4"^

AGRICULTURE HANDBOOK NO. 159

UNITED STATES DEPARTMENT OF AGRICULTURE

AGRICULTURAL MARKETING SERVICE
BY

A. LLOYD RYALL AND JOHN M. HARVEY

AGRICULTURAL MARKETING SERVICE

AGRICULTURE HANDBOOK NO. 159

UNITED STATES DEPARTMENT OF AGRICULTURE

WASHINGTON, D.C. ISSUED JUNE 1959

For sale by the Suporintendont of Docuinents, U.S. Government Printing Oílicc

Washington 25, D.C. - Price 45 cents
CONTENTS

Page

Introduction 1

Factors affecting quality of stored

table grapes 2

Maturity 2

Handling before and during

storage 2

Precooling 2

Storage environment 8

Types of refrigeration systems 14

Dry-coil bunkers 14

Central brine-spray chambers-_ 18

Unit-coolers 19

Ice-refrigerated storages 19

Factors affecting refrigeration capacity requirements 22

Field h¿at 22

Vital heat 23

Heat leakage 24

Air infiltration 24

Other heat sources 25

Disorders of grapes in storage 25

Decay 25

Gray mold rot 25

Cladosporium rot 27

Alternaría rot 27

Other types of decay 27

Physiologic aging 27

Chemical injury 29

Freezing injury 29

Desiccation 29

Mechanical injury 30

Shatter 30

Bruising 31

Berry cracking _ 31

Fumigation with sulfur dioxide— 31

Methods of applying sulfur

dioxide 32

Fumigation with the liquefied Page

gas 32

Fumigation with bisulfite 33

Symptoms of sulfur dioxide

injury 34

Factors affecting sulfur dioxide

injury 35

Variety 35

Maturity 35

Fruit temperature 35

Wounding . 35

Concentration and length of

exposure to fumigant 36

Frequency of fumigation during storage 36

Precautions to follow when using

sulfur dioxide 37

Human toxicity 37

Injury to other commodities- 37

Corrosive effect on equipment 37

Other precautions, _ 37

Selective marketing of storage lots_ 38

Inspection in storage, _ - 39

Forecasting decay in storage

grapes 39

Method 39

Effect of harvest date 40

Effect of source of storage lot_ 40

Application of forecast 40

Literature cited - _ 41

Appendix 45

Calculation of the refrigeration

requirements of a theoretical plant 45

Plant design and operation 45

Refrigeration requirements, __ 45
THE COLD STORAGE OF

VINIFERA TABLE GRAPES

Â. Lloyd Ryall and John M. Harvey ^

Introduction

This handbook brings together

the accumulation of 30 years of research and experience in grape

storage. It is written for operators

of storage plants, growers, packers,

and buyers of fresh grapes. The

information presented on temperature, humidity, air movement, storage design, fumigation, and storage

disorders, together with the sources

of such information, can be used to

maintain quality, reduce spoilage,

and improve marketing of grapes.

Although European-type table

grapes {Vitis vinifera L.) have

been produced commercially in California since 1860, {36, 64) ' prolonged storage dates back only to

the late 1920's when methods for

periodic fumigation with sulfur dioxide were developed. Before this

some table grapes were packed in

ground cork or sawdust and were

stored for only 4 to 6 weks, mostly

at terminal markets (70), With

further development and refinement of fumigation methods, the

extensive storage of grapes in display lugs became possible and increasing quantities were stored in

^ A. L. RyaU is a horticulturist, QuaUty

Maintenance and Improvement Section,

Biological Sciences Branch, Marketing

Research Division, Agricultural Marketing Service, Beltsville, Md. J. M. Harvey

is a plant pathologist, Quality Maintenance and Improvement Laboratory,

Fresno, Calif.

^ Italicized numbers in parenthesis

refer to items in Literature Cited, p. 41.

the producing areas for distribution

during the winter and spring

months.

The holdings of table grapes in

California during 4 representative

storage seasons from 1935 to 1955

are shown in figure 1. During this

period table grape production was

fairly constant and yet, as the figure shows, both the quantity of

fruit stored in California and the

Neg. BN-7103

Figure 1.-—Cold storage holdings of table

grapes in California during four seasons.

Data from annual summaries of FederalState Market News Service.
period during which it Avas stored

increased materially. During 1956

grapes were stored in about 95 cold

storages in California, many of

which, particularly in the San

Joaquin and Sacramento Valleys,

are designed principally for table

grapes. On November 15, 1955,

about 6,500 carlots of table grapes

were in Central Valley storages.

Factors Affecting Quality of Stored Table Grapes

Each of the characters that contribute to dessert quality, such as

flavor, color, and texture, is at a

peak when grapes are harvested at

optimum maturity. Changes that

occur thereafter, even under ideal

holding conditions, involve a gradual deterioration of these qualities.

It is thus apparent that good quality after storage depends primarily

on placing fruit of good quality

into storage.

Maturity

The determination of optinmm

maturity of table gra})es to be

stored should be based on such qualities as berry and stem color, sugar

content, acidity, and development

of flavor characteristic of the variety. Minimum legal maturity for

shipment under California law is

based almost entirely on soluble

solids as determined by juice readings with iJie Balling hydrometer

or hand refractometer. However,

Winkler (76) found that the ratio

of soluble solids to percent acidity

of the expressed juice was a better

index of dessert quality than soluble

solids alone and suggested Ballingacid ratios for table varieties tluit

were above the legal minimum but

below 20 percent soluble solids.

Grapes Avith 20 ])ercent or more

soluble solids were considered to

have good dessert quality at any

acidity level.

As grapes mature the stems

change from a leaf-green to a light

green or straw color, and in some

varieties a woody portion resembling the cane forms at the base of

the stem. These clian<>:es are indicative of good storage quality, for

matured stems are less subject to

desiccation, breakage, discoloration,

and mold attack than immature

ones. In addition, well matured

stems are usually indicative of well

matured and colored berries. The

sturdy cap stems (pedicels) characteristic of matured stems reduce

the shatter of berries from the

cluster.

Handling Before and During

Storage

Precooling

The value of prompt and thorough removal of field heat from

grapes intended for immediate

shi})ment or storage has been demonstrated re})eatedly in both controlled tests and industry experience. Fruit sliould not only be

])romptly cooled after Packing, but

unnecessary delays in the Anneyard

and packing house before trinnning

and packing should be avoided.

Delays at high temperature betAveen harvest and the start of pre-

(H)oling are certain to result in undesirable stem drying, berry

shrivel, shatter, and infection by decay organisms (.^2).

Relation to Moisture Loss From Fruit

Loss of Avater from any product

is governed largely by the proteetÍA^e surface of the commodity, the

amount of air moving over it, and

the difference in vapor pressure betAveen the commodity and the air.

Grape berries have a relatiA^ely impervious skin so they do not give

up Avater readily, and consequently
moisture is lost largely through the

stems.

Air movement may vary from

moderate in the vineyard to high

velocity during precooling. The

principal factor involved in moisture loss, however, is vapor pressure

differential. For example, if we

assume that air in the intercellular

spaces is nearly saturated witli

water vapor, the tissues at 80° F.

would have a vapor pressure equivalent to .99 inch of mercury. It

would be somewhat less than this

because of the sugar content of the

fruit, but these figures are valid for

comparative purposes. Air at 80°

with 20 percent relative liumidity

(RH) would have a vapor pressure

of only 0.21 inch. At 90° the tissues would have a vapor pressure of

about 1.3 while air at 90° with 22

percent RH would have a vapor

pressure of 0.30. These large differences in vapoi* pressure would result in relatively rapid movement of

moisture from the tissues to the air

and are representative of actual

conditions that might occur in the

vineyard or packing house after

picking.

Differences in vapor pressure

also occur during |)recooling because

low temperature air has a much

lower vapor pressure than high

temperature fruit (table 1). For

example, air at 31° F. and 94.3 ])ercent RH has a vapor pressure of

0.164 inch whereas grapes at 80°

have a vapor pressure of about 0.99.

From these figures it is apparent

that the faster grapes can be lowered to the temperature of the air

in the precooling chamber the less

moisture will be lost. The figures

in table 1 also demonstrate that

maintaining high atmospheric

humidity during precooling is not

as important as fast cooling. To

illustrate this fact, observe that the

difference in vapor pressure of 31°

air at 94.3 percent RH and 79.5

percent RH is insignificant as compared with the vapor pressure of

fruit at higher temperatures. This

principle was demonstrated by

Dewey (IS) in a study of moistureloss from cherry and grape stems.

He found that significantly more

water was lost from sweet cherry

stems cooled in still air at 90 percent RH than in an air blast at 70

percent RH. The amount of cooling that took place in 1 hour in an

air blast required over 7 hours in

still air. Consequently, the difference in moisture-loss was due primarily to the rapid decrease in

vapor pressure differential when

subjected to air blast cooling.

TABLE 1.—-Relation of air temperatn^re ar\d relative liumidity to

vapor pressure

Air Depres- Rela- Vapor

tempera- sion of tive hu- presture wet bulb midity sure (Hg)

(dry buU))

°F. ""F, Percent Inches

31 0.5 94.3 0. 164

31 2. 0 79. 5 . 136

32 . 5 94. 4 . 172

32 2. 0 80.0 . 143

33 . 5 94. 5 . 180

33 2. 0 80. 5 . 150

34 . 5 94. 6 . 187

34 2. 0 81. 0 . 157

35 1. 0 90. 0 . 187

40 1. 0 92. 0 . 228

50 . 5 96. 0 . 347

60 . 5 97. 0 . 499

70 . 5 98. 0 . 707

80 . 5 98.0 . 989

80 23. 0 20. 0 . 322

90 1. 0 96. 0 1.364

90 22. 0 31. 0 . 432

90_ 29. 0 15. 0 . 211

Factors Affecting Rate of Precooling

The rate of cooling of any commodity is primarily dependent upon

four factors: (1) The accessibility

of the product to the refrigerating

medium, (2) the difference in temperature between the product and

the refrigerating medium, (3) the

velocity of the refrigerating me-
dium, and (4) the kind of coolingmedium. Since air is the refrigerating medium used in grape cooling

to obtain optimum cooling, (1)

the product must be packaged and

stowed in such a way that air will

reach all packages of fruit uniformly, (2) the temperature of the

air must be maintained continuously at a point slightly above that

at which the product freezes, and

(3) the air must be moved rapidly

over, or preferably through, the

containers.

Effect of packaging.—Accessibility of the product to the coolingmedium is one of the factors governing the rate of cooling. Since

the type of package and the materials used in the package affect

accessibility, they become factors in

tlie cooling rate. Pentzer (60) reported that grapes packed in sawdust cooled at about half the rate

of grapes in the display lug. He

also showed that cellophane curtains over the face of the pack considerably reduced the cooling rate

over that in lugs without curtains.

However, this difference in coolingrate occurred only when both types

of pack were exposed to circulating

air. In parts of the load wiiere

cooling was principally by conduction the curtains had little effect.

%all {62) reported that, under

standardized conditions of air

movement, the cooling rate in

standard display lugs was affected

by placement of the side slats, and

that either side liners or curtains

reduced the cooling rate as compared with lugs packed with bottom pads only. When the grapes

can be stored under ideal conditions

after precooling (about 90 percent

RH and minimum air movement

for the maintenance of uniform

temperatures), packaging materials, other than bottom pads, are of

questionable value. Their elimination would reduce packing costs and

speed precooling. However, when

grapes are stored under lower than

recommended liumidities or excessive air movement, such materials

as side liners or curtains may be

justified for the reduction of stem

drying and berry shrivel.

Types of Precooling

Room precooling,—Many of the

table grapes going into cold storage

are precooled in special rooms that

have more refrigerating capacity

and greater air volume than tlie

regular rooms in which the grapes

are stored. These rooms are generally rather small with capacities

of from 1,000 to 5,000 lugs, so that

they can be filled rather rapidly and

operated witliout interruption during the cool iug period. Since it requires approximately 4 tons of refrigeration to cool 1,000 lugs of

grapes 40°, a room that holds 2,000

higs with capacity to reduce this

load 40'' in 12 hours must be

equipped to provide 16 tons of refrigeration in 24 hours. Additionally, it should have fans or

blowers capable of producing 6,000

to 8,000 cubic feet per minute (cfm)

of air per 1,000 lugs of fruit and

air directing or distributing devices

that will provide an even flow of

air in all parts of the room.

Figure 2 shows a dry-coil bunker

precooling room with 2 of the

baffles removed to show the coils.

The 2 fans pull air over the refrigerating coils (7,900 feet of 114-

inch ammonia coil) and move it

through a duct on the ceiling to the

back of the room where it is released. The air returns through

the palletized stacks to the bottom

opening of the coil bunker. The

room has a capacity of 5,200 standard display lugs (28 pounds net)

and the 2 blowers move air at 34,600

c.f.m. This is an excellent type of

precooling room with ample refrigeration and good air volume

and distribution.
BN-7104

Figure 2.—Face of dry coil bunker 12 panels

removed) and ducts from two fans. Fivecar precooling room.

A precooling room refrigerated

by a central brine spray vinit is

shown in figure 3. Air is ducted

from the spray unit to the back end

of the room and passes into a return

duct through the openings shown

at the front. The room has a capacity of 2,200 hand-stacked lugs. Additional air as needed can be

diverted from the main supply duct.

The vertical flue in one comer is

used to circulate sulfur dioxide

during fumigation which, at the

completion of gassing, can be

cleared from the room by manipulation of the louver.

An ice-refrigerated precooling

room with a capacity of 6,600 lugs

in one layer of pallets is shown in

figure 4. Six fans, each with a

rated capacity of 8,000 c.f.m., are

located at the top of the bulkhead

in the far end of the room. These

Figure 3.—A 2,000-lug precooling room with air ducted from central brine spray chamber—opening to return duct and SO2 circulating flue shown.
Figure 4.—Ice-refrigerated precooling room sliowing false ceiling for dueling air from six fans

and canvas baffles for directing air through palletized stacks of fruit.

])iill iiir from an ice bunker located

below the loadirif^ platform outside

the buildiiifi, move the air through

the false ceiling duct, and discharge

it near the rear of the room. When

the room is operating, the canvas

baffles suspended from the duct are

lowered to the top of the load to

assure movement of the return air

through the stacked fruit rather

than over the top of the load. The

bunker has a capacity of about 30

tons of chunk ice to which salt can

be added if a lower temperature air

blast is desired. In actual operation the generous air volume and

liirge ice capacity of this system

have provided a satisfactory rate of

cooling without the use of salt.

Car precooling.—G rapes intended for storage are not ordinarily precooled in refrigerator

cars. However, when gra]>es move

some distance to a cold storage

])lant from y)oints where other ])recooling facilities are not available,

very satisfactory removal of ñeld

lieat can be accom])lislied in a

I'efrigerator car. In this case the

refrigeration is supplied by ice in

the car bunkers and the air movement is provided by either the builtin car fans or portable bulkhead

fans. The refrigerator car thus becomes essentially a precooling room

and the same principles of air

volume, air direction, and temperature differential apply. The fruit

must be loaded to provide free air

access to all parts of the load, the

bunkers must be ke])t adequately

su]>plied with ice, and salt must be

added to the ice in sufficient amount

to maintain a consistently low air

blast tem]ierature.

Forced air precooling.—A method of rapid cooling, based on fore-
ing air through vented containers

by creating a pressure differential,

has been developed by the Department of Agricultural Engineering

atthe University of California (26),

It has been reported that commodities packed in containers that allow

free air flow through the package,

and in stacks spaced and baffled so

that air supplied by the fans must

pass through the packages, can be

cooled in one-eighth the time required by the conventional method

of passing air over the outer surfaces of the packages (fig. 5).

To reed-Air Truit Cooler

Dia^rarr2rT2Atic Section

BN-7107

Figure 5.—Principle of forced-air cooling.

(Photograph courtesy of Rene Guillou, Department of Agricultural Engineering, University of California, Davis, Calif.)

Other adaptations of this principle can and have been successfully

made in existing precooling rooms

and in refrigerator cars. Plowever,

it should be remembered that the

system is ineffective with any pack

that does not permit air passage,

such as a wrap pack or sawdust

pack, and it becomes less effective

as resistance within the package is

increased by packaging materials

such as side liners, curtains, trays,

or cups.

Tunnel cooling,—Tunnel coolinghas been used for several years in

the early grape districts (i) for

the rapid removal of field heat from

packed grapes. The method allows

the loading and shipment of precooled grapes on the day of harvest

whereas conventional cooling methods require holding the fruit over

a day to accomplish comparable

cooling. However, tunnel cooling

also has been used for rapid precooling prior to refrigerated storage. The cooling is accomplished

by moving the packed, unlidded

lugs on a continuous conveyor

under a plenum chamber from

which high-velocity, refrigerated

air is directed at the face of the

lugs from slots on the lower face

of the plenum. The refrigeration

source through which the air circulates is either ice or a mechanically refrigerated evaporator coil.

Some of the units are designed to

move a single layer of lugs directly

under the plenum whereas others

use multiple layer conveyors with

baffles beneath each row of lugs to

redirect the air at the face of the

lugs below. The single layer coolers have produced somewhat more

rapid and uniform cooling than the

multiple layer coolers. Figure 6

illustrates the loading end of a

multiple layer cooler operated in

the Coachella Valley.

Yacumn cooling.—The cooling of

certain kinds of fresh produce by

evaporation of moisture at reduced

pressures obtainable in a vacuum

chamber has developed into extensive commercial use within the last

8 years. However, the process is

adapted principally to those commodities, such as leafy vegetables,

that have a relatively large surface

area in proportion to volume. The

amount of heat that can be removed by this process is limited by

the amount of water than can be

vaporized from the tissues without

497396°—59-
1ÎN-710S

Figure 6.—Multiple-layer tunnel cooler. (Photograph courtesy of California Fruit Exchange, Sacramento, Calif.)

damage to the texture or appearance of the product.

Tests conducted at Fresno and

New York {^4) have shown individual grape berry temperature reductions of only 6° to 10° by the

standard treatment used for leafy

vegetables. W. R. Barger of the

U.S. Department of Agriculture

(unpublished data) determined

that moisture loss from grape

clusters was only 0.4 to 0.5 percent

when pressure in the chamber was

reduced to 4.5 mm. of mercury and

maintained for 10 minutes. Cooling from 70° to 35° F. would require evaporation of water equivalent to approximately 2.5 percent of

the original fresh weight of the

fruit. If it were possible to withdraw this amount of moisture the

appearance of the clusters would

probably be adversely affected. It

seems apparent, therefore, that

grapes are not adapted to vacuum

cooling.

Storage Environment

After sound, mature grapes have

been properly packaged and precooled, the factor which then determines success or failure in their

preservation is the storage environment. Factors in the environment

that affect grape quality are temperature, atmospheric humidity,

air movement, and fimiigation with

sulfur dioxide.

Temperature

Although one study (12) indicated that Emperor grapes could be

stored at temperatures as low as

28.4° F., present recommendations

are generally for air temperatures

8
of 30° to 31°. The freezing point

of seven varieties of Californiagrown vinifera grapes has been reported to vary from an average of

23.6° and a range of from 22.9° to

24.7° for mature Thompson Seedless, to an average of 25.6° and a

range of from 25.2° to 26.1° for mature Almeria (78), Since the

freezing point is largely determined

by sugar content, certain lots that

are harvested at minimum maturity

may have freezing points as high as

27°. While there appears to be no

evidence on the freezing point of

grape stems, it seems probable that

they may freeze at a slightly higher

temperature than the berries. To

provide a margin of safety in relation to freezing, allowance niust be

made for temperature variation because of the lag in response to refrigeration controls and the temperature spread between incoming

and return air.

Relative Humidity

A numerical figure for relative

humidity represents the percent of

saturation of air Avith water vapor

at a given temperature. The water

liolding capacity of air increases as

the temperature rises so air of 90

percent relative humidity at 70° F.

contains much more water by

weight than air of the same relative humidity at 32°. As the relative humidity of air increases the

vapor pressure also increases and

the capacity of the air for removinp- water from other sources

decreases.

It is thus apparent that to reduce

moisture loss from stored fruit to a

minimum, the relative humidity of

the storage air must approach that

of the air within the intercellular

spaces of the individual fruits. Assuming that air in the intercellular

spaces is saturated and that the

fruit and storage air temperatures

are identical, moisture loss from the

fruit could be entirely stopped only

by maintaining the storage air at a

relative humidity of 100 percent.

However, this is not possible under

commercial conditions and would

not be desirable if it could be accomplished because saturated air

would favor the rapid development

of decay organisms. Actually, the

relatively small vapor pressure differential between fruit at 32° F.

and air at 31° with 90 percent RH

results in only slight moisture loss

from the product. Such slight

losses are within the limits of commercial acceptibility during a normal storage period, particularly if

air movement is not excessive. It

has been determined that grapes

can lose as much as 1.2 percent

water by weight without affecting

their appearance and that moisture

losses as high as 5 to 6 percent were

required to cause severe shriveling (4^).

The best and currently recommended relative humidity for the

cold storage of vinifera grapes is

87 to 92 percent (S), Earlier

recommendations were usually in

the range of 85 to 90 percent, but

as methods of decay control have

been improved the use of higher

humidities, as a means of maintaining better appearance, has been

recommended and rather generally

accepted.

Accurate control of refrigerant

temperature provides the only satisfactory method for maintaining

high humidities in mechanically

refrigerated storages. As the difference between the temperature of

the refrigerating surface (coil or

spray) and the temperature of the

air in contact with the refrigerating

surface increases, the humidity decreases. If the temperature of the

refrigerating surface is below the

dew point at a given air temperature

and relative humidity, then moisture will condense on this surface

and the air will lose moisture equivalent to the amount condensed.
Air temperature

(dry bulb)

F.

29

29

29

30

:^o

30

31

31

31

32

32

32

33

34

35

Depression

of wet

bulb

"" F.

0. 5

1. 0

2. 0

0. 5

1.0

2. 0

0. 5

1. 0

2. 0

0. 5

1. 0

2. 0

I. 0

1. 0

1. 0

Relative

humidity

Percent

94. 1

88. 3

78. 5

94. 2

88. 6

79. 0

94. 3

89. 0

79. 5

94. 4

89. 2

80. 0

89. 5

89. 7

90. 0

The data in table 2 indicate the this is a makesliift which will marelative humidity that could be terially add to coil frosting or brine

expected wdth certain air and re- dilution problems,

frigerating surface temperatures.

For example, if the air moving over TABLE 2.—Relation of dew point to

the refrigerating surface is cooled air temperature and relative

to 30° F. and the surface tempera- humidity

ture is 25°, the relative humidity of

this air will be about 79 percent

because any water vapor above this Dew

amount will condense on the coil or point

spray. However, if air at the same

temperature moves over a refrigerating surface maintained at 27° "" F

the relative humidity will be almost ,^^

89 percent and if the difference be- 23

tween air and refrigerant tempera- 29" ~_

ture were only 1° (air 80°, refrig- 27

erant 29°) then a relative humidity ^^^

of over 94 percent could be expected. 28

Actual humidities obtained under 26

the above conditions of refrigerant ;^l

and air temperatures will usually 27

be somewhat higher than indicated 31]""]

because all of the air will not come 32

in contact with the refrigerating '^'^

surface. Thus air leaving the

chamber will be a blend of that ^ . „ . ^ which has dropped moisture and , ^n ice-refrigeratp.d storage rooms

that which has retained its original í^^^' temperature of the refrigerant

moisture content. !^ '^^ ,^. • ^^^^^^^^ ^^^^ '^ added to the

It is, of course, apparent that as ''^' Air temperatures m well dethe split between refrigerant temp- ^^^^^^^ ice-refrigerated storages

erature and air temperature be- ufJ^^Hy can be maintained at about

comes narrower, a greater refrig- '^^ , ,\J^}^ ^'*'V^. '^ thoroughly

erating surface is necessary. Tf a^r ^'?^1^^- Tf.'}}"'} refrigerant temperis cooled from 82° to 80° F. during '^^^""^ ^^^/'^ ^}^^ ^T^^ indicate a

passage through a dry coil bunker, I'elative humidity of about 90 perconsiderably more surface will be ^^^^^ which is well withm the desirrequired to accomplish this temp- ^^ble range. As with mechanically

erature reduction when the coil is refrigerated rooms the amount of

operated at 29° than when it is refrigerating surface is important

operated at 25°. This principle has and if 84° air is to be maintained,

been recognized in most of the with melting ice at 32° as the renewer grape storage plants. With frigerant, an ice bunker large

an adequate refrigerating surface enough to permit a large ice surface

and with the temperature of that must be provided,

surface controlled by automatic

devices, there is no humidity prob- ^^^ Movement

lem. Where refrigerant surface is As indicated in an earlier section,

not adequate to maintain the desired to provide uniform high velocity

atmospheric humidity, pressure- air through the stacks, a minimum

atomized or heat-vaporized water air volume of 6,000 c.f.m. per 1,000

can be added to the air. However, lugs is essential for the rapid re10
moval of field heat. This Is best accomplished in a separate precoolin^

room that has more refriiterating

and air movinji capacity tlian that

required in a regular liolding room.

After the field heat has been removed from the fruit, a high air

velocity is unnecessary and undesirable. Only enough air movement

should be provided to remove respiratory heat and heat entering the

room through exterior surfaces and

doorways. Usually 50 to 75 linear

feet per minute (lfm) through the

stacks is sufficient to accomplish

this, but it is very important that

the air is directed in such a way that

it moves uniformly throtigh all

parts of the room. Allen and Pentzer (f¿) found that doubling the air

movement in fruit storage rooms increased moisture loss by about onethird and was equivalent to about a

5 percent drop in relative humidity.

Methods of controlling air movement.—All modern grape storage

rooms have fans or blowers to provide forced air circulation. The

rooms, with individual dry-coil,

spray-coil, or ice bunkers, provide

air movement by means of blade

fans mounted along the upper part

of the bunker. These may move air

directly across the upper part of the

room from open fans (fig. 7) or

through ducts which extend part

way or entirely across the ceiling to

discharge air against or down the

opposite wall (fig. 8). Somewhat

more positive and uniform aii'

movement is obtained when the air

is ducted across the room to return

through the stacked fruit than

when open fans are used. With the

latter there is a tendency for part of

the air to short-circuit back to the

bunker.

Many methods of air circulation

are used within rooms wliich are

cooled by a ducted system from a

central brine-spray chamber. A

common system for distributing air

in the nai-rower rooms is shown in

figure 9. Each long wall of the

room contains an air duct. The air

from the brine spray chamber is

discharged through the louvered

openings at the lower part of the

right wall, moves through the

stacked fruit and enters the return

duct through openings located

along the wall and near the ceiling

at the left. If the openings are

properly adjusted to effect uniform

air flow from the discharge side, this

system provides very uniform and

satisfactory air movement.

In wider rooms multiple ducts are

often used. The air is discharged

from several ducts and moves in a

predetermined pattern to one or

more retui'n ducts. Figui'e 10

shows a grape storage room in

which the air from the central brine

spray chamber is discharged downward from a duct on each side wall,

moves through the stacks to the

center of the room, and enters the

return duct through openings at the

bottom and upper sides. This provides excellent air distribution as

determined by the uniformity of

air velocity and temperature

through the room.

0 • ]I

iî . l ! Il ii ii

tí I'l I'l i Ï Ï i

:i—.. ,. i ..,, t,. . 11

! î \ \ j

" -'"^»"^m•

BN-7n)ll

Figure 7.—Open fan at the top of a dry-coil

bunker.

n
t .„>

^^^^^^^^^

-s:=r^=î^ -P^%'-*:í^^S^ "=?^ï--5^^t "í^^

y '•^>W

-f-T—-î?r

BN-711Ü

Figure 8.—Rear wall discharge of air from ceiling ducts in room dry-coil bunker system. Air

moves straight down from bottom duct openings and straight out from front duct openings.

JîiN-7111

Figure 9.—Cross-room air movement from wall ducts supplied by central brine-spray chamber.

Air moves across room from louvered openings at right to upper and lower openings at left.

12
f

BX-7112

Figure 10.—Storage room with air discharge ducts at side walls and return duct in center. Air

moves down from bottom of side wall ducts and up into bottom and sides of ducts down center

of room.

Ejfect of utacking method on air

moveinent.—^Air distribution and

fruit temperature are both materially affected by placement and

alignment of the stacked packages

of fruit. Most of the newer plants

stack on pallets with the pallet

loads placed 3 high in the storage

rooms. Whether the container's are

palletized or hand stacked in the

rooms, 2 principles should be observed: (1) The side of the display

lugs should be in the direction of

air movement; and (2) uniform

spacing should be maintained between rows and between pallets.

Heat transfer is accomplished much

more easily from the lightweight,

partially open side of the lug than

from the thick, solid end pieces;

and uniform spacing of rows and

pallets is essential for good air distribution.

A cardinal principle of air movement is that air will follow the

path of least resistance and, if spacing is irregular, the wider spaces

will get a greater volume of air

than the narrower ones. If some

spaces are partially blocked, dead

air zones will occur with resultant

temperature rises or localized failure of sulfur dioxide to reach these

spots during fumigation. Wide

aisles in the direction of air movement are undesirable since most of

the air will move through the aisle

and will by-pass the stacked fruit.

If two-way pallets are used the

pallets can be stacked in either direction, but when one-way pallets

are used the open ends should always be in the direction of air movement. Figures 11 and 12 illustrate

excellent stacking arrangements for

13
¡¡**vV^;

HN-71l:i

Figure 11.—Palletized stacks on two-way pallets with sides of lugs in direction of air movement.

palletized fruit. Figure 11 shows

fruit on two-way pallets with good

spacing between rows on the pallets

aiid between pallets. Air is discharged from the duct at the back

of the room and moves forward to

the coil-bunker through the stacks.

This room was being emptied when

the photograph was made, but is

completely filled during most of the

storage season with an aisle only

along the coil-bunker side of the

end crosswise of the air movement.

Figure 12 shows the face of palletized stacks in a coil-bunker room

with open fans. Air from the fans

moves over the top of the stacks

and returns through the stacks to

the bottom bunker opening. These

are one-way pallets with tlie open

ends in the direction of air movement. Note the unifoi'm spacing

of lugs and pallets and the excellent

alignment.

Types of Refrigeration

Systems

Many cold storage plants in

Central California were designed

and built specifically for the storage

of table grapes. In these plants,

four general types of refrigerating

systems exist : ( 1 ) Individual room

dry-coil bunkers; (2) individual

room unit coolers; (3) central

brine-spray chambers with ductedair systems; and (4) individual

room ice bunkers. There are however, many minor variations within these basic types.

Dry-Coil Bunkers

Most cold storages built in recent

years and intended primarily for

table grapes are of the individual

room, dry-coil bimker type. Directexpansion coils of smooth pipe

14
(usually 114 to 2 inch) are mounted

on one wall of the room and a

wooden baffle is constructed between

the bank of coils and the room.

Openings at the top and bottom of

the baffle allow air to circulate over

the coils. Fans in the upper

openings draw the air in at the

bottom opening ; the air moves over

the refrigerating surface on the coil

bank and through the fans to ceiling ducts or directly into the space

above the stacked produce.

It is customary to place the coil

bunker on the long-dimension wall.

If the room is not over 40 feet wide,

open fans at the top of the baffle

generally provide satisfactory air

distribution. If the air must be

moved more than 40 feet, better air

distribution is obtained by moving

the air through ducts part or all the

way acrossthe room.

This system is particularly well

adapted to grape storages because

grapes must be treated periodically

with sulfur dioxide and the individual room bunker permits each

room to be treated as a separate

unit. Since sulfur dioxide is rather

corrosive to metals, smooth pipe

rather than finned coils are used.

The coil surfaces are often coated

with corrosion-resistant paints, and

some method of bypassing the coil

during sulfur dioxide fumigation is

commonly provided. Figure 13

shows a section of dry-coil bunker

during normal refrigeration operation with the louvers at the bottom

of the baffle open for air circulation through the coil bank. The

same section is shown in figure 14,

but with the bottom louvers closed

and the hinged door near the fan

housing open. This permits cirFigure 12.—Palletized stacks on one-way pallets. Air movement along sides of lugs and open

pallets.

497396°—59- 15
BN-7117

Figure 13.—Section of dry-coil bunker with fan above and bottom louvers open for air circulation

tlirough the coil bank.

culation ofsulfur dioxide within the

room, while avoiding direct contact of the circulating gas with the

coils. However, some of the gas

reaches the coils by diffusion and

even after the room atmosphere is

cleared and normal air circulation

is resumed, some sulfur dioxide will

be present in the air as a result of

a gradual release of the fumigant

from the fruit and containers.

Unless the coils and supports are

thoroughly protected by an acid-resistant coating, it is desirable to

provide some means of washing the

coils after each fumigation. This

can be done by means of a water line

placed above the coils with spray

nozzles at suitable intervals. At the

completion of gassing, the ammonia

supply to the coil is shut oiï and the

water valve is opened. Since sulfur

dioxide is rather soluble in water

the room atmosphere can be cleared

rather eifectively, with the fans in

operation, while the water is flooding down over the coils. At the

same time the coils are defrosted

and any residual sulfurons acid on

the coils is washed away. Figure

15 shows a section of coil bunker

with three panels removed to reveal

water from overhead nozzles flooding over the coils during the degassing and defrosting period,

usually, somewhat less than 1 hour

is required for satisfactory removal

of sulfur dioxide from the atmosphere and thorough washing of the

coils. Because grapes are usually

stored at temperatures slightly below the freezing point of water it

is essential that means be provided

for draining all water lines in the

bunkers at the completion of the

washing process.

16
BN-7118

Figure 14.—Section of dry-coil bunker with bottom louvers closed and door above coils open for

bypass during sulfur dioxide fumigation.

BN-7110

Figure 15.—Section of dry-coil bunker with three panels removed to show water from overhead

nozzles during degassing and defrosting.

17
The removal of sulfur dioxide

from the storage room atmosphere

at the completion of fumigation is

accomplished by aeration in those

plants that do not have coil washing

equipment. In dry-coil bunker

rooms the usual arrangement involves a small door at the end of

the bunker which opens to the outside. When fumigation is completed this door is opened and outside air is pulled through the bunker

and forced into the room by the

fans. This builds up some air pressure in the room so that when a

room door is partly opened air

rushes out of the room. With the

usual fan capacity this method will

effectively clear a room in 30 to 40

minutes. Of course, some refrigeration is lost by moving outside air

into and through the room, but the

air does move over the coil before

it goes into the room.

Another method sometimes used

involves exhausting the air from the

room through a flue in the roof.

The flue has a built-in fan which,

when the flue louver is open, draws

air from the room. After the exhaust fan is started an outside door

is opened slightly so that a flow of

air through the room can be established. With an adequate fan capacity the clearing can be accomplished rapidly, but moving outside

air over the fruit during warm

weather often causes some condensation of moisture on the fruit and

containers. When either method of

aeration clearing is used the fumigation and degassing should be done

during the night to take advantage

of the lower outside temperatures.

Central Brine-Spray Chambers

Many of the older, and a few of

the newer cold storages in central

California are built with a centrally located brine-spray chamber

and blower. The chamber consists

of an enclosed bank of direct-expansion ammonia coils which are

continually being sprayed with a

solution or salt in water. Very effective heat transfer is obtained by

moving the air through the fine

spray of chilled brine. The cooled

air is distributed to the storage

rooms by duct systems such as those

illustrated in figures 9 and 10.

The central brine-spray chamber

requires substantially less ammonia

coil, less liquid and suction line,

and fewer control valves than the

individual room dry-coil bunker

system, resulting in a relatively low

original cost. However, effective

eliminators must be used on the air

discharge side of the brine chamber

to prevent particles of brine from

being carried in the air to the storage rooms. In grape storage rooms

it is necessary to neutralize the

brine with sodium hydroxide after

each sulfur dioxide fumigation.

Equipment for determining the hydrogen-ion concentration of the

brine should be used and the pH

should be maintained in a range of

7.5 to 8 continuously. Usually

the brine is also treated with corrosion-preventive chemicals as recommended by the manufacturer. The

principal disadvantages of the

ducted brine-spray system as applied to grape storages are (1) that

it is usually impossible to fumigate

a single room because all of the

rooms are served by one main air

supply duct and one return air

duct; (2) that total air volume is

usually less from the central blower

than from the multiple fans used

in the individual room systems ; and

(3) that uniform air distribution

is difficult to attain because of variations in air pressure and velocity

in different parts of the supply

duct.

It is a commonly held, but erroneous, belief that a brine spray,

18
when used for cooling, adds humidity to the air. On the contrary,

the brine spray picks up moisture

from the air to an even greater extent than a frosted coil due to the

somewhat lower vapor pressure of

brine at comparable temperatures.

Wile and Halls {7Ji) state that if a

brine-spray and dry-coil system operate at the same surface temperature the humidity must be lower

with the brine system. Thus, it is

essential for maintenance of proper

humidity that sufficient coil and

brine surface be supplied to maintain a minimum split between refrigerant and air temperature.

As mentioned previously, it is

usually impractical to fumigate a

single room in a multiple-room

plant with a central brine-spray

system. Therefore, the whole plant

must be fumigated as a unit, using

the central blower to circulate the

sulfur dioxide. The brine spray is

turned off during the fumigation

and clearing period, but even with

the spray off the brine and coils become acidified if circulation is

through the spray chamber. Accordingly, it is desirable to bypass

the air around the brine-spray

chamber during the gassing and

aeration periods. This can be accomplished with a special tunnel

around the spray chamber which

has suitable louvers for diversion

of the air through it when needed.

Clearing sulfur dioxide from the

storage air is often difficult in the

central brine-spray system. If an

outside door into the return air

duct is provided and an outside

storage room door opened at the

other extreme of the system, clearing can be accomplished reasonably

well.

Unit-Coolers

The unit-cooler is a modification

of the brine-spray or dry-coil

bunker systems in which the unit

contains expansion coils and blowers for moving the air through the

coils and discharging it into the

room. These may be in the form

of relatively small units suspended

from the ceiling or large units

placed along one wall. These generally have finned coils for extended

refrigerating surface and move the

air from open fans without ducts.

They are usually dry-coil units

although some of the larger wall

units have built-in brine spray systems. Unit-coolers are not commonly used in grape storage rooms,

principally because finned-coils

have a limited life when exposed

periodically to sulfur dioxide.

When such units are used there is

a tendency to use too few of them

for the maintenance of adequate

humidity and air movement. However, there seems to be no reason

why unit-coolers should not provide satisfactory conditions for

grape storage if the installation is

designed to provide adequate refrigerating surface and air volume.

Ice-Refrigerated Storages

Where the storage need is limited

to one or two seasonal commodities,

with a storage period of only a few

months, there has been an increasing tendency to use ice as a source

of refrigeration rather than mechanical systems. This is particularly true of storage plants owned

by growers who are interested in

having precooling facilities available during the harvest season and

in storing a limited quantity of

fruit for sale during the fall or

early winter.

A number of ice-refrigerated

storages are in operation in central

California. Capacities vary from

4,000 to more than 100,000 lugs of

grapes and construction varies from

19
those in which the lugs are handtrucked and stacked, to those with

mechanized handling operations

and ceiling heights which permit

stacking three pallets high. The

usual design is similar to that of the

individual room dry-coil bunker

system, with an ice bunker extending the full length of one wall and

fans at the top of the bunker or

bunker duct for discharging air

into the room. In some cases the

bunker is above ground and against

the outside of the room. More commonly the bunker is under ground

with the loading platform outside

the building at its upper surface.

This simplifies icing of the bunker,

for hatches in the platform are

readily accessible and the ice can

be handled at truck-bed level. Figure 16 shows the hatches (some open

with plugs removed) along the loading platform of an ice-refrigerated

storage plant which has underground bunkers.

BN-7120

Figure 16.—Icing hatches for bunkers of ice-refrigerated storage. Bunkers below platform

have capacity for about 184 tons of chunk

ice.

The first essential of an ice refrigerated plant is adequate bunker

capacity. There must be enough ice

surface to provide air near 32° F

at the discharge points and the volume of the bunkers must be such

that the air will not be restricted

during passage through the ice. A

good rule of thumb seems to be 1

cubic foot of bunker volume for

each 10 cubic feet of room space,

although several ice-refrigerated

rooms are performing satisfactorily

with a somewhat lower proportion

of bunker capacity to room volume.

In cases where the rooms are used

primarily for precooling, and for

storage only at the end of the harvest season, at least enough ice

bunker capacity should be provided

so that 1 reicing each day would

maintain the refrigeration capacity

during the peak load period. Since

a much greater air volume is needed

during precooling than during storage, some method of reducing air

flow should be provided. This can

be accomplished most easily by the

use of two-speed fan motors.

As stated previously, sulfur dioxide is fairly soluble in water and

the surface of melting ice provides

a considerable quantity of water.

Therefore it is desirable, so that a

reasonably constant concentration

of gas can be maintained during

the fumigation period, for the air

to bypass the ice while the sulfur

dioxide is being circulated. A satisfactory method of accomplishing

this is illustrated in figure 17. The

floor grid through which air normally enters the bunker is closed

and a hinged panel in the bunker

duct is opened. With this arrangement air is pulled directly from the

room and discharged again at the

top of the bunker duct. Figure 18

shows the same bunker duct section

with the grid cover removed and

the duct baffle closed for normal air

circulation through the ice bunker.

20
Figure 17.—Section of ice bunker duct with air return grid covered and bypass panel open as used

for circulation of SO2 in tlie room.

Comparative cost figures between

ice-refrigerated and mechanicallyrefrigerated storages are not available, but it is apparent that the

original cost of a mechanically-refrigerated plant would be materially higher than that of an ice-refrigerated plant of the same capacity.

On the other hand the cost of operation, on a per-ton of refrigeration

basis, would certainly be higher for

the ice-refrigerated plant. Even

under volume usage, ice probably

cannot be purchased on a delivered

basis for less than $5.50 per ton,

whereas an efficient mechanical

plant should provide refrigeration

at $2 or less per ton. The decision

on whether to use ice or mechanical

refrigeration must be based on such

factors as annual period of operation, available capital, delivered

cost of ice, and need for the lower

temperatures obtainable with the

mechanical plant. The decision

must be made on an individual basis, according to prevailing circumstances and need.

21
J ^

'A

BX-7122

Figure 18.—Section of ice bunl<er duct with air return grid open and bypass panel closed for

normal air circulation through the ice bunker.

Factors Affecting Refrigeration Capacity Requirements

The refrigeration requirement of

any storage plant must be based on

peak refrigeration load. This peak

usually occurs when outside temperatures are relatively high and

warm fruit is being moved into the

plant for precooling and storage.

The refrigeration load during the

peak of the harvest season will, of

course, depend upon the amount of

fruit received each day, the temperature of the fruit at the time it

is placed under refrigeration, the

specific heat of the product and the

final temperature attained. Other

factors affecting the total heat load

include vital heat or heat of respiration, heat leakage through room

surfaces and open doors, and heat

produced by electric motors, lights,

meclianical handling equipment,

and workmen.

Field Heat

Field lieat, or sensible heat as it

is sometimes called, is the heat that

must be removed from the product

to cool it to a given storage temperature. Any measures that can

22
B

•••

Plate 1.—4^ Stases in the development of gray mold rot. B, Stages in the development of

Clodosporium rot. C, Alfernaria rot in Emperor grape.
0^Ä mM

Plate 2.—A, Sound (left) and freezing injury (right) to Emperor grapes. S, Sulfur dioxide

injury to Emperor grapes. C, Sulfur dioxide injury to Tokay grapes. 0, Ammonia injury

to Emperor grapes, f. Box bruising of Emperor grapes, f. Nest rot stage of gray mold rot.
be taken to avoid high fruit temperatures at delivery, such as harvesting early in the morning or

shading the fruit from the sun, will

naturally reduce the refrigeration

load. The amount of refrigeration

required to lower the temperature

of a known amount of fruit a given

number of degrees can be calculated according to the following

formula: R=TRXPxS in which

R is the B.t.u.^ to be removed, TR

is the temperature reduction required in degrees F., P equals the

gounds of fruit or containers, and

is the specific heat^ of the

commodity.

According to this formula, the refrigeration requirement for reducing the temperature of 1,000 standard display lugs of grapes by 40° F.

would be as follows :

Fruit

Boxes

40 (°TR)X28,000 (P fruit) X0.82 (S) =918,400 B.t.u.

40 (^TR)X 4,000 (P wood)X0.33 (S)= 52,800 B.t.u.

Total—971^200 B.t.u^

almost doubles for each 10° rise in

temperature between 32° and 80°.

During precooling, th^ rate of

heat evolution decreases as the temperature is lowered and, consequently, a median fruit temperature should be used to calculate the

refrigeration load from evolved

heat. For example, in calculating

the heat evolved by grapes during

cooling from 75° to 35° F., the rate

of heat evolution at 53° could be

used. For the Thompson Seedless

variety this figure is given as 1,690

B.t.u. per ton of fruit per 24 hours.

On this basis, 1,000 lugs (14 tons

of fruit) of this variety would produce 23,600 B.t.u. and would require about 165 pounds of ice, or its

equivalent in mechanical refrigeration, to remove the vital heat alone

during a 24-hour precooling period.

After the grapes are down to

storage temperature the vital heat

production is substantially lower

than during the cooling period.

Thompson Seedless grapes produce

only about 430 B.t.u. per ton per

Since 144 B.t.u. are required to

melt 1 pound of ice, the removal of

971,200 B.t.u. would require an

amount of refrigeration equivalent

to that provided by the meltage of

6,744 pounds of ice or by 3.37 tons

of refrigeration. If a reduction in

temperature of more or less than

40° is required to bring the fruit to

storage temperature, the heat load,

of course, will be correspondingly

greater or less than the figure

shown.

VîfaI Heat

Vital heat is that produced by

fruits and vegetables as a result of

the respiratory process. As mentioned previously, grapes have a

relatively low rate of respiration as

compared with other fresh fruits

and vegetables. However, a certain amount of heat is produced and

it must be considered in the calculation of total refrigeration requirements. Vital heat production by

several varieties of vinifera grapes

(as calculated from the average

rate of carbon dioxide evolution at

different holding temperatures) has

been published (7^). At temperatures from near 30° to about 100°

F., the rate at which this heat is

generated increases as the temperature of the fruit increases. In fact,

the vital heat produced by grapes

^British thermal unit, the amount of

heat required to raise the temperature of

1 pound of water 1° F.

^Calculated on the basis of moisture

content according to the formula S=

0.008 aH-0.2 in which S is specific heat,

and a is the percentage of water in the

product.

23
24 hours at 32° F., so the vital heat

evolved from 1,000 lugs of grapes

at this temperature would increase

the load by only about 42 pounds

of refrigeration per day.

Heat Leakage

A substantial part of the refrigeration load in a cold storage plant

is due to heat leakage through exterior walls, the roof, and the floor.

The rate of such heat leakage will

depend upon the type of insulation

used, the thickness of the insulation, the moisture content of the

insulation, and the temperature

differential existing between the

outside temperature and the temperature maintained in the storage

room. Shredded redwood bark is

commonly used as wall and roof

insulating material in California

cold storages. The heat conductivity of this insulation has been

given {If) as 0.26 B.t.u. per hour

per 1° F. of temperature difference

per square foot of surface of a

1-inch-thick material having a density of 5 pounds per cubic foot.

Corkboard has approximately the

same insulating value as redwood

bark, but such materials as planer

shavings and crushed pumice have

considerably less insulating value

per inch of thickness {5), A wall

of cinder concrete with a density of

97 pounds per cubic foot permits

the passage of approximately 19

times as much heat as redwood bark

of similar thickness.

A storage room 25 by 40 feet with

a 9-foot ceiling would have 1,170

square feet of wall surface and

1,000 square feet each of ceiling and

floor surface. If the walls and

ceiling of the room were insulated

with 8 inches of redwood bark and

the floor with 4 inches of corkboard

and if the temperature differential

averages were 40° F. on the walls,

50° on the roof and 30° on the

floor, approximate heat leakage

into the room could be calculated as

follows :

J^ ^i'PT^'?O'V inn/1 ^

1,170 (sq. ft.) X0.26 (B.t.u./hr.) X24 (hrs.) X40 (°TD) _

8 (in. of EW bark)

Roof

1,000 (sq. ft.) X0.26 (B.t.u./hr.) X24 (hrs.) X50 (°TD) _

8 (in. of RW bark)

Floor

1,000 (sq. ft.) X0.27 (B.t.u./hr.) X24 (hrs.) X30 (°TD)

4 (in. of cork)

B.tM.

36,504

39,000

= 48,600

Total heat leakage per day 124,104

Thus, under the conditions specified, the refrigeration requirement

for heat leakage through exterior

surfaces would be almost one-half

ton per day.

Air Infiltration

Storage room doors are open for

substantial periods each day for

placement of fruit in the rooms and

removal of fruit for shipment. The

air entering the room, during the

exchange which occurs as a result

of temperature differential, may

carry large quantities of heat along

with it, particularly if outside doors

are open. Hukill and Smith {SI)

state that 100,000 B.t.u. per hour

can enter a room through a 4- by

7-foot outside door when a temperature differential of 30° F. exists

between room air and outside air.

It is apparent that any means of reducing this air exchange, such as

using light-weight swinging doors

24
or automatic door-opening and closing devices, will result in a material

reduction of total heat load.

Other Heat Sources

Heat is produced by electric motors, electric lights, and the combustion-type motors used on some fruithandling equipment. All of these

sources add to the total heat load

in the cold storage plant. The

amount of heat evolved from an

electric motor can be estimated at

3,000 B.t.u. per hour for each horsepower. Each kilowatt of incandescent light adds about 3,500 B.t.u.

per hour. In addition to these mechanical sources of heat, the vital

heat produced by workmen accounts

for 1,000 B.t.u. per man-hour. A

calculation of these factors for a

40-carlot room with six 1-horsepower fan motors operating continuously, six 200-watt lights burning

8 hours each day, and 2 men working

in the room for 8 hours each day,

will show the heat load in the room

from these sources as follows :

Electric motors

6 (motors) X 3,000

(Bt.u./hr.) X

24 (hrs.)

Electric lights

1.2 (KW)X 3,500

(B.t.u./hr.) X

8 (hrs.)

Workmen

2 (men) X 1,000

(B.t.u./hr.) X

8 (hrs.)

B,tM.

=432,000

= 33,600

= 16,000

Total heat load 481, 600

Thus the heat produced from incidental sources in this 1 room would

require about 1% tons of refrigeration per day.

Disorders of Grapes in Storage

During storage grapes are subject

to a variety of disorders, some of

which result from conditions that

exist during storage, some from conditions that already existed when

the fruit was placed in storage, and

others that result from a combination of postharvest and preharvest

factors. Deterioration of fruit in

storage can be the result of attack

by decay-causing organisms, of

natural aging processes, or of chemical, physical, or mechanical injuries. A thorough understanding

of each of these factors is necessary

to determine the most effective way

of controlling them.

Decay

Gray Mold Rof

The fungus Botrytis cinérea pers.

ex Fr. (gray mold), is widespread

in nature and causes decay in many

kinds of fruit, vegetables, and ornamentals. Since this organism is

capable of growth at low temperatures, it is one of the principal

causes of spoilage in grapes held in

cold storage. Gray mold is particularly prevalent in varieties such as

Emperor, Ribier, or Flame Tokay

when they are harvested late in the

season after exposure to high moisture conditions.

Symptoms.—Several common

names are used to describe the

various stages of gray mold rot.

The early stage of the disease commonly is called "slip skin" since,

after infection, the tissue just

beneath the surface of the berry is

attacked first, loosening the skin

from the underlying flesh. A slight

pressure applied to the berry causes

the skin to break loose and separate

from the firmer underlying tissue,

hence the name, "slip skin." There

may be a slight browning of the

affected areas of the berry, but at

this stage, the decay is not readily

discernible by appearance alone

(plate 1, ^).

25
Later, the causal fungus grows

through the entire inner flesh of the

berry, resulting in a soft, watery

mass of decayed tissue enclosed in a

still, somewhat intact, but browned

skin. Under moist conditions the

fungus sporulates on the surface

of the berry, producing the typical

gray mold stage of the disease.

However, when grapes are fumigated in storage, surface growth

and spore formation are usually

prevented. Fumigation does not

prevent development of the fungus

within previously infected berries.

Diseased berries gradually lose

moisture, shrivel, become a darker

brown color, and form the mummy

stage of decay. In storage the fungus may spread by contact from a

diseased berry to adjoining berries,

in which case the "nest rot" stage

of the disease is formed. When

nest rot occurs there is usually a

rather well-developed growth of

grayish-white mycelium over the

surface of the affected berries (plate

Control measv/res.—There are

four primary measures that may be

employed to reduce postharvest

losses from gray mold rot. Each of

these is related to and serves to

supplement the others:

1. Grapes that are to be shipped

directly to market after harvest

should be rapidly cooled to at least

40° F. and those that are to be stored

before marketing should be rapidly

cooled to 31° to 32° F. Holding

grapes at low temperature slows

the development of gray mold, but

does not in itself provide complete

control.

2. Soon after harvest, and at

intervals during storage, Vinifera

grapes should be fumigated with

sulfur dioxide (see section on sulfur dioxide for details). American,

or eastern, varieties of grapes are

not fumigated because of their

susceptibility to injury.

3. Vineyard applications of fungicides to prevent field infections

have been effective in reducing

decay in storage {18, 20, 21, 22, 26,

J{J¡., 65, 66). One of the most effective materials tested for this purpose has been captan. This fungicide is usually applied as a dust in

a formulation containing 10 percent captan, 50 percent sulfur, and

40 percent inert carrier. Application is made atthe rate of 20 pounds

per acre with the duster directed

toward the clusters. For Emperor

grapes grown in California the first

application should be made about

the middle of July and should be

followed by additional dustings at

3- to 4-week intervals with the last

one applied not later than 2 weeks

before harvest. This is a rather

expensive treatment and, though it

has been effective in years in which

the fruit is exposed to high moisture

conditions, it is of no particular

benefit in dry years. The grower

must consider the economic aspects

of the control measure, therefore,

before deciding upon its use.

4. Selective marketing to minimize decay losses has been shown

to be effective (see separate section

on this subject for details). The

use of a decay forecast allows the

storage operator to market early

those lots of grapes in which a high

percentage of decay is indicated and

to retain in storage only those lots

likely to remain sound.

Certain cultural practices have

been found to affect the incidence of

gray mold rot. The control of insects in the vineyard, for example,

indirectly affects decay by reducing

wounds in the fruit {S9,75), Dense

foliage around the fruit and weeds

around the base of the vines tend to

slow the time required to dry the

grapes after exposure to rainfall

and thus favor the development of

decay {11, 63),

Additional references on gray

mold rot are : {19, Jfi, il, 58, 55, 56,

60,67,68,69).

26
Cladosporium Rot

Cladosporium rot, {Gladosporium herbarum Pers,)^ is an important cause of spoilage in grapes

held in cold storage, particularly in

the Emperor and Flame Tokay varieties. Like gray mold rot, the

causal fungus is capable of growth

at and even below storage

temperatures.

S y mpt oTTbs , — Cladosporium

causes a black, firm decay that is

usually localized on one side of the

berry. The decay is not definitely

sunken, but the grape is flat or

wrinkled on the affected side. The

decay is shallow and usually does

not extend to the seeds. The affected tissue is firmly attached to

the skin and can be easily removed

with it. In storage, signs of the

fungus are usually not present on

the surface of the affected berries

(Plate 1, B), but when the fruit is

removed from storage and placed

at room temperature, a sparse surface growth of gray-green fungus

may be produced {18). Cladosporium rot is easily distinguished

from gray mold rot by its black

color and the fact that it usually remains localized rather than affecting the entire berry.

Control measures.—Fumigation

of vinifera grapes with sulfur dioxide reduces postharvest infections of grapes by Cladosporium

and other fungi and reduces spread

of decay from affected to sound

berries in storage and transit (see

section on sulfur dioxide). Applications of fungicides in the vineyard have reduced the development

of Cladosporium rot in stored

grapes but the disease is usually not

serious enough to warrant the expense of applying fungicides in the

field {26). Additional references

on Cladosporium rot are: (7, 13,

17).

Alternaría Rot

During the storage of Emperor

and some other varieties of grapes,

decay caused by species of Alternaría and StemphyliuTïh may develop. Infections by these organisms seem to occur quite early in

the harvest season, even in the absence of rainfall {26, 27). The

causal fungi often gain entrance

into the berry through the capstem,

causing a localized tan to dark

brown decayed area in the berry

(plate 1, C^). Since the fibrous conductive tissue ("brush") that leads

into the berry from the capstem is

attacked, affected berries are easily

shaken from the cluster. Species of

Alternaría and Stemphylivmi may

occasionally be isolated from other

parts of the berry where they cause

symptoms quite similar to those

caused by Cladosporium, but which

are not as dark in color.

Other Types of Decay

Although table grapes are subject to many types of decay in the

field, only the above-mentioned organisms commonly cause decay at

low storage temperatures under

California conditions. Decay

caused in the field by organisms

that are active only at high temperatures is usually culled out at

harvest or during packing and,

consequently, is not a serious disorder in storage. For information

regarding these disorders refer to

U.S. Department of Agriculture

Miscellaneous Publication No. 340,

Market Diseases of Fruits and

Vegetables : Grapes and Other

Small Fruits {60).

Physiologic Aging

Unlike certain other fruits,

grapes do not ripen after harvest

or improve in flavor or texture during storage. Since there is no

starch reserve in the grape, there

is no increase in sugar content after harvest. Grapes, therefore, are

at prime quality at harvest, and

subsequently suffer a gradual decline in quality.

27
As grapes approach the end of

their storage life the berries become

somewhat dull in color, losing the

brightness they had at harvest. Red

varieties assume a gray-purple color and green varieties turn a graygreen to brown color. The texture

becomes soft and flaccid and the

flavor resembles that found in

raisins.

Though picked from the vine, the

grape is still a living organism in

which a considerable amount of

sugar (carbohydrate) is stored.

The vital processes (respiration)

that go on in the fruit after harvest gradually use up the stored

carbohydrates, taking up oxygen

and releasing carbon dioxide, water, and a certain amount of heat

in the process (see section on vital

heat). The evolution of heat, which

is a measure of respiratory activity,

is lower in vinifera grapes at 32°

F. than in any other fruit except

the Winesap apple (79). Factors

that affect the rate of respiration

and consequently the aging of

grapes in storage are temperature,

fruit maturity at harvest, variety,

and sulfur dioxide fumigation.

Temperature.—Temperature is

the most important factor affecting the rate of respiration. Within

certain limits, the respiration rate

decreases with a lowering of the

temperature. De Villiers {IJi)

demonstrated that the respiration

rate in Red Muscat grapes was

about 2% times as great at 50° as

at 32° F., 7 times as great at 68°

as at 32° F., and 18 times as great

at 86° as at 32° F. The importance

of rapid cooling in relation to the

storage life of the fruit is apparent

from these results.

Maturity.—Immature grapes

have a higher rate of respiration

than mature ones. De Villiers found

that in Mataro grapes the respiration rate was about 1% times as

great in green as in firm ripe fruit.

Differences in respiration rates due

to maturity were greatest immediately after harvest and became less

pronounced toward the end of the

holding period. Grapes to be stored

for long periods, therefore, should

be of prime maturity, but not overripe. Since over-ripe fruit is more

susceptible to infection by the gray

mold fungus than less mature fruit,

this factor should also be considered when selecting fruit for longterm storage. Fruit having green,

immature stems appears to age

more rapidly in storage than fruit

with strong, amber-colored, mature

stems.

Variety.—The rate of respiration

differs considerably among different varieties of grapes. In general,

poor keeping varieties have a

higher rate of respiration than varieties that keep well in storage

{H). Thompson Seedless grapes,

for example, which have la maximum storage life of about 100 days,

respire more rapidly and evolve

more heat at 32° F. than Emperor

or Almería, both of which can be

successfully stored for periods as

long as 6 or 7 months. The normal storage life of several grape varieties is shown below. Certain lots

of each of these varieties may kee^)

for longer or shorter periods, depending upon the quality at

harvest.*

Variety : Months in storage

Muscat (Alexandria) 1 to li/4

Flame Tokay li/^ to 2i/4

Thompson Seedless (Sultanina) 2 to 3

Red Malaga (Castiza) 2 to 3

Malaga (V^hite Malaga)—. 2 to 3

Almería (Ohanez) 3 to 5

Ribier (Alphonse

Lavallee) 3 to 5

Emperor 4 to 6

Sulfur dioxide fumigation.—S^Yeral workers have found evidence

that fumigation with sulfur dioxide slows the rate of respiration

and thereby contributes to a lengthening of the storage life of the

fruit by physiologic means as well

as through decay control (see section on fumigation with sulfur

dioxide).

28
Chemical Injury

The principal chemicals to which

grapes may be exposed in storage

are sulfur dioxide and ammonia

gas.

For information concerning injury with sulfur dioxide, see section on fumigation with this chemical and plate 2, B^ G,

In plants using a direct expansion refrigeration system, grapes

are sometimes exposed to ammonia

gas that has escaped into the atmosphere of the storage room.

Eed-colored grapes turn blue and

green-colored fruit assumes a

slightly bluish cast in the presence

of ammonia (plate 2, D). The

change in color is caused by the reaction of ammonia with the sap in

the cells near the surface of the

fruit. When exposed to the gas the

sap becomes less acid and the acidsensitive pigments (anthocyanins)

in these cells change color.

Most of the gas enters the berries

around the capstem attachment,

and the adjacent tissues develop the

greatest discoloration. Similar discolored areas may form around

wounds in the skin. When exposed to ammonia the capstems

turn dark blue or black and portions of the stems become blue {16).

When an ammonia leak is detected, the gas should be cleared

from the room as soon as possible

because slight discolorations from

the gas disappear when the fruit is

removed from the ammonia atmosphere. The fruit will not recover from severe injury resulting

from long exposures to the gas.

The best way to remove ammonia

from the room is with water. In

rooms equipped with a spray system for clearing the room of sulfur

dioxide this can easily be done.

Another way of minimizing

damage from ammonia is to neutralize it with sulfur dioxide. Sulfur

dioxide reacts with ammonia to

form ammonium bisulfite, a whitish

crystalline substance. Approximately 4 pounds of sulfur dioxide

are required to neutralize 1 pound

of ammonia. No more than a 1

percent concentration of sulfur

dioxide should be used, as higher

concentrations might cause injury

to the fruit. If commodities other

than grapes are stored in the room,

sulfur dioxide cannot be applied.

Freezing Injury

Vinifera grape varieties when

injured by freezing have a dull

appearance and are soft and flabby.

After severe freezings they turn

brown and become wet and sticky

(plate 2, A). The berries of most

varieties will not freeze at temperatures as low as 28° F. because of

the high sugar content. However,

the stems and capstems are often

injured by temperatures that apparently have no effect on the berries.

The frozen stems are at first limp

and pliable, with a water-soaked

or dark-green appearance ; but they

soon dry, become dark colored, and

are more susceptible to mold invasion than sound stems. However,

if grapes are frozen after having

been fumigated with sulfur dioxide

in storage, the stems may not turn

dark, but retain their former green

or straw-yellow color. When berries, injured by freezing, are pulled

off the capstem, the brush (the small

bundle of fibres that extends from

the capstem into the berry) is

usually found to be shorter than

normal and somewhat browned

(60,79),

Desiccation

Desiccation in storage is evidenced by dry stems, shriveling of

the berries near the capstems, and

by loss of weight. There are several

factors that affect desiccation in

storage grapes :

Temperature.—H i g h temperatures in the field at harvest and ex29
posure to high temperatures after

harvest result in a rapid drying of

the stems and shriveling of the berries. Stems dry and turn brown

almost four times as fast at 100°

as at 70° F. and the berries lose

weight six times as fast at 100° as

at 70° F. {4-2), The importance of

careful handling to prevent exposure to high temperature is obvious.

There is evidence that picking

grapes in the cool part of the day

lessens drying of the stems {23^ 8^

9). Fruit should not stand in the

field or in the sun for long periods

and should be precooled to storage

temperatures as rapidly as possible.

The longer it takes to bring the

temperature of the fruit down to

the air temperature of the precooling or storage room, the greater the

loss of moisture from the fruit (see

section on precooling).

Humidity studies in South Africa

have shown that picking fruit during periods of high humidity lessens drying of the stems (23), It

should be pointed out, however, that

such conditions also favor the development of gray mold rot. The

maintenance of relative humidity

at approximately 90 percent in

storage will aid in preventing excessive drying of the stems (see section on relative humidity). The

relative humidity of the air surrounding the fruit within the package is affected by air movement

around the package in the storage

room. Once the fruit is cooled, it is

desirable to provide only enough air

movement to maintain the 81° F.

temperature of the fruit. In rooms

where favorable levels of relative

humidity or air velocity cannot be

maintained, curtains and package

liners of various types may be helpful in preventing desiccation.

However, these are a disadvantage

during precooling.

Maturity,—In California storage

varieties, such as Emperor, there is

less desiccation in mature than in

immature fruit. As the fruit matures the skin becomes more lignified and more resistant to water loss

{Ik)' Many growers do not harvest the Emperor until the stems

have developed a woody texture and

have begun to turn yellow or amber. When the vines are overcropped the stems remain green and

weak, the fruit fails to mature properly or there is a delay in reaching

maturity. Cultural practices that

favor early maturity of the grapes,

therefore, provide fruit that is less

susceptible to desiccation and less

likely to be exposed to conditions

favoring gray mold rot.

Mechanical Injury

Shatter

One of the most common forms

of mechanical injury in California

table grapes is shatter (the separation of the berries from the cluster). Varieties differ greatly in

their susceptibility to this disorder.

The Flame Tokay and Thompson

Seedless (Sultanina) varieties are

especially subject to shatter while

the Emperor and Ribier are relatively resistant. In most vinifera

varieties shatter results from, a pulling of the "brush" from the flesh of

the berry while in certain labrusca

types an abscission layer develops at

the junction of the capstem (pedicel) and the berry (^7). This latter type of shatter is also characteristic of certain vinifera varieties

grown in South Africa (^, 9).

Rough handling during picking,

packing, and transit is responsible

for a large part of the shatter that

occurs in storage grapes. W. T.

Pentzer of the U.S. Department of

Agriculture (unpublished data)

found that shatter caused by transit

impacts could be materially reduced

by eliminating all slack from the

load in the refrigerator car. This

was done by compressing the load

with a mechanical "car-squeeze"

and bracing the center space so that

30
load tightness is retained during

transit. Cultural practices such as

thinning help to strengthen the

stems and reduce shatter. There is

also evidence that hot, dry weather

and a deficiency of soil moisture

during the period of ripening contribute to shatter (5, 9). Girdling

Thompson Seedless vines to increase the size of the berries also

strengthens the attachment of the

berries to the stems, thereby reducing shatter {33), Pentzer (^7)

found that naphthalene acetic acid

(NAA) did not affect the adherence

of the berries in vinifera grapes, although this material was found to

reduce drop in other fruits. He attributed the ineffectiveness of NAA

applications to vinifera grapes to

the lack of a definite abscission

layer. Grapes that firmly adhere to

the stems at harvest sometimes develop shatter after prolonged

storage. If grapes are allowed to

become over-mature before harvesting, more shatter occurs than when

the fruit is harvested at prime maturity {H)^

Postharvest conditions that

favor desiccation also favor shatter.

Shatter is reduced by rapidly cooling the fruit as soon after harvest

as possible.

Bruising

Bruising commonly occurs in

berries that are in contact with the

sides or bottom of the packed container (plate 2, E), Affected berries are somewhat flattened, show a

brown discoloration, and are situated on one side of the bunch.

When grapes are fumigated in

storage or transit, the bruised areas

may become bleached as sulfur

dioxide penetrates the berry readily

at points where the skin is weakened. The small, dried undeveloped "shot berries" that drop off the

cluster and collect in the bottom of

the box sometimes puncture or

bruise the skin. Severe bruising

may predispose the fruit to infection by decay organisms.

Protective liners to prevent the

fruit from touching the wooden

sides of the box and adequate

padding in the bottom of the box

help to reduce bruising.

Berry Cracking

As the temperature of fruits is

lowered, the turgidity generally increases. Varieties in which the berries have thin skins, such as

Thompson Seedless, will sometimes crack during precooling or in

the early stages of cold storage.

Cracks in the skin can frequently

be found in the Flame Tokay at

harvest and may be infected with

the Cladosporium fungus. These

cracks are crescent-shaped, usually

occur at the blossom end of the berry, and are rarely over one-fourth

inch long and one-eighth inch deep.

The disorder apparently occurs

more extensively in grapes that are

very turgid at harvest as a result of

exposure to wet weather or other

high moisture conditions. No effective control measures have been

developed for cracking. Fortunately it affects a relatively small

proportion of the crop.

Fumigation With Sulfur Dioxide

The effectiveness of sulfur dioxide in retarding the activity of

spoilage organisms in fresh grapes

was demonstrated in 1925 by Winkler and Jacob (77). Shortly thereafter, methods of applying the gas

to commercial shipments of grapes

were developed {32) and the various

factors related to decay control and

fumigation injury were determined

{6,30, 32, 48\ Jß, 77).

Sulfur dioxide is used primarily

to control grey mold rot in storage.

Grey mold {Botrytis cinérea) is

31
one of the few organisms causing

grape decay that is capable of

growth at the low temperatures at

which grapes are stored. If the

berries are infected with this organism before storage, fumigation with

sulfur dioxide is ineffective in killing such infections and the decay

continues to develop. How^ever, the

gas kills fungus spores present on

the surface of the fruit and consequently prevents post-harvest infections. When properly applied it

also prevents the spread of decay

by contact from previously infected

berries to sound ones, thus eliminating "nest-rot."

Decay caused by the other low

temperature organisms, Cladosporimn herhariÁin and species of

Alternaría^ is also reduced by sulfur dioxide fumigation. As in grey

mold, fumigation kills spores on the

surface, but does not control infections that have occurred before

storage (^7).

In addition to reducing decay,

sulfur dioxide is effective in setting

the light green or straw yellow

color of the stems. Without fumigation grape stems turn a dark

brown or black color in storage.

Fumigation also tends to prevent

the berries from becoming separated from the cluster ("shattering") (.54, 35, 68), Wounds that

would otherwise act as entrance

ports for decay organisms are

cauterized by the fumigation.

Grapes treated with sulfur dioxide have a slower rate of respiration

than untreated ones {62, 77) and

this lowered rate of respiration

tends to lengthen the storage life of

the fruit. Pentzer et al {62) found

that when Emperor grape tissue

contained 87 p.p.m. sulfur dioxide,

respiration was reduced to 8 percent

of normal at 32° F. However, at

this concentration the gas caused

serious injury to the fruit. At a

concentration of 22 p.p.m. no injury

occurred and the respiration rate

was reduced to 82 percent of that in

an untreated check lot. Although

the effect of sulfur dioxide on the

respiration rate is slight at the concentrations employed commercially,

there is a small reduction in the loss

of stored carbohydrates from the

fruit. The sensitivity of the relationship between the respiration

rate and the concentration, of sulfur

dioxide in the tissues is demons

strated by the fact that the respiration rate increases during the

intervals between fumigations in

storage {87).

Methods of Applying Sulfur

Dioxide

Sulfur dioxide may be applied

either by releasing the compressed

gas from steel cylinders, or by adding potassium or sodium bisulfite to

the package. At one time the gas

was generated by burning sulfur in

the fumigation chamber, but this

method is no longer in common

usage.

Fumigation With the Liquified Gas

Fumigation may be accomplished

in special fumigation rooms, in

precooling rooms, in refrigerated

storage rooms, or in railway refrigerator cars. Initially a 1 percent

concentration of gas is applied to

the fruit for 20 minutes. This is

often done in a special gassing

room at prevailing outside air temperatures. During cold storage the

fruit is furnigated at weekly or 10-

day intervals with ^ percent concentrations of sulfur dioxide for 20

minutes {29, 61),

The concentration of gas can be

calculated on the basis of free air

space in the chamber used for the

fumigation {2). First, determine

the volume of the chamber in cubic

feet ; next subtract 0.5 cubic foot for

each lug of grapes to be fumigated.

The fruit in each lug occupies ap32
proximately 0.5 cubic foot of space,

when air voids between the berries

are taken into account. Since 1

pound of sulfur dioxide is equivalent to 5.5 cubic feet of gas at 32°

F., the free space (cubic feet) in the

chamber multiplied by the percent

concentration desired, divided by

5.5 will give the pounds of gas

needed. For example, the amount

of sulfur dioxide required to make

a 0.25 percent concentration of the

gas in a 3,200 cubic foot storage

room containing 500 lugs of grapes

is calculated as follows :

[3,200- (500X 0.5) ] X 0.0025

_____ . _-_ "

-1.34 lbs.

Cylinders containing the correct

weight of gas for specific storage

rooms or other fumigation chambers are provided by various service

companies to the storage operator.

The cylinder is connected to a pipe

leading into the fumigation chamber, the valve is opened and the cylinder is heated in a water bath to

drive all the gas into the chamber.

The sulfur dioxide is rapidly mixed

with the atmosphere inside the

chamber by fans or blowers to insure uniform distribution of the

fumigant.

After a 20-minute exposure of the

fruit to the fumigant, the sulfur dioxide is removed either by opening

room doors, by ceiling exhaust fans

or by a water spray system (see section on refrigeration systems).

Sulfur dioxide is usually cleared

from fumigated refrigerator cars

by circulating the air through the

ice bunkers. The gas is dissolved

in the film of water on the melting

ice surfaces.

For fumigating grapes in a refrigerator car a fan with canvas

baffles should be used in the brace

to distribute the sulfur dioxide uniformly in the load. Without a brace

fan, injurious concentrations of gas

accumulate in the space above the

load and in the open brace, and relatively little fumigant reaches the

fruit within the load, providing

poor control of decay (72),

A method sometimes used to estimate the amount of gas needed for

a 0.25 percent concentration is to

use % to 1 pound of gas for each

1,000 lugs of grapes. Until the

room is half filled with grapes an

additional % pound of sulfur dioxide is used for each carload unit of

empty space. Thereafter, no gas is

added for the unoccupied space

Under experimental conditions it

has been found that continuous exposures to very low concentrations

of sulfur dioxide (30 p.p.m.) were

effective in controlling decay and

resulted in less injury to certain

grape varieties than did short exposures of higher concentrations of

gas (35, 87, 68). To utilize this

method of fumigation a device to

automatically control the concentration of sulfur dioxide in the storage room was developed in South

Africa. Although this method of

fumigating grapes may be adaptable to certain types of small storages, the maintenance of a constant

concentration of sulfur dioxide in

large storage rooms would be difficult as it would preclude normal

handling operations to remove fruit

at intervals for marketing. In

rooms using ice as a refrigerant, low

concentrations of sulfur dioxide

could not be maintained as the gas

would be absorbed by the ice. The

same difficulty would be encountered in rooms refrigerated by a

brine-spray system.

Fumigation With Bisulfite

Sodium or potassium bisulfite is

utilized as a source of sulfur dioxide under conditions that preclude

fumigation of grapes in the storage

33
room or refrigerator car. Such conditions exist in fruit that is exported in the sawdust pack and

which cannot be "room fumigated"

during transit aboard ship. Prior

to shipment, grapes destined for export are usually fumigated in the

usual way at intervals during storage and the sawdust and bisulfite

are not added until the grapes are

ready to be shipped. The sawdust

acts as a dispersing agent for the

bisulfite as well as a cushion for the

fruit against mechanical injury.

Sodium bisulfite can also be used

in the standard display lug by distributing the powder evenly in the

excelsior pad placed in the bottom

of the box. The pad is slit to add

the bisulfite and the paper cover is

then replaced so that the fruit is

not in direct contact with the powder. Not over 5 grams of bisulfite

should be used in either the standard 28-pound display lug or in the

sawdust pack as larger amounts

may cause injury to the fruit {6^ 45^

Sulfur dioxide is produced as a

result of the reaction of bisulfite

with moisture in the atmosphere.

If there is not too much moisture

in the package, the release of gas is

quite slow and the fruit, therefore,

is exposed to low concentrations of

sulfur dioxide over a long period

of time. Care must be taken, however, never to use bisulfite under

abnormally high moisture conditions as this w^ould result in such

a rapid release of gas that chemical injury to the fruit would occur.

Such high moisture conditions

would exist, for example, if wet

sawdust were used or if wet fruit

were packed.

The rate at which bisulfite releases sulfur dioxide gas can be

regulated to a degree by mixing it

with various hygroscopic materials,

such as dehydrated alum or silica

gel {38, ¿7, 69, 71, 73), Such materials reduce the amount of moisture available for reaction wdth the

bisulfite and consequently slow the

release of gas. However, these

methods have only been used under

experimental conditions and have

not gained wide commercial application in the United States.

Symptoms of Suifur Dioxide

Injury

One of the most common types of

injury that may occur in grapes

fumigated with sulfur dioxide gas

is a bleaching or discoloration of the

fruit. This is most pronounced at

breaks in the skin or at the attachment of the capstem to the berry.

Although the gas can enter the

berry through the vascular tissue

of the capstem, it penetrates more

readily through tears that occur in

the skin near the capstem attachment during handling. As a result,

the tissue underlying such wounds

tends to dry out and collapse, forming a pit or depression that is a

well-known symptom of sulfur

dioxide injury. This type of injury

is particularly prevalent in the

Emperor variety when stored for

long periods (plate 2, ^).

In certain varieties, such as Flame

Tokay, injury may occur as small,

bleached, and slightly sunken pits

scattered over the entire surface of

the berry (plate 2, 6^). These detract from the normal bright color

of the fruit and can make the fruit

unmarketable.

When sulfur dioxide injury

occurs in red varieties, the color of

affected areas of the berries may

change to pink or white ; with blue

or black varieties, the color becomes

a lighter blue or pink; and with

white varieties, affected areas sometimes assume a greyish cast. Injury is more apparent after the

grapes have been exposed to warm

temperatures for several hours than

34
it is immediately after the fruit is

removed from cold storage. Injured berries may turn brown at

warm temperatures due to oxidation reactions in the affected tissues.

Immediately after fumigation,

grapes may have a slightly sulfurons taste and badly injured fruit

may have a distinctly disagreeable,

astringent flavor. However, it has

been found that 50 percent of the

sulfur dioxide residue in the fruit

disappears within 2 days after

treatment and the fruit is almost

entirely free of sulfur dioxide within 5 days after treatment {4-8).

Consequently, fruit treated Avlien

shipped from California is almost

entirely free from sulfur dioxide by

the time it reaches eastern markets.

Factors Affecting Sulfur Dioxide

Injury

The amount of sulfur dioxide injury that develops in fumigated

grapes is directly related to the

amount of the fumigant absorbed

by the fruit. Absorption of sulfur

dioxide is de|)endent upon the particular variety, the maturity of the

fruit, the fruit temperature, the

|)resence of wounds and the concentration, frequency, aud lengtli

of exposure to tlie gas.

Variety

Certain varieties of table grapes

such as Malaga, Thompson Seedless (Sultanina), and Castiza (Eed

Malaga) absorb sulfur dioxide

more rapidly than Eibier (Alphonse Lavallee) and Alicante

Buschet. The rate of SO2 absorption by the Emperor variety is

slightly greater than that of Eibier,

but considerably lower than that of

Thompson Seedless {JfS^ 51 ).

Flame Tokay is quite susceptible to

injury as evidenced by the pitting

that frequently is found over the

surface of this variety after fumigation {64). Many of the varieties of

grapes grown in South Africa are

particularly subject to injury from

sulfur dioxide. Consequently,

when the fumigant is employed, it

is administered in much lower concentrations than are used commonly

under commercial conditions in the

United States {18,58).

Maturity

Immature fruit absorbs gas more

rapidly than mature fruit (^).

Winkler and Jacob {32, 77) found

that ripe Muscat grapes (27° Balling) absorbed about one-half as

much sulfur dioxide as green ones

(18° Balling) and about one-sixtli

as much as very green ones (13°

Balling). Since very mature

grapes are more subject to infection

by decay organisms and absorb

sulfur dioxide less readily than immature grapes, it may sometimes be

desirable to fumigate them with

slightly higher concentrations of

gas than are ordinarily used.

Fruit Temperature

Warm grapes absorb more sulfur

dioxide than cold grapes {82, 48,

77), Pentzer and Asbury {^8)

found that Thompson Seedless

grapes absorbed more than twice

as much gas at 72° than at 89° F.

Malaga grapes absorbed almost

three times as much gas at 75° than

at 48° F. Temperature is a particularly important factor in sulfur

dioxide injury when varieties that

absorb sulfur dioxide rapidly are

being fumigated {58).

Wounding

The intact skin of most varieties

of vinifera table grapes grown

commercially in California possesses a high degree of resistance to

penetration by sulfur dioxide gas.

However, the gas is able to penetrate the berry through the vascular tissue of the capstem and readily

35
penetrates through any type of perforation of the skin caused by

physical wounding, the activity of

decay-causing organisms, or other

weakening factors. These characteristics are desirable to a certain

degree since the fumigant tends to

concentrate in the tissue at points

that are most susceptible to invasion by spoilage organisms. The

fact that grapes are to be furriigated, however, is no excuse for

rough or careless handling, as the

bleaclied, pitted areas that form at

points of wounding lower the quality of the fruit {32,77),

Concentration and Length of Exposure to Fumigant

The higher the concentration

and the longer the exposure, the

more sulfur dioxide grapes absorb.

Of all the factors considered, these

are the most important in relation

to fumigation injury. The use of

circulating fans or blowers is essential to distribute the gas uniformly in the fumigation chamber

and to prevent injurious concentrations from building up near the

gas inlet. It is also important that

an efficient method of exhausting

the room of fumigant is used to prevent over-exposure to the gas.

When refrigerator cars are fumigated, allowance must be made for

the ice in the bunkers since sulfur

dioxide is rapidly absorbed by the

melting ice.

To determine the concentration

and length of exposure that will

control spoilage organisms without

injury to the fruit, all the above

factors as well as those related to

infection by decay organisms must

be considered. The concentrations

and exposures cited under "Methods of Applying Sulfur Dioxide"

meet the needs for fumigation

under average conditions. Commercial operators sometimes vary

the concentration and exposure to

meet the needs of specific situations.

Obviously, since a given storage

room may contain grapes of several

varieties, maturities, and with different decay potentials, one treatment cannot fit the optimum requirements for each factor. To cite

an extreme example, the fumigation

requirements of an immature,

warm, injury-susceptible variety,

not exposed to conditions favoring

infection would be quite different

from those of a mature, cooled, injury-resistant variety that had been

exposed to rainfall.

Workers in South Africa have

found that certain of their varieties

can absorb about 20 p.p.m. SO^

without injury. This concentration of sulfur dioxide in the tissue

was obtained if the grapes were

fumigated with 0.25 to 0.3 percent

of the gas for 20 minutes (58),

Consequently, the 1 percent concentration of SO2 commonly used

for the initial fumigation of grapes

in the United States would not at

all be suitable for fumigation of

these South African varieties.

Frequency of Fumigation During

Storage

Another factor affecting the

amount of sulfur dioxide absorbed

by grapes is the frequency at which

fumigations are made during the

storage period. The common commercial practice is to fumigate at

7- or 10-day intervals with a 0.25

percent concentration of gas for 20

minutes. Under laboratory conditions grapes were fimiigated at intervals of 7, 14, or 21 days to determine the effect of frequency of

SO2 fumigation on injury and decay development. No consistent

relation between frequency of fumigation and injury could be demonstrated in these studies. There was

some evidence that mechanical injuries, which allowed the gas to

penetrate the berries more readily.

36
and the high initial concentration

of gas (1 percent) were more important as causes of injury than

was frequency of fumigation during storage. When grapes were

stored for long periods (5 months),

more decay developed in those that

received the less frequent fumigations than in those that were fumigated more often. The frequencies

of fumigation used in this study

had no significant effect on decay

in grapes stored for short periods

(3 months) (29),

Precautions To Follow When

Using Sulfur Dioxide

Human Toxicity

The pungent odor of sulfur dioxide is easily recognized and can be

detected in concentrations as low as

30 to 40 parts per million (p.p.m.).

At 400 p.p.m. the gas becomes extremely irritating and can cause injury to the mucous membranes of

the eyes, nose, and mouth. At 2,500

p.p.m. (0.25 percent, the concentration commonly used to fumigate

grapes in storage), the gas can

cause respiratory spasms and deatli

if the victim cannot escape from the

fumes (S).

If exposed to irritating concentrations of the gas, affected areas

should be fluslied with large quantities of water. A few drops of dilute ephedrinal sulfate will give relief when applied to the nose.

Goggles and a gas mask eff'ective

against acid type gases should be

worn in the presence of even weak

concentrations of the gas.

Injury to Other Commodities

Grapes are almost unique in their

ability to withstand sulfur dioxide

fumigation. Concentrations of the

gas commonly applied to grapes

cause severe injury to almost all

other fresh fruits and vegetables.

For this reason grapes must not be

stored in the same room with other

produce and during fumigation the

gas must not be allowed to move

through leaks in walls, or through

hallways or ductwork into adjoining rooms where other commodities

are stored. If grapes are shipped

in mixed loads with other fruit in a

refrigerator car, the car must not

be fumigated. Severe injury to

peaches, nectarines, plums, and

other commodities has been observed when these fruits have been

shipped with grapes in fumigated

cars.

Corrosive Effect on Equipment

Sulfur dioxide forms sulfurons

acid when dissolved in water.

Metal surfaces upon which moisture

collects in cold storaqfe rooms therefore become covered with sulfurons

acid during and after fumigation.

The acid is extremely corrosive to

both iron and zinc, causing the deterioration of coils, brine-spray

chambers, and other equipment

made of these metals. Some protection is afforded by treating exposed

metals with acid resistant paints.

A minimum of electrical wiring

sliould be used inside grape storage

rooms and switches and other control equipment should be located

outside the room if possible.

Other Precautions

Certain precautions already

noted under "Factors affecting sulfur dioxide injury" should be

stressed. When bisulfite is being

used as a fumigant no more than 5

grams per lug or chest should be

applied. It should be evenly dispersed in the package and not in

contact with the fruit and it should

not be used with wet grapes or wet

sawdust. Grapes treated with bisulfite should not be refumigated

with sulfur dioxide in storage because bleaching may result from the

combined treatment (45)»

37
asao

LOOS

RAIN 1.61 IN.

6 10 14 18 22 26 30^^3 7 M IS 19 23 27

. OCT. NOV.

A HARVEST DATE

BN 7115

2.5

2.0-

^1.5

<

^1.0

RAIN 0.18 IN. 1.35 IN.

1 /

FORECAST

V/ .

I 5 9 ^"^7 21 25 29 ,2 6 10 14 18 22

^ OCT. NOV.

B HARVEST DATE

HN-711t;

Figure 19.-—Interrelation of decay forecast and decay actually developing in stored Emperor

grapes. A, Fresno vineyard, 1952. B, Fresno vineyard, 1953.

Selective Marketing of Storage Lots

Since decay and other disorders

vary considerably from one lot of

stored grapes to another, it is desirable to arrange and identify the

lots in storage in a way that will

enable the shipper to market poor

keeping lots early and retain only

sound, high-quality fruit for late

marketing. To determine the keeping quality of different lots of

grapes, the shipper may rely on his

knowledge of the storage history

of fruit harvested in past years

from various vineyards, on the general appearance of the fruit at

harvest, on the weather to which

the fruit had been exposed before

harvest, on periodic inspections

made during the storage period, or

on a laboratory forecast of the potential storage decay present in specific lots of fruit at harvest. A

rating of lots based on all but the

last two of these factors requires

a considerable amount of experience and reliable storage records

over a period of years. Such may

not be available in a new storage

plant, in one in which the personnel are new, or in one storing fruit

that may come from a different

source each year. Neither can fac38
tors related to the effect of exposure to weather before harvest always be accurately evaluated.

Inspection and forecasting, therefore, offer a more precise way of

measuring and estimating storage

disorders.

Inspection in Storage

Stowage of grapes in storage

should allow ready access to each

lot and inspections of randomly selected boxes from each lot should

be made at regular intervals. Lots

in which decay begins to appear

are marketed immediately but if

too much decay is present, the fruit

may have to be trimmed and repacked. If a lot is not inspected

frequently enough, decay may develop to the point where the whole

k)t becomes unsalvageable. The

fi'equency at which grapes are inspected in storage varies with the

time of year and the opinion of the

storage operator about tlie keeping

quality of the particular lot. If a

lot was suspected of being particularly subject to decay, it would

probably be inspected at weekly intervals or before each fumigation.

Fruit thought to be sound would be

inspected less frequently. At the

beginning of the storage period inspections are usually less frequent

than they are toAvard the end of

storage.

Forecasting Decay in Storage

Grapes

Most of the decay that develops

during storage in the Emperor and

other late-harvested storage varieties is caused by the gray mold

fungus, Botrytis cinérea. A

method of measuring the potential

amount of decay in storage caused

by this organism has been developed and found to be exceptionally

accurate under laboratory conditions. The method has also been

adapted to several commercial storage operations and has been used

as a guide to marketing individual

lots of storage grapes {28).

The forecast is based on the

premise that (1) decay in stored

grapes is caused primarily by infections that occur in the vineyard

before harvest, but which have not

dev^eloped far enough to be detected and removed during packing, and (2) that fumigation kills

only fungus spoi'es on the surface

of the berries and not the fungi

that have entered the berries before

harvest. ^ These fungi continue to

grow within individual berries

during storage despite fumigation.

The fumigation does, however, reduce the occurrence of new infections due to spread of decay from

diseased to sound berries.

Method

Applying these principles to

measuring infections present in

grapes at harvest, the amount of

decay that will develop in storage

can be predicted. It is important,

however, that only field infections

be measured and not infections that

might occur after harvest, which

are largely controlled by sulfur

dioxide fumigation.

The forecast is made by taking a

sample of individual berries from

each lot of grapes to be tested. The

sample is placed in glass jars and is

fumigated with sulfur dioxide to

kill all surface contamination. After fumigation, the jars are covered

and the fruit is held under sterile

conditions at high humidity and at

room temperature. Under these

conditions, decay develops within

10 days that would require several

months to develop in cold storage.

By calculating the percentage decay occuring in the test sample, the

amount of decay that will develop

during storage in corresponding

lots can be predicted.

39
Unless the sample is representative, the forecast would provide an erroneous idea about

decay in the particular lot being

tested. Under experimental conditions samples are taken from

marked vines randomly situated in

each of the vineyards being tested.

Fruit from these vines is picked

at weekly intervals through the

normal harvest season and taken to

the laboratory. A portion of the

fruit from each lot is used for the

forecasting test and the remainder

is placed in cold storage for approximately 3 months. With this

method of sampling there is a

correlation between the percentage

decay that develops in the forecasting test and that which subsequently develops in correspondinglots in storage (Figure 19, Ä^ß)-

Under commercial conditions

samples can be taken by clipping individual berries from the packed

lugs of grapes as they pass along

the conveyor toward the lidding

machine. This method of sampling

provides a good measure of the potential decay present in specific lots

of grapes going into storage and

requires less time and labor than

collecting the samples in the vineyard. However, when grapes are

packed in the field, it may be more

practical to collect samples in the

vineyard as is done experimentally.

Effect of Harvest Date

Since field infections normally

increase as the season progresses,

the forecast indicates the harvest

date after which grapes should not

be held for long-term storage. In

years when heavy rains occur during the harvest, this date is fairly

obvious. However, in otlier years

when light rains, periods of high

humidity, or heavy morning dew or

fogs occur, their effect on infection

may not be recognized. The forecast measures infections due to all

these factors.

Effect of Source of Storage Lot

The amount of decay in storage

varies with lots harvested from different vineyards or districts. In

years when no rain occurs during

the harvest season, this factor may

be the principal source of variation

in decay between lots. However,

variation in decay between vineyards is also important in seasons

when the fruit is exposed to heavy

rains. Grapes in certain vineyards

are capable of withstanding adverse

weather conditions without severe

decay losses, while others suffer decay after exposure to only mildly

unfavorable weather conditions.

To detect these variations the forecasting test is particularly useful

(see section on decay for discussion

of the factors related to infection).

Application of Forecast

The forecasting test provides a

relatively precise method for the selective marketing of storage lots accordini^: to their decay potential. If

a high percentage of decay in a

given lot is indicated by the forecast, the shipper can market this lot

early, before decay has a chance to

develop. If the forecast indicates

that a particular lot is sound, that

lot can be held safely in storage to

take advantage of favorable markets late in the storage season

(27, £8).

40
LITERATURE CITED

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1949. TUNNEL METHOD OF PRECOOLiNG GRAPES. Blue Anchor 26(3) : 6-7,

21, 29, illus.

(2) ALLEN, F. W. and PENTZER, W. T.

1936. STUDIES ON THE EFFECT OF HUMIDITY IN THE COLD STORAGE OF FRUITS.

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(3) and PENTZER, W. T.

1955. (COLD STORAGE OF) APPLES, PEARS, AND GRAPES. REFRIGERATING DATA

BOOK. The American Society of Refrigerating Engineers, pp. 19-

01 to 19-16. New York.

(4) AMERICAN SOCIETY of HEATING and VENTILATING ENGINEERS.

1945. HEATING, VENTILATING, AIR CONDITIONING GUIDE. 808 pp., illus. New

York.

(5) AMERICAN SOCIETY OF REFRIGERATING ENGINEERS.

1942. REFRIGERATING DATA BOOK. Ed. 5, 515 pp., illus., New York.

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1936. FURTHER OBSERVATIONS ON MOLD CONTROL IN GRAPES DURING TRANSIT AND

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(7) BERRY, J. A. and MAGOON, C. A.

1934. GROWTH OF MICROORGANISMS AT AND BELOW o° c. Phytopathology 24 :

780-796.

(8) BEYERS, E.

1938. DROP BERRY AND DESICCATION OF STALKS IN WALTHAM CROSS GRAPES.

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Lab. Ann. Rpt. 1936-37 : 91-101. Capetown.

(Í))

1939. FURTHER INVESTIGATIONS OF FACTORS AFFECTING "DROP" AND DESICCATION

OF STALKS OF WALTHAM CROSS IN STORAGE. Uuion South Africa, Dcpt.

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(10) BLUMER, S.

1947. VERSUCHE ZUR BEKÄMPFUNG -DER GRAUFÄULE {l)otrytis Cinérea).

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(11)

1951. DIE BEKÄMPFUNG DER KRANKHEITEN UND SCHÄDLINGE IM REBBAU.

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(12) CARRICK, D. B.

1930. SOME COLD-STORAGE AND FREEZING STUDIES ON THE FRUIT OF THE VINIFERA

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(14) DE VILLIERS, F. J.

1926. PHYSIOLOGICAL STUDIES OF THE GRAPE. Uniou South Africa, Dept. Agr.

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1950. THE EFFECTS OF AIR BLAST PRECOOLING ON THE MOISTURE CONTENT OF THE

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(16)

1952. AMMONIA DAMAGE TO STORED FRUITS AND NUTS ; SULFUR DIOXIDE AS A

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1935. DEVELOPMENT DU CLADOSPORIUM HERBARIUM SUR DES RAISINS Â BASSE TEMPÉRATURE. Compt. rend. soc. biol., 118: 708-710, illus. Paris.

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(20)

1937. STUDIES ON THE PHYSIOLOGY AND PARASITISM OP BOTRYTIS CINÉREA

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41
(21)

1939. COMPARISON OF THE EFFECTIVENESS OF VARIOUS FUNGICIDES AND THE METHODS OF THEIR APPLICATION FOR THE CONTROL OF BOTRYTIS ROT OF GRAPES.

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1943. SWAWEL VIR DIE BESTRYDING VAN WINGERDSIEKTES ( SULFUR FOR THE CONTROL OF VINEYARD DISEASES). Farming in South Africa 43: 472-474,

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(27)

(28)

(29)

1955. A METHOD OF FORECASTING DECAY IN CALIFORNIA STORAGE GRAPES. Phytopathology 45 : 229-232.

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(30) ~— and PENTZER, W. T.

1953. THE VALUES OF FUMiGANTS. U.S. Dept. Agr. Yearbook of Agriculture,

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(31) HuKiLL, W. V. and SMITH, E.

1946. COLD STORAGE FOR APPLES AND PEARS. U.S. Dept. Agr. Circ. 740, 61 ])p.,

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(32) JACOB, H. E.

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(33)

1939. GIRDLING VINES FOR TABLE GRAPES. Blue Auchor. 16(6) : 6-7.

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1954. LONG-TERM STORAGE OF GRAPES. Farming in South Africa 29: 157-159.

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42
(42)

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1940. THE EFFECT OF SO2 GENERATING TABLETS. Uuiou South Africa, Dept. Agr.

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(59) and PIAGET, J. E. H.

1952. THE USE OF BISULPHITES IN THE CONTROL OF WASTAGIO IN FRESH GRAPES.

Farming in South Africa, 27 : 477-479.

(60) ROSE, D. H., BRATLEY, C. O., and PENTZER, W. T.

1939. MARKET DISEASES OF FRUITS AND VEGETABLES : GRAPES AND OTHER SMALL

FRUITS. U.S. Dept. Agr. Misc. Publ. 340, 27 pp., illus.

(61) and PENTZER, W. T.

1947. COMMERCIAL METHOD OF FUMIGATING GRAPES AVITH SULPHUR DIOXIDE.

Blue Anchor 24(4) : 6-7, 34.

(62) RYALL, A. L.

1952. A STUDY OF PACKAGING MATERIALS. Ice and Refrig. 123(2) : 11-15, illus.

43
(63) SCHELLENBERG, A.

1955. KULTITRMASSNAHMEN ZUR VERMINDERUNG DER TRAUBENFÄÜLNIS.

Schweiz. Z. Obst- u. Weinbau. 64: 107-112.

(64) SNYDER, E.

1937. GRAPE DEVELOPMENT AND IMPROVEMENT. 1937. U.S. Dept. Agv. Yearbook

of Agriculture, pp. 631-644, illus. Washington.

(65) STAEHELIN, M.

1946. STATION FEDERALE D'ESSAIS VITICOLES ET ARBORICOLES ET DE CHIMIE

AGRICOLE, À LAUSANNE ET 1 PULLY. Rapport d'actlvité 1945. Ann.

Agr. Suisse. 47(8) : 741-842.

(66) and WURGLER, W.

1947. STATIONS FEDERALES D'ESSAIS VITICOLES, ARBORICOLES ET DE CHIMIE

AGRICOLE, À LAUSANNE ET À PULLY. Rapport d'actlvité 1946. Ann.

Agr. Suisse. 48(8-9) : 701-792.

(67) STALDER, L.

1953. DAS PROBLEM DER BOTRYTISBEKÄMPFUNG IM WEINBAU. SchwelZ. Z.

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(68)

(69)

1953. WITTERUNG UND TRAUBENFÄULNIS. Schweiz. Z. Abst- u. Weiubau. 62:

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1953. UNTERSUCHUNGEN ÜBER DIE GRAUFÄULE {hotryUS Cinérea PERS.) AN

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(70) STUBENRAUCH, A. V. and MANN, C. W.

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1958. UNITED STATES DEPARTMENT OF AGRICULTURE TEST REPORT: IMPROVED

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44
Appendix

Calculation of the Refrigeration inches of corkboard beneath the

Requirements of a Theoretical concrete wearing surface.

'^'^'^* Refrigeration Requirements

When planning a new plant or xhe refrigeration requirements

determining the capacity of an ^^f ^his plant when operated at caexistmg one all sources of heat have -^ ^^^i¿ be as follows :

to be considered. As an example

consider the refriö-eration require- Removal of field heat:

ments of the following theoretical ''^^^Z^ZTZ:::^ B,.u.

plant: 44° Y.

44 (°TR)X 112,000

Plant Design and Operation (lbs.) x0.82(S)__- 4,040,960

. . , , , 1,1 Boxes, 4,000 lugs reduced A smgle-story storage plant ad- 44°

joins a packing room and contains 44 (°TR)X 16,000

three 40- by 50-foot storage rooms (Ibs.)x0.33 (S)___- 282,320

with 18-foot ceilings for multiple- 24 hours in storage after

pallet stacking. Each storage room ^^^So lugs reduced

will hold approximately 22,000 lugs 5°

of grapes. The plant also contains 5 (°TR) X 112,000

two 22- by 26-foot precooling (lbs.) XO.82 (S) 4e59,200

rooms with 12-foot ceilings, each of Boxes, 4,000 lugs reduced

which hold 4,000 lugs of fruit. ^°; .o.^.j.x ^^^ooo

Since the maximum capacity of the * ^ (lbs fx083 (S) 26 400

packing room is 4,000 lugs of grapes ' " ' " '

per day, one precooling room is Total field heat per

filled each day during the peak sea- day 4, 758,880

son. The precooling period is 24 Heat of respiration :

hours and, durins: the warmest part "^'^^i?^ ,1"^^ J^^. Tbompson «,i ' jî-xx ^ ' Seedless during precool- of the season, fruit temperature is ¿^.g ^t an average temreduced from an average of 80° F. to perature of 53° F.

36° F. during precooling. At the 56 (tons)xl,690

end of the harvest season the plant (B.t.u. per ton per

contains a peak storage load of ^^r.<^,.^^^^ ~~T~r^Z 94,640 ^7A c\f\i\ 1 rr<\ ^ A.' ^ ' 30,000 lugs of Thompson 74,000 lugs. The plant is mechani- seedless in storage durcally refrigerated with individual ing peak of receiving searoom dry-coil bunkers. Each stor- son, average 32°.

age room has five i/^-horsepower fan "^^^^ ^ ^^^^^ ^ '^'^^^

motors which deliver air at a total day)^ ^-T __^_^_^!! 180, 600

rate of 22,500 c.f.m. Each precool- '-

ing room has three li/^-horsepower Total vital heat per

fan motors which, when operated f-¡ se"o°Z.f!!': 275,240

tor precooling, move a total of 74^000 lugs of Emperor in

27,000 c.f.m of air. Exterior walls storage at end of packing

are insulated with 6 inches and the ^^^^^^i ^/T^^^f^^^-°;

ceiling with 8 inches of shredded ' (s.t.u^^^^per ton per

redAYood bark. The floor has 4 day) 362,600

45
Heat leakage: BJ.u.

Exterior wall surfaces,

7,920 square feet.

7,920 (sq. ft.)X48

(°TD)X1.03 (B.tu.

per day) 391, 565

Ceiling surface, 7,144

square feet.

7,144 (sq. ft.)X54

(°TD)X0.77 (B.tu.

per day) 297,048

Floor surface, 7,144 square

feet.

7,144 (sq. ft.)X35

(°TD)X1.6 (B.tu.

per day) 400, 064

Total heat leakage per

day - 1, 088, 677

Air infiltration :

One 8x8 foot outside door

in each room.

Storage room doors are

open average of 2

hours daily.

Precooling room doors are

open average of 4

hours daily.

14 (open-door hrs.)

X 250,000 (B.tu. per

hr. ) 3, 500, 000

Other heat sources :

Electric fan motors, 15 V2-

HP and 6 li/.-HP.

1G.5 (total HP) X3,000 B.tu.

(B.tu. per hr.)X24

(hrs.) 1,188,000

Electric lights, 32 200-w

lamps.

6.4 (KW) X 3,500

(B.t.u. per hr.)X6

(hra) 134,400

Workmen, 2 for 8 hours

per day.

2 (men) X 1,000 (B.t.u.

per hr.)X8 (hrs.)__ 16,000

2 (1-ton electric fork

truck X 35,000

(B.t.u. per 8

hrs.) 70,000

Total from incidental sources per

day 1, 408, 400

Recapitulation :

Field heat (peak load)— 4,758,880

Heat of respiration (receiving period) 275, 240

Heat leakage through external surfaces 1, 088, 677

Air infiltration (peak

load)_-_: 3,500,000

Other heat sources 1,408,400

Total 11, 031,197

11,031,197 (B.tu.)-^-288,000

(B.t.u. per ton) =38.3

tons of refrigeration.

46