Previous Page Table of Contents Next Page


Section 7: Storage of horticultural crops


Recommended storage temperatures
Compatibility groups for storage of fruits, vegetables and floral crops
Storage practices
Storage structures
Dried and bulb crops
Root and tuber crops
Potatoes
Controlled atmosphere (C.A.) storage
Relative perishability and storage life of fresh horticultural crops

If produce is to be stored, it is important to begin with a high quality product. The lot of produce must not contain damaged or diseased units, and containers must be well ventilated and strong enough to withstand stacking. In general proper storage practices include temperature control, relative humidity control, air circulation and maintenance of space between containers for adequate ventilation, and avoiding incompatible product mixes.

Commodities stored together should be capable of tolerating the same temperature, relative humidity and level of ethylene in the storage environment. High ethylene producers (such as ripe bananas, apples, cantaloupe) can stimulate physiological changes in ethylene sensitive commodities (such as lettuce, cucumbers, carrots, potatoes, sweet potatoes) leading to often undesirable color, flavor and texture changes.

Temperature management during storage can be aided by constructing square rather than rectangular buildings. Rectangular buildings have more wall area per square feet of storage space, so more heat is conducted across the walls, making them more expensive to cool. Temperature management can also be aided by shading buildings, painting storehouses white or silver to help reflect the sun's rays, or by using sprinkler systems on the roof of a building for evaporative cooling. The United Nations' Food and Agriculture Organization (FAO) recommends the use of ferrocement for the construction of storage structures in tropical regions, with thick walls to provide insulation. Facilities located at higher altitudes can be effective, since air temperature decreases as altitude increases. Increased altitude therefore can make evaporative cooling, night cooling and radiant cooling more feasible. Underground storage for citrus crops is common in Southern China, while in Northwest China, apples are stored in caves (Liu, 1988). This system was widely used in the U.S. during the early pert of this century.

Certain commodities, such as onions and garlic, store better in lower relative humidity environments. Curing these crops and allowing the external layers of tissue to dry out prior to handling and storage helps to protect them from further water loss.

The air composition in the storage environment can be manipulated by increasing or decreasing the rate of ventilation (introduction of fresh air) or by using gas absorbers such as potassium permanganate or activated charcoal. Large-scale controlled or modified atmosphere storage requires complex technology and management skills, however, some simple methods are available for handling small volumes of produce.

Recommended storage temperatures

Recommended Temperature and Relative Humidity, and Approximate Transit and Storage Life for Fruits and Vegetable Crops (see Hardenburg et al, 1986 for more complete information on individual crops).

Product

Temperature

Relative Humidity (percent)

Approximate storage life

°C

°F

Amaranth

0-2

32-36

95-100

10-14 days

Anise

0-2

32-36

90-95

2-3 weeks

Apples

-1-4

30-40

90-95

1-12 months

Apricots

-0.5-0

31-32

90-95

1-3 weeks

Artichokes, globe

0

32

95-100

2-3 weeks

Asian pear

1

34

90-95

5-6 months

Asparagus

0-2

32-35

95-100

2-3 weeks

Atemoya

13

55

85-90

4-6 weeks

Avocados, Fuerte, Hass

7

45

85-90

2 weeks

Avocados, Lula, Booth-1

4

40

90-95

4-8 weeks

Avocados, Fuchs, Pollock

13

55

85-90

2 weeks

Babaco

7

45

85-90

1-3 weeks

Bananas, green

13-14

56-58

90-95

14 weeks

Barbados cherry

0

32

85-90

7-8 weeks

Bean sprouts

0

32

95-100

7-9 days

Beans, dry

4-10

40-50

40-50

6-10 months

Beans, green or snap

4-7

4045

95

7-10 days

Beans, lima, in pods

5-6

4143

95

5 days

Beets, bunched

0

32

98-100

10-14 days

Beets, topped

0

32

98-100

4-6 months

Belgian endive

2-3

36-38

95-98

24 weeks

Bitter melon

12-13

53-55

85-90

2-3 weeks

Black sapote

13-15

55-60

85-90

2-3 weeks

Blackberries

-0.5-0

31-32

90-95

2-3 days

Blood orange

4-7

4044

90-95

3-8 weeks

Blueberries

-0.5-0

31-32

90-95

2 weeks

Bok choy

0

32

95-100

3 weeks

Boniato

13-15

55-60

85-90

4-5 months

Breadfruit

13-15

55-60

85-90

2-6 weeks

Broccoli

0

32

95-100

10-14 days

Brussels sprouts

0

32

95-100

3-5 weeks

Cabbage, early

0

32

98-100

3-6 weeks

Cabbage, late

0

32

98-100

5-6 months

Cactus Leaves

24

3640

90-95

3 weeks

Cactus Pear

24

36-40

90-95

3 weeks

Caimito

3

38

90

3 weeks

Calabaza

10-13

50-55

50-70

2-3 months

Calamondin

9-10

48-50

90

2 weeks

Canistel

13-15

55-60

85-90

3 weeks

Cantaloups (3/4-slip)

2-5

36-41

95

15 days

Cantaloups (full-slip)

0-2

32-36

95

5-14 days

Carambola

9-10

48-50

85-90

3-4 weeks

Carrots, bunched

0

32

95-100

2 weeks

Carrots, mature

0

32

98-100

7-9 months

Carrots, immature

0

32

98-100

4-6 weeks

Cashew apple

0-2

32-36

85-90

5 weeks

Cauliflower

0

32

95-98

34 weeks

Celeriac

0

32

97-99

6-8 months

Celery

0

32

98-100

2-3 months

Chard

0

32

95-100

10-14 days

Chayote squash

7

45

85-90

4-6 weeks

Cherimoya

13

55

90-95

2-4 weeks

Cherries, sour

0

32

90-95

3-7 days

Cherries, sweet

-1 to -0.5

30-31

90-95

2-3 weeks

Chinese broccoli

0

32

95-100

10-14 days

Chinese cabbage

0

32

95-100

2-3 months

Chinese long bean

4-7

40-45

90-95

7-10 days

Clementine

4

40

90-95

24 weeks

Coconuts

0-1.5

32-35

80-85

1-2 months

Collards

0

32

95-100

10-14 days

Corn, sweet

0

32

95-98

5-8 days

Cranberries

2-4

36-40

90-95

24 months

Cucumbers

10-13

50-55

95

10-14 days

Currants

-0.5-0

31-32

90-95

1-4 weeks

Custard apples

5-7

41-45

85-90

4-6 weeks

Daikon

0-1

32-34

95-100

4 months

Dates

-18 or 0

0 or 32

75

6-12 months

Dewberries

-0.5-0

31-32

90-95

2-3 days

Durian

4-6

39-42

85-90

6-8 weeks

Eggplants

12

54

90-95

1 week

Elderberries

-0.5-0

31-32

90-95

1-2 weeks

Endive and escarole

0

32

95-100

2-3 weeks

Feijoa

5-10

41-50

90

2-3 weeks

Figs fresh

-0.5-0

31-32

85-90

7-10 days

Garlic

0

32

65-70

6-7 months

Ginger root

13

55

65

6 months

Gooseberries

-0.5-0

31-32

90-95

34 weeks

Granadilla

10

50

85-90

3-4 weeks

Grapefruit, Calif. & Ariz.

14-15

58-60

85-90

6-8 weeks

Grapefruit, Fla. & Texas

10-15

50-60

85-90

6-8 weeks

Grapes, Vinifera

-1 to -0.5

30-31

90-95

1-6 months

Grapes, American

-0.5-0

31-32

85

2-8 weeks

Greens, leafy

0

32

95-100

10-14 days

Guavas

5-10

41-50

90

2-3 weeks

Haricot vert

4-7

4045

95

7-10 days

Horseradish

-1-0

30-32

98-100

10-12 months

Jaboticaba

13-15

55-60

90-95

2-3 days

Jackfruit

13

55

85-90

2-6 weeks

Jaffa orange

8-10

46-50

85-90

8-12 weeks

Japanese eggplant

8-12

46-54

90-95

1 week

Jerusalem Artichoke

-0.5-0

31-32

90-95

+5 months

Jicama

13-18

55-65

65-70

1-2 months

Kale

0

32

95-100

2-3 weeks

Kiwano

10-15

50-60

90

6 months

Kiwifruit

0

32

90-95

3-5 months

Kohlrabi

0

32

98-100

2-3 months

Kumquats

4

40

90-95

2-4 weeks

Langsat

11-14

52-58

85-90

2 weeks

Leeks

0

32

95-100

2-3 months

Lemons

10-13

50-55

85-90

1-6 months

Lettuce

0

32

98-100

2-3 weeks

Limes

9-10

48-50

85-90

6-8 weeks

Lo bok

0-1.5

32-35

95-100

24 months

Loganberries

-0.5-0

31-32

90-95

2-3 days

Longan

1.5

35

90-95

3-5 weeks

Loquats

0

32

90

3 weeks

Lychees

1.5

35

90-95

3-5 weeks

Malanga

7

45

70-80

3 months

Mamey

13-15

55-60

90-95

2-6 weeks

Mangoes

13

55

85-90

2-3 weeks

Mangosteen

13

55

85-90

2-4 weeks

Melons:


Casaba

10

50

90-95

3 weeks


Crenshaw

7

45

90-95

2 weeks


Honeydew

7

45

90-95

3 weeks


Persian

7

45

90-95

2 weeks

Mushrooms

0

32

95

34 days

Nectarines

-0.5-0

31-32

90-95

2-4 weeks

Okra

7-10

45-50

90-95

7-10 days

Olives, fresh

5-10

41-50

85-90

+6 weeks

Onions, green

0

32

95-100

34 weeks

Onions, dry

0

32

65-70

1-8 months

Onion sets

0

32

65-70

6-8 months

Oranges, Calif. & Ariz.

3-9

3848

85-90

3-8 weeks

Oranges, Fla. & Texas

0-1

32-34

85-90

8-12 weeks

Papayas

7-13

45-55

85-90

1-3 weeks

Passionfruit

7-10

45-50

85-90

3-5 weeks

Parsley

0

32

95-100

2-2.5 months

Parsnips

0

32

95-100

+6 months

Peaches

-0.5-0

31-32

90-95

2-4 weeks

Pears

-1.5 to -0.5

29-31

90-95

2-7 months

Peas, green

0

32

95-98

1-2 weeks

Peas, southern

+5

4041

95

6-8 days

Pepino

4

40

85-90

1 month

Peppers, Chili (dry)

0-10

32-50

60-70

6 months

Peppers, sweet

7-13

45-55

90-95

2-3 weeks

Persimmons, Japanese

-1

30

90

34 months

Pineapples

7-13

45-55

85-90

24 weeks

Plantain

13-14

55-58

90-95

1-5 weeks

Plums and prunes

-0.5-0

31-32

90-95

2-5 weeks

Pomegranates

5

41

90-95

2-3 months

Potatoes, early crop

10-16

50-60

90-95

10-14 days

Potatoes, late crop

4.5-13

40-55

90-95

5-10 months

Pummelo

7-9

4548

85-90

12 weeks

Pumpkins

10-13

50-55

50-70

2-3 months

Quinces

-0.5-0

31-32

90

2-3 months

Raddichio

0-1

32-34

95-100

2-3 weeks

Radishes, spring

0

32

95-100

34 weeks

Radishes, winter

0

32

95-100

24 months

Rambutan

12

54

90-95

1-3 weeks

Raspberries

-0.5-0

31-32

90-95

2-3 days

Rhubarb

0

32

95-100

24 weeks

Rutabagas

0

32

98-100

+6 months

Salsify

0

32

95-98

2-4 months

Santol

7-9

45-48

85-90

3 weeks

Sapodilla

16-20

60-68

85-90

2-3 weeks

Scorzonera

0-1

32-34

95-98

6 months

Seedless cucumbers

10-13

50-55

85-90

10-14 days

Snow peas

0-1

32-34

90-95

1-2 weeks

Soursop

13

55

85-90

1-2 weeks

Spinach

0

32

95-100

10-14 days

Squashes, summer

5-10

41-50

95

1-2 weeks

Squashes, winter

10

50

50-70

2-3 months

Strawberries

0

32

90-95

5-7 days

Sugar apples

7

45

85-90

4 weeks

Sweetpotatoes

13-15

55-60

85-90

4-7 months

Tamarillos

3-4

37-40

85-95

10 weeks

Tamarinds

7

45

90-95

3-4 weeks

Tangerines, mandarins, and related citrus fruits

4

40

90-95

24 weeks

Taro root

7-10

45-50

85-90

4-5 months

Tomatillos

13-15

55-60

85-90

3 weeks

Tomatoes, mature-green

18-22

65-72

90-95

1-3 weeks

Tomatoes, firm-ripe

13-15

55-60

90-95

4-7 days

Turnips

0

32

95

4-5 months

Turnip greens

0

32

95-100

10-14 days

Ugli fruit

4

40

90-95

2-3 weeks

Waterchestnuts

0-2

32-36

98-100

1-2 months

Watercress

0

32

95-100

2-3 weeks

Watermelons

10-15

50-60

90

2-3 weeks

White sapote

19-21

67-70

85-90

2-3 weeks

White asparagus

0-2

32-36

95-100

2-3 weeks

Winged bean

10

50

90

4 weeks

Yams

16

61

70-80

6-7 months

Yucca root

0-5

32-41

85-90

1-2 months

Source: McGregor, B.M. 1989. Tropical Products Transport Handbook. USDA Office of Transportation, Agricultural Handbook 668.

Compatibility groups for storage of fruits, vegetables and floral crops

Group 1: Fruits and vegetables, 0 to 2°C (32 to 36°F), 90-95% relative humidity. Many products in this group produce ethylene.

apples

grapes (without

parsnips

apricots

sulfur dioxide)

peaches

Asian pears

horseradish

pears

Barbados cherry

kohlrabi

persimmons

beets, topped

leeks

plums

berries (except

longan

pomegranates

cranberries)

loquat

prunes

cashew apple

lychee

quinces

cherries

mushrooms

radishes

coconuts

nectarines

rutabagas

figs (not with apples)

oranges* (Florida and Texas)

turnips

*Citrus treated with biphenyl may give odors to other products

Group 2: Fruits and vegetables, 0 to 2°C (32 to 36°F), 95-100% relative humidity. Many products in this group are sensitive to ethylene.

Amaranth*

corn, sweet*

parsley*

anise

daikon*

parsnips*

artichokes*

endive*

peas*

asparagus

escarole*

pomegranate

bean sprouts

grapes (without sulfur dioxide)

raddichio

beets*


radishes*

Belgian endive

horseradish

rhubarb

berries (except cranberries)

Jerusalem artichoke

rutabagas*


kiwifruit

salsify

bok choy

kohlrabi*

scorzonera

broccoli*

leafy greens

snow peas

brussels sprouts*

leeks' (not with figs or grapes)

spinach*

cabbage*


turnips*

carrots*

lettuce

waterchestnut

cauliflower

lo bok

watercress*

celeriac*

mushrooms


celery*

onions, green* (not with figs, grapes, mushrooms, rhubarb, or corn)


cherries



* these products can be top-iced

Group 3: Fruits and vegetables, 0 to 2°C (32 to 36°F), 65-75% relative humidity. Moisture will damage these products.

Garlic

onions, dry

Group 4: Fruits and vegetables, 4.5°C (40°F), 90-95% relative humidity.

cactus leaves

lemons*

tamarillo

cactus pears

lychees

tangelos*

caimito

kumquat

tangerines*

cantaloupes**

mandarin*

ugli fruit*

clementine

oranges (Calif. and Arizona)

yucca root

cranberries

pepino


* citrus treated with biphenyl may give odors to other products.
** can be top-iced.

Source: McGregor, B.M. 1989. Tropical Products Transport Handbook. USDA Office of Transportation, Agricultural Handbook 668.

Group 5: Fruits and vegetables, 10°C (50°F), 85-90% relative humidity. Many of these products are sensitive to ethylene. These products also are sensitive to chilling injury.

beans

kiwano

pummelo

calamondin

malanga

squash, summer

chayote

okra

(sot shell)

cucumber

olive

tamarind

eggplant

peppers

taro root

haricot vert

potatoes, storage


Group 6: Fruits and vegetables, 13 to 15°C (55 to 60°F), 85-90% relative humidity. Many of these products produce ethylene. These products also are sensitive to chilling injury.

atemoya

granadilla

papayas

avocados

grapefruit

passionfruit

babaco

guava

pineapple

bananas

jaboticaba

plantain

bitter melon

jackfruit

potatoes, new

black sapote

langsat

pumpkin

boniato

lemons*

rambutan

breadfruit

limes*

santol

canister

mamey

soursop

carambola

mangoes

sugar apple

cherimoya

mangosteen

squash, winter

coconuts

melons (except cantaloupes)

(hard shell)

feijoa


tomatillos

ginger root


tomatoes, ripe

*citrus treated with biphenyl may give odors to other products

Group 7: Fruits and vegetables, 18 to 21°C (65 to 70°F), 85-90% relative humidity.

jicama

sweetpotatoes*

watermelon*

pears

tomatoes,

white sapote

(for ripening)

mature green

yams*

*separate from pears and tomatoes due to ethylene sensivity.

Group 8: Flowers and florist greens, 0 to 2°C (32 to 36°F), 90-95% relative humidity.

allium

freesia

peony, tight

aster, China

gardenia

buds

bouvardia

hyacinth

ranunculus

carnation

iris, bulbous

rose

chrysanthemum

lily

squill

crocus

lily-of-the-valley

sweet pea

cymbidium orchid

narcissus

tulip

adiantum (maidenhair)

ground pine

rhododendren

cedar

flex (holly)

salal (lemon leaf)

dagger and wood

juniper


ferns

mistletoe

vaccinium

galax

mountain-laurel

(huckleberry)

woodwardia fern



Source: McGregor, B.M. 1989. Tropical Products Transport Handbook. USDA Office of Transportation, Agricultural Handbook 668.

Group 9: Flowers and florist greens, 4.5°C (40°F), 90-95% relative humidity.

acacia

delphinium

orchid,

alstromeria

feverfew

cymbidium

anemone

forget-me-not

ornithogalum

aster, China

foxglove

poppy

buddleia

gaillardia

phlox

calendula

gerbera

primrose

calla

gladiolus

protect

candytuft

gloriosa

ranunculus

clarkia

gypsophilla

snapdragon

columbine

heather

snowdrop

coreopsis

laceflower

statice

cornflower

lilac, forced

stephanotis

cosmos

lupine

stevia

dahlia

marigolds

stock

daisies

mignonette

strawflower

violet

zinnia


adiantum (maidenhair)

eucalyptus

myrtus (myrtle)

asparagus (plumosa, sprenger)

hedera

philodendren

flex (holly)

pittosporum

buxus (boxwood)

leatherleaf (baker fern)

pothos

camellia


scotch-broomern

croton

leucothoe, drooping

smilax, southern

dracaena

magnolia

woodwardia fern

Group 10: Flowers and florist greens, 7 to 10°C (45 to 50°F), 90-95% relative humidity.

anemone

eucharis

orchid, cattleya

bird-of-paradise

gloriosa

sweet william

camellia

godetia


chamaedora

cordyline (ti)

palm

podocarpus


Group 11: Flowers and florist greens, 13 to 15°C (55 to 60°F), 90-95% relative humidity.

anthurium

heliconia

poinsetta

ginger

orchid, vanda


diffenbachia

stag horn fern


Source: McGregor, B.M. 1989. Tropical Products Transport Handbook. USDA Office of Transportation, Agricultural Handbook 668.

Storage practices

Inspecting stored produce and cleaning storage structures on a regular basis will help reduce losses by minimizing the buildup of pests and discouraging the spread of diseases.

Inspect produce and clean the storage structure:

Clean and maintain the storage structure:

Source: FAO. 1985. Prevention of Post-Harvest Food Losses: A Training Manual. Rome: UNFAO. 120pp.

Storage facilities should be protected from rodents by keeping the immediate area clean, free from trash and weeds. Rat guards can be made from simple materials such as old tin cans or pieces of sheet metal fashioned to fit the extended legs of storage structures. If desired, more elaborate technologies can be used. Concrete floors will help prevent rodent entry, as will screens on windows, vents and drains.

Remove trash and weeds:

Rat guards:

Screens:

Cement floors:

Source: FAO. 1985. Prevention of Post-Harvest Food Losses: A Training Manual. Rome: UNFAO. 120 pp.

When inspecting stored produce, any spoiled or infected produce should be removed and destroyed. In some cases, produce may still be fit for consumption if used immediately perhaps as animal feed. Reusable containers and sacks should be disinfected in chlorinated or boiling water before reuse.

Disinfect used sacks:

Source: FAO. 1985. Prevention of Post-Harvest Food Losses: A Training Manual. Rome: UNFAO. 120pp.

Placing materials on the floor beneath sacks or cartons of produce prevents dampness from reaching produce suited to dry conditions in storage. This helps to reduce the chance of fungal infection, while also improving ventilation and/or sanitation in the storeroom. Some examples of useful materials follow:

Waterproof sheets:

Poles:

Wooden pallets:

Source: FAO. 1985. Prevention of Post-Harvest Food Losses: A Training Manual. Rome: UNFAO. 120 pp.

Storage structures

A yam barn is a traditional structure used in West Africa to store yams after curing. Fast-growing, live trees are used to create a rectangular structure, and form the framework of the barn as well as provide shade.

Outside view of barn with 'live' shade

Trunk of fast growing tree-planted in situ.

Inside of barn showing tying of yams

Source: Wilson, J. No date. Careful Storage of Yams: Some Basic Principles to Reduce Losses. London, England: Commonwealth Secretariat/International Institute of Tropical Agriculture.

Storage facilities require adequate ventilation in order to help extend shelf life and maintain produce quality. The following are three types of fans found in common use.

Centrifugal:

Axial flow:

Propeller/expeller:

Source: Potato Marketing Board. No date. Control of Environment. Part 2. London: Sutton Bridge Experiment Station, Report No. 6

Ventilation in storage structures is improved if air inlets are located at the bottom of the store, while air outlets are at the top. A simple, light-proof exhaust vent is a pressure-relief flap.

Source: Potato Marketing Board. No date. Control of Environment. Part 2. London: Sutton Bridge Experiment Station, Report No. 6

Any type of building or facility used for storage of horticultural crops should be insulated for maximum effectiveness. A well insulated refrigerated building will require less electricity to keep produce cool. If the structure is to be cooled by evaporative or night air ventilation, a well insulated building will hold the cooled air longer.

Insulation R-values are listed below for some common building materials. R refers to resistance, and the higher the R-value, the higher the material's resistance to heat conduction and the better the insulating property of the material.

R - Value

Material

1 inch thick

Batt and Blanket Insulation


Glass wool, mineral wool, or fiberglass

3.50

Fill-Type Insulation


Cellulose

3.50

Glass or mineral wool

2.50-3.00

Vermiculite

2.20

Wood shavings or sawdust

2.22

Rigid Insulation


Plain expanded extruded polystyrene

5.00

Expanded rubber

4.55

Expanded polystyrene molded beads

3.57

Aged expanded polyurethane

6.25

Glass fiber

4.00

Polyisocyranuate

8.00

Wood or cane fiber board

2.50

Foamed-in-Place Insulation


Sprayed expanded urethane

6.25

Building Materials

Full thickness of material

Solid concrete

0.08

8-inch concrete block, open core

1.11

8-inch lightweight concrete block open core

2.00

8-inch concrete block with vermiculite in core

5.03

Lumber, fir or pine

1.25

Metal siding

<0.01

3/8-inch plywood

1.25 - 0.47

1/2-inch plywood

1.25 - 0.62

Masonite particleboard

1.06

25/32-inch insulated sheathing

2.06

1/2-inch Sheetrock

0.45

1/2-inch wood lapsiding

0.81

Source: Boyette, M.D. et al. No date. Design of Room Cooling Facilities: Structural and Energy Requirements. North Carolina Agricultural Extension Service.

An evaporative cooler located in the peak of a storage structure can cool an entire room of stored produce such as sweetpotatoes or other chilling sensitive crops. The vents for outside air should be located at the base of the building so that cool air is circulated throughout the room before it can exit.

Source: Thompson, J.F. and Scheuerman, R.W. 1993. Curing and Storing California Sweetpotatoes. Merced County Cooperative Extension, Merced, California 95340

Illustrated below is a cross-sectional view of a storehouse for fruits. This system was officially approved as the standard model for farm-level storehouses by the Ministry of Construction (Korea) in 1983. Note that air inlets are at the base of the building, and the floor is perforated, allowing free movement of air. The entire building is set below ground level taking advantage of the cooling properties of soil.

Source: Seung Koo Lee, 1994. Assoc. Prof., Postharvest Technology Lab., Department of Horticulture, Seoul National University, Suwon 441-744, Korea.

Commercially constructed cold rooms can be quite expensive, but fortunately the small-scale operator has many choices. Cold rooms can be self-constructed, purchased as prefabricated units (new or used), or made from refrigerated transportation equipment such as railway cars, highway vans or marine containers. Illustrated below is the basic plan for a self-built cold room. For more detailed information about determining the cold room size best suited to your operation, evaluating choices when purchasing or building a cold room, refer to the source below.

Source: Thompson, J.F. and Spinoglio, M. 1994. Small-scale cold rooms for perishable commodities. Family Farm Series, Small Farm Center, University of California, Davis.

For storage facilities that are refrigerated, using outside air for ventilation is wasteful of energy. For these systems, a simple recirculation system can be designed by adding a fan below floor level and providing a free space at one end of the storeroom for cool air to return to the inlet vents.

Source: Potato Marketing Board. No date. Control of Environment. Part 2. London: Sutton Bridge Experiment Station, Report No. 6

The proper arrangement of floor vents for air circulation will improve ventilation in the storage house. Lateral ducts should be 2 meters apart when measured from center to center. Air How velocities from the main duct should be 10 to 13 meters/second.

Longitudinal main duct:

Central main duct:

Source: Potato Marketing Board. No date. Control of Environment. Part 2. London: Sutton Bridge Experiment Station, Report No. 6

Lateral ducts can be constructed of a variety of materials. Portable vents can be made from wooden slats, in a triangular, square or rectangular design. A round tube of plastic or clay can be used if holes can be drilled without causing structural damage, or permanent ducts can be constructed below ground, using concrete blocks.

Triangular wooden duct:

Clay pipe duct:

Sunken concrete duct:

Source: Potato Marketing Board. No date. Control of Environment. Part 2. London: Sutton Bridge Experiment Station, Report No. 6

In cooler regions, suitable storage temperatures can be maintained by bringing outside air into the storage facility. Typical fan installations for a pressurized ventilation system are illustrated below. Overhead distribution of air simplifies the storehouse design. A indoor recirculation inlet can be added if refrigeration is in use. Ducts can be constructed of wood, plastic tubing or any suitable materials.

Overhead ventilation distribution system:

Outdoor inlet versus indoor/outdoor inlet:

Types of ducts for air inlet fans:

Source: Davis, R. et al. No date. Storage Recommendations for Northern Onion Growers. Cornell University Extension Information Bulletin 148

Storage structures can be cooled by ventilating at night when outside air is cool. For best results, air vents should be located at the base of the storage structure. An exhaust fan located at the top of the structure pulls the cool air through the storeroom. Vents should be closed at sunrise, and remain closed during the heat of the day.

Overhanging roof extensions on storage structures are very helpful in shading the walls and ventilation openings from the sun's rays, and in providing protection from rain. An overhang of at least 1 meter (3 feet) is recommended.

Source: Walker, D.J. 1992. World Food Programme Food Storage Manual. Chatham, UK: Natural Resources Institute.

Where electricity is not available, wind-powered turbines can help keep storerooms cool by pulling air up through the building. Vents at the floor level are especially useful for cooling via night air ventilation.

The turbine illustrated below can be constructed of sheet metal that is twisted to catch the wind, and attached to a central pole that acts as the axis of rotation. Warm air in the storage room rises, causing the turbine to rotate, expelling the air and initiating an upward flow of warm air. The turbine should be placed on the peak of the roof of a storage structure.

Protected surface storage is a simple method for storing small quantities of produce. The examples illustrated below are especially good for storage when night temperatures are lower than that desired for proper storage. Insulating materials such as straw can be used and protective covers can be constructed from wooden planks, plastic sheeting or layers of compacted soil.

Cone-shaped pit storage:

Mound storage:

Trench storage:

Source: McKay, S. 1992. Home Storage of Fruits and Vegetables. Northest Regional Agricultural Engineering Service Publication No. 7

One of the simplest methods for storing small quantities of produce is to use any available container, and create a cool environment for storage by burying the container using insulating materials and soil. The example provided here employs a wooden barrel and straw for insulation.

Storage barrel:

Source: Bubel, M. and Bubel, N. 1979. Root Cellaring: The Simple. No-Processing Way to Store Fruits and Vegetables. Emmaus, PA: Rodale Press. 297 pp.

A root cellar can be constructed by digging out a pit to a depth of about 2 meters (7 to 8 feet) and framing the sides with wooden planks. The example illustrated here is about 3 by 4 meters (12 by 15 feet) in size, with a 35 cm square (one foot square) wooden chute as a roof vent

Source: Bubel, M. and Bubel, N. 1979. Root Cellaring: The Simple. No-Processing Way to Store Fruits and Vegetables. Emmaus, PA: Rodale Press. 297 pp.

An outdoor storage bin can serve as a place to keep small quantities of potatoes in a region with a cool but not freezing climate. A wooden rack provides an air space for ventilation and straw provides insulation. The best location for such a structure would be in a shady spot.

Storage bin:

A root box, lined with hardware cloth and straw, buried to the top edge in soil will keep potatoes cool wile providing protection from freezing. The wooden lid can be lifted for easy access to produce, and straw bales on top provide more insulation.

Root box:

Source: Bubel, M. and Bubel, N. 1979. Root Cellaring: The Simple No-Processing Way to Store Fruits and Vegetables. Emmaus, PA: Rodale Press. 297 pp.

Dried and bulb crops

Onions, garlic and dried produce are best suited to low humidity in storage. Onions and garlic will sprout if stored at intermediate temperatures. Pungent types of onions will store longer than mild onions, which are rarely stored for more than one month (Kasmire & Cantwell in Kader, 1992). The following table lists the storage conditions recommended for these crops.

 

Temperature

RH

Potential storage duration

C

F

%

Onions

0-5

32-41

65-70

6-8 months

28-30

82-86

65-70

1 month

Garlic

0

32

70

6-7 months

28-30

82-86

70

1 month

Dried fruits and vegetables

<10

<50

55-60

6-12 months

Source: Bubel, M. and Bubel, N. 1979. Root Cellaring: The Simple No-Processing Way to Store Fruits end Vegetables. Emmaus, PA: Rodale Press. 297 pp.

For bulk storage of onions or garlic, ventilation systems should be designed to provide air into the store from the bottom of the room at a rate of 2 cubic feet per minute per cubic feet of produce. If produce is in cartons or bins, stacks must allow free movement of air. Rows of containers should be stacked parallel to the direction of the flow of air and be spaced six to seven inches apart. An adequate air supply must be provided at the bottom of each row and containers must be properly vented.

Bulk storage:

Storage in cartons or bins:

Source: Oregon State University, 1978. Onion Storage: Guidelines for Commercial Growers. Oregon State Extension Service. Extension Circular 948.

Root and tuber crops

The recommended storage conditions for root and tuber crops are listed in the following table (from Kasmire & Cantwell in Kader, 1992). Potatoes for processing are best kept at intermediate temperatures to limit the production of sugars which darken when heated during processing. Potatoes meant for consumption must also be stored in the dark, since the tubers will produce chlorophyll (turning green) and develop the toxic alkaloid solanine if kept in the light. Potatoes stored for use as "seed" are best stored in diffuse light (CIP, 1981). The chlorophyll and solanine that accumulate will aid to protect the seed potatoes from insect pests and decay organisms.

Tropical root and tuber crops must be stored at temperatures that will protect the crops from chilling, since chilling injury can cause internal browning, surface pitting and increased susceptibility to decay.

 

Temperature

RH(%)

Potential storage duration

C

F

Potatoes





Fresh market

4-7

39-45

95-98

10 months

Processing

8-12

47-54

95-98

10 months

Seed potatoes

0-2

32-36

95-98

10 months

Cassava

5-8

41-47

80-90

2-4 weeks

0-5

32-41

85-95

6 months

Sweetpotato

12-14

54-58

85-90

6 months

Yam

13-15

55-59

near 100

6 months

27-30

80-86

60-70

3-5 weeks

Ginger

12-14

54-58

65-75

6 months

Jicama

12-15

54-59

65-75

3 months

Taro

13-15

55-59

85-90

4 months

Potatoes

When storing potatoes, a field storage clamp is a low cost technology that can be designed using locally available materials for ventilation and insulation. The example illustrated here employs a wooden ventilator box and straw for insulation. The entire pile of potatoes and straw is covered with a layer of soil, which should not be highly compacted. In very cold regions, a second layer of straw and soil can be added. In hot regions, less soil is needed, but more ventilation can be added by constructing chimney type air outlets at the top of the clamp.

Field storage clamp:

Source: CIP. 1981. Principles of Potato Storage. Lima, Peru: International Potato Center (CIP). 105 pp.

Simple storage houses for potatoes can be constructed for small quantities of produce. The examples provided here can store 1 to 2 metric tons, and are used on farms and in mountain villages. The first is made from unfinished wooden planks painted white to reduce heat accumulation from the sun and covered with a large thatched roof for protection from sun and rain. It has a large door on one side for loading and unloading.

The second storage house is constructed from lath and plaster and mud bricks in a cylindrical form. It has two doors, one on top for loading, the other at the bottom for easy removal of potatoes for sale or consumption. White-wash helps reduce heat accumulation and a thatch roof protects the potatoes from rain and sun.

Source: CIP. 1981. Principles of Potato Storage. Lima, Peru: International Potato Center (CIP). 105 pp.

For large quantities of potatoes, a self-supporting A-frame storehouse can be constructed. A pit is dug about 10 feet deep and wooden air ducts are placed along the earthen floor. The roof of the building is constructed of wood, then covered with straw and soil.

Source: University of Idaho. No date. Idaho Potato Storage. Agricultural Experiment Station, College of Agriculture, Bulletin 410.

Ducts for ventilation of bulk storage rooms can be laid out vertically as well as horizontally. The storeroom for potatoes shown below provides for plenty of ventilation using simple materials. The room can be of any size or shape since air ducts can be positioned to extend evenly throughout.

Source: Lopez, E.G. 1983. Conservación de la Producción Agrícola. Barcelona: Editorial Aedos. 188 pp.

When loading potatoes into bulk storage, even distribution of the produce is important for proper ventilation. Uneven loads will inhibit air movement and result in storage losses due to inadequate ventilation.

Even distribution of potatoes in the storeroom:

Uneven distribution of potatoes in the storeroom:

Source: CIP. 1981. Principles of Potato Storage. Lima, Peru: International Potato Center (CIP) 105 pp.

Controlled atmosphere (C.A.) storage

Controlled or modified atmosphere storage should be used as a supplement to, and not as a substitute for, proper temperature and relative humidity management. Some simple methods for modifying the composition of air in the storage environment are listed below (from Kader, 1992). Air coming into the storeroom or being recirculated within the room must pass through a monitoring and control system.

Oxygen gas control:

to DECREASE:

purging with nitrogen

from liquid nitrogen through an evaporator
from a membrane system nitrogen generator
from a molecular sieve system nitrogen generator

Carbon dioxide control:

to INCREASE:

dry ice
pressurized gas cylinder

to DECREASE:

molecular sieve scrubber
activated charcoal scrubber
sodium hydroxide scrubber
hydrated lime (use 0.6 kg of hydrated lime to treat the air used to ventilate 100 kg of fruit Air can be directed to pass through a box, located inside or outside the C.A. storeroom).

Ethylene control:

to DECREASE:

potassium permanganate
activated charcoal
catalytic oxidation

Source: Vigneault, C., Raghavan, V.G.S., and Prange, R. 1994. Techniques for controlled atmosphere storage of fruits and vegetables. Research Branch, Agriculture and Agri-Food Canada, Technical Bulletin 1993-18E.

The following table is a summary of recommended conditions for controlled atmosphere storage (from Kader, 1992). Only fruits and vegetables for which commercial uses of C.A. storage are common have been included.

 

Temperature range

%O2 range

%CO2 range

C

F

Strawberry

0-5

32-41

10

15-20

Apple

0-5

32-41

2-3

1-2

Kiwifruit

0-5

32-41

2

5

Nuts and dried fruits

0-25

32-77

0-1

0-100

Bananas

12-15

54-59

2-5

2-5

Cantaloupe

3-7

38-45

3-5

10-15

Lettuce

0-5

32-41

2-5

0

Tomatoes





Mature green

12-20

54-68

3-5

0

Partially-ripe

8- 12

47-54

3-5

0

Illustrated here is a model of a small-scale commercial C.A. storage room. Each component is labelled. For farther information on construction methods, materials, and costs, please refer to the source listed below.

Source: Lougheed, E.C. et al. 1985. Small scale simulated commercial C.A. Storage rooms. Int'l. CA Conf. North Carolina State Univ. Hort. Report No. 126:235-247.

Controlled atmosphere storage of pallet loads of produce is also possible using a more permanent set-up for creating a gas-seal. Any number of pallets can be accomodated inside a plastic tent. A small trough constructed of sheet metal is laid in a rectangular pattern into a concrete floor of a storage structure. A 7-mil polyethylene sheet is put over the pallet load of produce, and the sheet is sealed by pushing a long piece of rubber tubing into the trough.

Typical layout of a C.A. tent:

Layout of a seal in the trough on the storeroom floor:

Source: McDonald, B. 1982. Controlled atmosphere storage using plastic tents. International Institute of Refrigeration.

A low cost plastic tent fashioned from clear polyethylene sheeting can be used for controlled atmosphere storage of bunches of green bananas. A small fan serves to circulate the C.A. storage air (2% O2 and 5% CO2) through a chamber of potassium permanganate on aluminum oxide (Purafil). Ripening is delayed as ethylene is scrubbed from the storage air. The shelf life of bananas under these conditions is four to six weeks at ambient temperatures.

Source: Shorter, A.J. et al. 1987. Controlled atmosphere storage of bananas in bunches at ambient temperatures. CSIRO Food Research Quarterly 47:61-63.

Relative perishability and storage life of fresh horticultural crops

Classification of fresh horticultural crops according to their relative perishability and potential storage life in air at near optimum temperature and relative humidity.

RELATIVE PERISHABILITY

POTENTIAL STORAGE LIFE (WEEKS)

COMMODITIES

Very high

<2

Apricot, blackberry, blueberry, cherry, fig, raspberry, strawberry; asparagus, bean sprouts, broccoli, cauliflower, green onion, leaf lettuce, mushroom, muskmelon, pea, spinach, sweet corn, tomato (ripe); most cut flowers and foliage; minimally processed fruits and vegetables.

High

2-4

Avocado, banana, grape (without SO2 treatment), guava, loquat, mandarin, mango, melons (honeydew, crenshaw, Persian), nectarine, papaya, peach, plum; artichoke, green beans, Brussels sprouts, cabbage, celery, eggplant, head lettuce, okra, pepper, summer squash, tomato (partially ripe).

Moderate

4- 8

Apple and pear (some cultivars), grape (SO2-treated), orange, grapefruit, lime, kiwifruit, persimmon, pomegranate; table beet, carrot, radish, potato (immature).

Low

8-16

Apple and pear (some cultivars), lemon; potato (mature), dry onion, garlic, pumpkin, winter squash, sweet potato, taro, yam; bulbs and other propagules of ornamental plants.

Very low

>16

Tree nuts, dried fruits and vegetables

Source: Kader, A.A, 1993. Postharvest Handling. In: Preece, J.E. and Read, P.E., The Biology of Horticulture- An Introductory Textbook. New York: John Wiley & Sons. pp. 353-377.


Previous Page Top of Page Next Page