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.