd. 4, S 419-

426.

(13) CLEVELAND, M. M., and FELLERS, C. R.

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(14) COGGINS, C. W,, JR., and KNAPP, J. C, F.

1969. GROWTH, DEVELOPMENT, AND SOFTENING OF THE DEGLET NOOR

DATE FRUIT. Date Growers' Inst. Rpt. 46: 11-14

(15) KNAPP, J. C. F., and RICKER, AUCE L.

1968. POST-HARVEST SOFTENING STUDIES OF DEGLET NOOR DATES:

PHYSICAL, CHEMICAL, AND HISTOLOGICAL CHANGES. Date

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(16) COOK, J. A., and FuRR, J. R.

1952. SUGARS IN THE FRUIT OF SOFT, SEMI-DRY, AND DRY COMMERCIAL

DATE VARIETIES. Date Growers' Inst. Rpt. 29: 3-4.

(17) and FuRR, J. R.

1953. KINDS AND RELATIVE AMOUNTS OF SUGAR AND THEIR RELATION

TO TEXTURE IN SOME AMERICAN-GROWN DATE VARIETIES. Amer. Soc, Hort. Sei. Proc. 61: 286-292.

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1940. DRYING DATES UNDER ADVERSE WEATHER CONDITIONS. Date

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1959. TEMPERATURE AND ITS RELATIONSHIP TO THE DATE CROP. Date

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50 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

(20) COOK, W, W.

1939, WHEN TO HARVEST—PISCUSSION. Date Growers' Inst. Rpt.

16: 3-6,

(21) CRUESS, W. V.

1940, DATES AND DATE PRODUCTS IN EGYPT AND CALIFORNIA. Date

Growers' Inst, Rpt. 17: 20-27.

(22) POWSON, V. H. W., and ATEN, A.

1962, DATES» HANDLING, PROCESSING AND PACKING. FAO Agr.

\ Devlpmt. Paper 72, 392 pp. Rome.

(23) ELMER, H, S,

1968, EVALUATION OF THE EFFECTS OF MALATHION DUST APPLICATIONS FOR THE CONTROL OF DATE-INFESTING INSECTS. Date

Growers* Inst, Rpt, 45: 12-13.

(84) FATTAH, M. T.

1927, CHEMICAL STUDIES OF DATES. Date Growers' Inst. Rpt. 4: 10-

12.

(26) FAWCETT, H. S., and KLOTZ, L. J.

1932. DISEASES OF THE DATE PALM, **PHOENIX DACTYLIFERA." Calif.

Agr, Expt, Sta. Bui, 522, 47 pp.

(26) FORBE$. R. H.

1917, THE DATE ORCHARD, Ariz, Agr. Expt. Sta. Ann. Rpt, 28: 442-

451,

(27) FREEMAN, G. F.

19U, RIPENING DATES BY INCUBATION. Ariz. Agr. Expt. Sta. Bui.

66: 437^56.

tm FURR. J, R., and ARMSTRONG, W. W., JR.

1959, THE RELATION OF GROWTH, YIELD AND FRUIT QUAUTY OF DEGLET NOOR DATES TO VARIATONS IN WATER AND NITROGEN

SUPPLY AND TO SALT ACCUMULATION IN THE SOIL. Date Growers* Inst, Rpt. 36: 16-18.

(29) .....,— and ARMSTRONG, W, W., JR,

1960, INFLUENCE OF SUMMER OR FALL DROUGHT ON HARD END AND

IMMATURE SHATTER OF HALAWY DATES. Date Growers' Inst.

Rpt, 37: 7-9.

(30) ^ and ARMSTRONG, W, W., JR.

1962. A TEfifT OF MATURE HALAWY AND MEDJOOL DATE PALMS FOR

SALT TOLERANCE. Date Growers' Inst. Rpt. 39: 11-13.

(31) , ^ ARMSTRONG, W. W„ JR., and LiEU, P. S.

1961, FRUIT QUAUTY IN RELATION TO CROP LOAD OF DEGLET NOOR

DATES. Date Growers' Inst. Rpt, 38: 4-5.

(32) GEFBN, M., and FAHN, A.

1967, **LISTER" FORMATION IN DATES. Israel Jour. Bot. 16: 53-54

(abstract only). Hort. Abs. 38(3): Sept. 1968, No. 6501,

(33) GOLDSBOROUGH, G. H.

1958. VARIETY IN PACKAGE SIZE INCREASES DATE SALES. U.S. Dept.

Agr, Agr. Market Serv, AMS Mimeo.

(34) HAAS, A. R. C.

1035, INORGANIC COMPOSITION OF DATE FRUITS. Date Growers' Inst.

Rpt. 12: 6-8.

(35) '^ and Buss, D. E,

1935, GROWTH AND COMPOSITION OF DEGLET NOOR DATES IN RELATION TO WATER INJURY. Hilgardia 9: 295-544.
DATE DEVELOPMENT IN THE UNITED STATES 51

(36) HAPAYAH, H. W.

1954. BACTERIOLOGICAL STUDIES ON DATES. Date Growers' Inst.

Rpt. 31: 5-6.

(37) HALLER, M. H., HARDING, P. L., LUTZ, J. M., and ROSE, D. H.

1931. THE RESPIRATION OF SOME FRUITS IN RELATION TO TEMPERATURE. Amer. Soc. Hort. Sei. Proc. 28: 583-589.

(38) HASEGAWA, S., MAIER, V. P., KASZUCKI, H. P., and CRAWFORD, J. K

1969. POLYGALACTURONASE CONTENT OF DATES AND ITS RELATION

TO MATURITY AND SOFTNESS. Jour. Food Sei. 34: 527-529.

(39) and SMOLENSKY, D. C.

1970. DATE INVERTASE: PROPERTIES AND ACTIVITY ASSOCUTED WITH

MATURATION AND QUAUTY. Agr. and Food Chem. 18(5): 902-

904.

(40) HEFTMANN, E., KO, S. T., and BENNETT, R. D.

1965. IDENTIFICATIONS OF ESTRONE IN DATE SEEDS BY THIN LAYER

CHROMATOGRAPHY. Naturwissenschaften 52: 431-432.

(41) HILGEMAN, R. H., SHARPLES, G. C, and HOWLAND, L. H.

1957. EFFECT OF IRRIGATION AND LEAF-BUNCH RATIO ON SHRIVEL

AND RAIN DAMAGE OF THE MAKTOOM DATE. Date Growers'

Inst. Rpt. 34: 2-5.

(42) and SMITH, J. G.

1937. THE CRUDE FAT CONTENT OF DATE SKINS CORRELATED WITH

MOISTURE DAMAGE. Date Growers' Inst. Rpt. 14: 16-17.

(43) and SMITH, J. G.

1938. MATURATION AND STORAGE STUDIES WITH SOFT VARIETIES OF

DATES. Date Growers' Inst. Rpt. 15: 14-17.

(44) HODGSON, ROBERT W.

1^37. DATE CULTURE IN THE PUNJAB, INDIA. Date Growers' Inst.

Rpt. 14: 3-4.

(45) HUSSEIN, A. A., and AREF, H,

1955. THE RESPIRATION OF FRESH DATES THROUGHOUT MATURITY. Cairo Univ., Faeulty Sei. Bul. 59, 10 pp.; Chem. Abs.

51: 16742 f. (1957).

(46) HYDE, JAY.

1948. PROCESSING ARIZONA DATES. Ariz. Date Inst., 20 pp.

(47) LiNDGREN, D. L., and VINCENT, L. E,

1953. EXPERIMENTS ON THE CONTROL OF INSECTS INFESTING DATES IN

BUNCHES. Date Growers' Inst. Rpt. 30: 14-16.

(48) LLOYD, F. E.

1910. DEVELOPMENT AND NUTRITION OF THE EMBRYO, SEED AND

CARPEL IN THE DATE, "PHOENIX DACTYLIFERA" L. Mo. Bot.

Gard. Ann. Rpt. 21: 103-164.

(49) LONG, E. M.

1943. DEVELOPMENTAL ANATOMY OF THE FRUIT OF THE DEGLET NOOR

DATE. Bot. Gaz. 104: 424-436.

(50) LUTHRA, J. C, and CHIMA, I. S.

1940. SOME STUDIES ON THE METABOLISM AND GROWTH OF MALTA

ORANGES. Indian Aead. Sei. Proc. IIB: 61-70.

(51) MAIER, V, P.

1963. HY0ROXYCINNAMOYL ESTERS OF QUINIC AND SHIKIMIC

ACIDS. In Aspects of Plant Phenolic Chemistry (ch. 4). Third

Ann. Symposium of the Plant Phenolics Group of North America Proc.
52 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

(52) MAIER, V. P., and METZLEJI, D. M.

1961. SUCROSE INVERSION IN DEGLET NOOR DATES AND ITS PROCESSING APPUPATIONS. Date Growers' Inst. Rpt. 38: 6-9.

(53) and METZLER, D. M.

1964. PHENOLIC CONSTITUENTS OF THE DATE ("PHOENIX DACTYUFERA'O AND THEIR RELATION TO BROWNING. First Internat.

Cong, of Food Sei. ^nd Technol. Proc, London, Sept. 18-21,1962,

pp. 445-453.

(54) and METZLER, D. M.

1965. QUANTITATIVE CIÎANGBS IN DATE POLYPHENOLS AND THEIR RELATION TO CROWNING. Jour. Food Sei. 29(5): 565-668.

(55) and METZLER, D. M.

1965. QUANTITATIVE CHANGES IN DATE POLYPHENOLS AND THEIR RELATION TP BROWNING. Jour. Food Sei. 30(1): 80-84.

(56) METZLER, D. M., and HUBER, A. F.

1964. EFFECTS OF HEAT PROCESSING ON THE PROPERTIES OP

DATES. Date Growers' Inst. Rpt. 41: 8-9.

(57) METZLER, D, M., and HUBER, A. F.

1964. 3-0-CAFFEOYLSHIKIMIC ACID (DACTYLIFRIC ACID) AND ITS ISOMERS, A NEW CLASS OF ENZYMIC BROWNING SUBSTRATES. Bioehem. and Biophys. Res. Commun. 14(2): 124-

128.

(58) and ScHILLER, F. H.

1959. PROGRESS OF CHEMICAL STUDIES OF DEGLET NOOR

PATES. Date Grower?' Inst. Rpt. 36: 8-10.

(59) and SCHILLER, FR^NK H.

1961. STUDIES ON DOMESTIC DATES. IJ, SOME CHEMICAL CHANGES

ASSOCIATED WITH DETERIORATION. Jour, of Food Sei.

26(3): 322-328.

(60) and SCHILLER, FRANK H.

1961. STUDIES ON DOMESTIC DATES. IE. EFFECT OF TEMPERATURE ON

SOME CHiîMICAL CHANGES ASSOCIATED WITH DETERIORATION. Jour, of Food Sei. 26(5): 529-534.

(61) MoNciERo, ARMAND.

1954. NOTES SUR LE PALMIER-DATTIER. Ann. de I'Inst. Agr. Serv. de

Reeh. et d^Ejçpt. Agr. de I'Algeria 8: 4.

(62) MORRIS, J. S., and GODFREY, G. H.

1948. A NEW METHOD POi^ RIPENING DATES. Tex. Agr. Expt. Sta.

Prog. Rpt. U89, 3 pp.

(63) MRAK, E. M.

1941. THE DETERIORATION OF DATES. Date Growers' Inst. Rpt.

18: 3-4.

(64) PHAFF, H. J.. and VAUGHN, R. H.

1942. YEASTS OCCURRING ON PATES. Jour. Bact. 43: 689-700.

(65) and STADTMAN, THRESSA.

1946. MICROBIOLOGICAL DETERIORATION OF DRIED FRUITS. Date

Growers* Inst. Rpt. 2$; 19-23.

(66) NADA, I. A. A., and HASSAN, H. M.

1956. EFFECT OF SODIUM CHLORIDE ON SOFTENING AND CARBOHYDRATE CHANGES OF DATE FRUITS. Nature (London) 175: 735-

736.
DATE DEVELOPMENT IN THE UNITED STATES 53

(67) NIELSEN, B, W., MCCüLLOCIí, R. J., and BEAVENS, E. A.

1950. PROCESSING AND PACKAGING DATES. L A NEW METHOD OF

CANNING AND PASTEURIZING DEGLET NOOR DATES. Food Technol. 4: 232-237.

(68) NixON, R. W.

1951. DATE CULTURE IN THE UNITED STATES. U.S. Dept. Agr. Cir.

728, 57 pp., rev.

(69)

(70)

(71)

V (72)

1951. THE DATE PALM—^TREE OF LIFE" IN THE SUB-TROPICAL DESERTS. Econ. Bot. 5: 274-301.

1959. EFFECTS OF GIBBERÈLLÎN ON FRUITSTALKS AND FRUIT OF DATE

PALM. Date Growers' Inst. Rpt. 36: 5-7.

1961. SKIN SEPARATION IN SOFT DATES. Date Growers* Inst. Rpt.

38: 10-13.

1963. QUAUTY OF bEGLET NOOR DATES IN RELATION TO METHOD OF

HARVESTING. Date Growers' Inst. Rpt. 40: 10.

(73) and FuRR, J. R.

1961, QUAUTY OF DEGLET NOOR DATES IN RELATION TO FREQUENCY

OP PICKING. Date Growers* Inst. Rpt. 38: 14-15.

(74) and FuRR, J. R.

1962. FREQUENCY OF PICKING IN RELATION TO QUAUTY OF DEGLET

NOOR DATES IN 1961. Date Growers' Inst. Rpt. 39: 16-18.

(75) PEIGHTAL, B. J.

1958. VARIETY IN PACKAGE SIZE INCREASES DATE SALES. Date Growers' Inst. Rpt. 35: 9-12.

y (76)

1962. REMARKS ON THE MECHANIZATION OF Í)ATE HARVESTING. Date

Growers' Inst. Rpt. 39: 18.

(77) PERKINS, R. M., and BROWN, G. KL

1964. PROGRESS IN MECHANIZATION OF DATE HARVESTING. Date

Growers' Inst. Rpt. 41: 19-23.

(78) PITTSBURGH UNIVERSITY.

1949. NUTRITIONAL DATA (FORMERLY "NUTRITIONAL CHARTS"). 114

pp., illus. (Compiled by Wooster, H. A., Jr., and Blanck, F. C.)

Mellon Institute of Industrial Research, Pittsburgh, Pa.

(79) RASHID, I. M.

1950, OXIDIZING ENZYMES IN DATES IN RELATION TO THE DARKENING

OF THE FRUIT. Ph.D. thesis, Mass. Univ.

(80) RINDERKNECHT, H.

1959. THE FREE AMINO ACID PATTERN OF DATES IN RELATION TO

THEIR DARKENING DURING MATURATION AND STORAGE. Food

Res. 24(3): 298-304.

(81) RYGG, G. L.

1942. FACTORS AFFECTING SUGAR SPOTTING IN DATES. Date Growers' Inst. Rpt. 19: 10-12.

(82)

1944. GLAZING AND HYDRATING DATES. Date Growers' Inst. Rpt.

21: 7-10.
1946. COMPOSITIONAL CHANGES IN THE DATE FRUIT DURING GROWTH

AND RIPENING. U.S. Dept. Agr. Tech. Bui. 910, 51 pp.

1946. UTILIZATION OF UNPOLUNATED DEGLET NOOR DATES. Date

Growers' Inst. Rpt. 23: 36-38.

1948. RELATIVE HUMIDITY FOR STORING DATES. Amer. Soc. Hort. Sei.

Proc. 52: 173-175.

1948. ACIDITY IN RELATION TO QUAUTY IN THE DATE FRUIT. Date

Growers' Inst. Rpt. 26: 32-33.

1948. STORAGE HUMIDITY FOR DATES. Date Growers' Inst. Rpt.

25: 34-35.

19Ö0. INVESTIGATIONS ON HARVESTING DEGLET NOOR DATES INCLUDING BUNCH CUTTING AND DELAYED PICKING. Date Growers'

Inst. Rpt. 27: 22-25.

54 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

(83) RYGG, G. L.

1945. DETERMINATION OF MOISTURE IN DATES BY MEANS OF A REFRACTOMETER. Date Growers' Ins^. Rpt. 22: 3-4.

(84)

(85)

(86)

(87)

(88)

(89)

(90)

(91)

(92)

(93)

(94)

(95)

(96)

(97) .

1952. ASSOCIATION OF SULFUR CONTENT WITH ACIDITY AND QUAUTY

IN DATES. Date Growers' Inst. Rpt. 29: 16-17.

1953. THE RELATION OF HIGH TEMPERATURES TO THE PREVALENCE OF

DRY-TEXTURED FRUIT IN THE DEGLET NOOR DATE

CROP. Handling, Transportation and Storage Off. Rpt. 300, 5

pp.

1954. RELATION OF DRY TEXTURE IN DEGLET NOOR DATES TO HIGH

SPRING TEMPERATURE. Date Growers' Inst Rpt. 31: 4-5.

1956. EFFECT OF TEMPERATURE AND MOISTURE CONTENT ON THE

RATE OF DETERIORATION IN DEGLET NOOR DATES. Date Growers' Inst. Rpt. 33: 8-11.

1957. RELATION OF MOISTURE CONTENT TO RATE OF DARKENING IN

DEGLET NOOR DATES. Date Growers' Inst. Rpt* 34: 12-13.

1958. INFLUENCE OF HANDUNG PROCEDURES AND STORAGE AND

TRANSIT TEMPERATURES ON IMPROVING AND MAINTAINING

QUALITY OF DATES. Date Growers' Inst. Rpt. 36: 2-5.

1963. EXPERIMENTAL STORAGE OF DATES IN BULK BINS. Date Growers' Inst. Rpt. 40: 8-9.

1971. OBSERVATIONS ON DEGLET NOOR DATE PRODUCTION IN ALGERIA. Date Growers' Inst. Rpt. 48: 12-13.
DATE DEVELOPMENT IN THE UNITED STATES 56

(98) RYGG, G. L.

1971. COMPARISON OF HEAT AT INDIO, CAUFORNÎA* WITH THAT AT

BISKRA AND TOUGGOURT, ALGERIA, AND THE ElTPECT ON DËGLET

NOOR DATE QUALITY. Date Growörs' Inst. Rpt, 48: 28.

(99) FURR, J. R., NixON, R. W., and ARMSTRONG, W. W.

1953. FACTORS AFFECTING THE SPOILAGE OF DATES AT ROOM TEMPERATURE. Date Growers' Inst. Rpt 80:10-14.

(100) SCHILLER, F. H., and MAIER, V. P.

1959. RESEARCH ON DATES AND DATE PRODUCTS. Date GroWeî^Ô*

Inst. Rpt. 86: 11-13.

(101) SHARPLES, G. C.

1953. A STUDY OF SPOILAGE AND THE MICROORGANISM POPULATION

OF SOFT DATES. Date Growers' Inst. Rpt. 30; 5-^.

(102) SHERMAN, H. C.

1946. CHEMISTRY OF FOOD AND NUTRITION. Ed. 7, 675 pp.» illus. NeW

York.

(103) SlEVERS. A. F., and BARGER, W. R.

1930. EXPERIMENTS ON THE PROCESS^G AND STORING OF DÈGLET

NOOR DATES IN CAUFORNÏA. U.S. Dept. Agr. Tech. BuL 193* 24

pp.

(104) SINCLAIR, W. B., BARTHOLOMEW, E. T., and BLISS, D. E.

1942. A COMPARISON OF THE COMMERCIAL GRADES OF DEGLET Ñ00R

DATES. Date Growers' Inst. Rpt. 19: 13-18.

(105) SLADE, H. B.

1906. DATE PALM FRUIT. Ariz. Agr. Expt. Sta. Rpt. 7: 164-166.

(106) SMITH, HUGH M., and NAVAS, NICíí.

1959. DISPLAYING DATES IN PACKAGES OF DIFFERENT SIZES. U^S.

Dept. of Agr. Agr. Market. Serv. AMS 349.

(107) SPOON, W.,

1957. [UTIUZATION OF DATE SYRUP AND DATE STONES.] Cacao-Choco*

lade Suikerwerkes 25: 340. (In Dutch.]

PRINTED FROM COCOA, CHOC. Suikerw 25: 340.

(108) STICKNEY, FENNER S., BARNES, DWIGHT F., and SIMMONS, PEREZ.

1950. DATE PALM INSECTS IN THE UNITED STATES. U.S. Depti Agfr.

Cir. 846, 57 pp.

(109) SWINGLE, L.

1926. COLD STORAGE OF DATES. Date Growers* Inst. Rpt. 3: 3-4.

(110) TuRRELL, F. M., SINCLAIR, W. B., and Buss, D. E.

1940. STRUCTURAL AND CHEMICAL FACTORS IN RELATION TO FUNGUS

SPOILAGE OF DATES. Date Gfowers' Inst. Rpt. 17: 5-11.

(111) VAUGHN, R. H., and OLSON, R. L.

1947. SUGGESTIONS FOR IMPROVjEMENT IN DATE PACKING 1?LANT SANITATION. Date Growers' trtst. Rpt. 24: 28-32.

(112) WINTER, F. H., and SMITH, E. E.

1948. CONTINUOUS SANITIZING OF EQUIPMENT IN THE DRIED FRUÍT

INDUSTRY. Food Technol. 2: 1-5.

(113) ViNSON, A. E.

1911. CHEMISTRY AND RIPENING OF THE DATE. Ariz. A^. Expt. Sta.

Bui. 66: 408^35.

(114) ViNSON, A. E.

1924. THE CHEMISTRY OF THE DATE. Date Gt*öWers* Inst. Rpt 1: 11-

12.
56 AGRICULTURE HANDBOOK 482, U.S. DEPT. OF AGRICULTURE

(115) WALKER, JACK, and MITCHELL, D. H.

1944, THE FUMIGATION OF DATES. Date Growers' Inst. Rpt. 21: 4-6.

(116) WHELTON, RITA, PHAFF, N. J., MRAK, E. M., and FISHER, C. D.

1946. CONTROL OF MICROBIOLOGICAL FOOD SPOILAGE BY FUMIGATION

WITH EFOXmES. Food Indus. 18: 23-25, 174-176, 318-320.

(117) WHITTLESEY, H. R.

1940. EFFECTS OF SULFURING AFTER RAIN. Date Growers' Inst. Rpt.

17: 16.

(118) YARWOOD, C. E.

1961. ACQUIRED TOLERANCE OF LEAVES TO HEAT. Science 134: 941-

942.

(119) YOST, LELAND J.

1940. OBSERVATIONS OF THE EFFECT OF RAIN ON KHADRAWI

DATES. Date Growers' Inst. Rpt. 17: 16.

T!^ U.S. GOVERNMENT PRINTING OFFICE: 1975 0—573-851