To print a copy, we recommend downloading the (PDF) print version. (Download the free Adobe Acrobat Reader, if you don't already have it.)

Basket of vegetables

Postharvest Management of Commercial Horticultural Crops

STORAGE CONDITIONS
FRUITS & VEGETABLES
This bulletin was reprinted with permission from Kansas State University Cooperative Extension Service, Manhattan, KS. Written by Karen L. B. Gast, Extension specialist, Post Harvest and Marketing.



University of Maine Cooperative Extension
Bulletin #4135

Once a crop is harvested, it is almost impossible to improve its quality. Losses of horticultural crops due to improper storage and handling can range from 10 to 40 percent. Proper storage conditions�temperature and humidity�are needed to lengthen storage life and maintain quality once the crop has been cooled to the optimum storage temperature.

Fresh fruits and vegetables are living tissues, although they are no longer attached to the plant. They breathe, just as humans do, and their composition and physiology continue to change after harvest. They continue to ripen and, finally, they begin to die. Cellular breakdown and death (senescence) are inevitable, but can be slowed with optimal storage conditions. Fresh fruits and vegetables need low temperatures (32 to 55�F) and high relative humidities (80 to 95 percent) to lower respiration and to slow metabolic and transpiration rates. By slowing these processes, water loss is reduced and food value, quality and energy reserves are maintained.

Relative Humidity

Transpiration rates (water loss from produce) are determined by the moisture content of the air, which is usually expressed as relative humidity. At high relative humidity, produce maintains salable weight, appearance, nutritional quality and flavor, while wilting, softening and juiciness are reduced. Leafy vegetables with high surface-to-volume ratios; injured produce; and immature fruits and vegetables have higher transpiration rates. External factors affecting transpiration rates are temperature, relative humidity, air velocity and atmospheric pressure. High temperatures, low relative humidity and high air velocity increase transpiration rates.

Relative humidity needs to be monitored and controlled in storage. A hygrometer or a sling psychrometer, not the appearance of the produce, should be used to monitor humidity. Control can be achieved by a variety of methods:

  1. Operating a humidifier in the storage area.

  2. Regulating air movement and ventilation in relation to storage room load.

  3. Maintaining refrigeration coil temperature within 2�F of the storage room air temperature.

  4. Using moisture barriers in the insulation of the storage room or transport vehicle, and in the lining of the packing containers.

  5. Wetting the storage room floor.

  6. Using crushed ice to pack produce for shipment.

  7. Sprinkling leafy vegetables, cool-season root vegetables, and immature fruits and vegetables with water.

Table 1 lists the optimum relative humidity for the storage of several fruits and vegetables.

Temperature

Respiration and metabolic rates are directly related to room temperatures within a given range. The higher the rate of respiration, the faster the produce deteriorates. Lower temperatures slow respiration rates and the ripening and senescence processes, which prolongs the storage life of fruits and vegetables. Low temperatures also slow the growth of pathogenic fungi which cause spoilage of fruits and vegetables in storage. Table 2 contains a list of fruits and vegetables classified by respiration rates. Producers should give special care and attention to proper storage conditions for produce with high to extremely high respiration rates�those crops will deteriorate much more quickly.

It is impossible to make a single recommendation for cool storage of all fruits and vegetables. Climate of the area where the crop originated, the plant part, the season of harvest and crop maturity at harvest are important factors in determining the optimum temperature. A general rule for vegetables is that cool-season crops should be stored at cooler temperatures (32 to 35�F), and warm-season crops should be stored at warmer temperatures (45 to 55�F). There are exceptions to this rule, though. Table 1 lists optimum storage temperatures for commonly grown Kansas fruits and vegetables.

Freezing Injury. Temperatures that are too low can be just as damaging as those too high. Freezing will occur in all commodities below 32�F. Whether injury occurs depends on the commodity. Some can be repeatedly frozen and thawed without damage, while others are ruined by one freezing. Table 1 shows the highest freezing point for most fruits and vegetables. Table 3 lists susceptibility to freezing injury. Produce that is likely to be injured by one freezing is classified as "most susceptible." The "moderately susceptible" produce will recover from one or two freezings. Produce which is "least susceptible" can survive several freezings without injury.

Injury from freezing temperatures can appear in plant tissues as loss of rigidity, softening and water soaking. Injury can be reduced if the produce is allowed to warm up slowly to optimum storage temperatures, and if it is not handled during the thawing period. Injured produce should be marketed immediately, as freezing shortens its storage life.

Chilling Injury. Fruits and vegetables that require warmer storage temperatures (40 to 55�F) can be damaged if they are subjected to near freezing temperatures (32�F). Cooler temperatures interfere with normal metabolic processes. Injury symptoms are varied and often do not develop until the produce has been returned to warmer temperatures for several days. Besides physical damage, chilled produce is often more susceptible to disease infection. Table 4 lists susceptible fruits and vegetables, and characteristic symptoms of chilling injury.

Back to top

Storage Facilities

Crops that require different storage conditions will need three different storage facilities.

Cold storage (temperatures 32 to 36�F).

Cool storage (temperatures 40 to 55�F).

Warmer storage (temperatures 55 to 60�F for sweet potatoes, squash, pumpkins or similar crops).

A recording thermometer can be helpful in determining whether storage facilities are maintaining ideal conditions and are not fluctuating. A maximum/minimum thermometer could be substituted. The thermometer should not be the same as the thermostat controlling the refrigeration equipment. Relative humidity also should be monitored with a hygrometer or a sling psychrometer.

Controlling and monitoring temperature and relative humidity will enable a grower to maintain optimum conditions for maximum storage life of the crop, and to minimize crop damage from chilling, freezing and/or too-high temperatures and water loss from the crop. Close attention to storage conditions will yield returns through greater customer satisfaction, less waste and spoilage, and in the flexibility to hold a crop without significant storage losses to wait for better markets.

References

Hardenburg, R.E., A.E. Watada and C.Y. Wang. 1986. The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Stocks. USDA-ARS Agriculture Handbook Number 66 (revised) 136p.

Back to top

Table 1. Commonly grown fruits and vegetables with recommended storage conditions for temperature and relative humidity  approximate storage life under optimum conditions and highest freezing points.

Commodity

Temperature (�F)

Rel. humidity (percent)

Approximate storage life

Freezing point (�F)

FRUITS

Apples

 30�40

 90�95

 1�12 months

 29.3

Apricots

 31�32

 90�95

 1�3 weeks

 30.1

Berries

Blackberries

 31�32

 90�95

 2�3 days

 30.5

Currants

 31�32

 90�95

 1�4 weeks

 30.2

Elderberries

 31�32

 90�95

 1�2 weeks

 �

Gooseberries

 31�32

 90�95

 3�4 weeks

 30.0

Raspberries

 31�32

 90�95

 2�3 days

 30.0

Strawberries

 32

 90�95

 3�7 days

 30.6

Cherries, sour

 32

 90�95

 3�7 days

 29.0

Cherries, sweet

 30�31

 90�95

 2�3 weeks

 28.8

Grapes, American

 31�32

 85

 2�8 weeks

 29.7

Nectarines

 31�32

 90�95

 2�4 weeks

 30.4

Peaches

 31�32

 90�95

 2�4 weeks

 30.3

Pears

 29�31

 90�95

 2�7 months

 29.2

Plums and prunes

 31�32

 90�95

 2�5 weeks

 30.5

Quinces

 31�32

 90

 2�3 months

 28.4

VEGETABLES

      Back to top

Artichokes, Jerusalem

 31�32

 90�95

 4�5 months

 28.0

Asparagus

 32�35

 95�100

 2�3 weeks

 30.9

Beans, dry

 40�50

 40�50

 6�10 months

 �

Beans green or snap

 40�45

 95

 7�10 days

 30.7

Beans, lima

 37�41

 95

 5�7 days

 31.0

Beans, sprouts

 32

 95�100

 7�9 days

 �

Beets, bunched

 32

 98�100

 10�14 days

 31.3

Beets, topped

 32

 98�100

 4�6 months

 30.3

Broccoli

 32

 95�100

 10�14 days

 30.9

Brussels, sprouts

 32

 95�100

 3�5 weeks

 30.5

Cabbage, early

 32

 98�100

 3�6 weeks

 30.4

Cabbage, late

 32

 98�100

 5�6 months

 30.4

Cabbage, Chinese

 32

 95�100

 2�3 months

 �

Carrots, bunched

 32

 95�100

 2 weeks

 �

Carrots, mature

 32

 98�100

 7�9 months

 29.5

Carrots, immature

 32 

 98�100

 4�6 weeks 

29.5

Cauliflower

 32

 95�98

 3�4 weeks

 30.6

Celeriac

 32

 97�99

 6�8 months

 30.3

Celery

 32

 98�100

 2�3 months

 31.1

Chard

 32

 95�100

 10�14 days

 �

Chicory, witloof

 32

 95�100

 2�4 weeks

 �

Collards

 32

 95�100

 10�14 days

 30.6

Corn, sweet

 32

 95�98

 5�8 days

 30.9

Cucumbers

 50�55

 95

 10�14 days

 31.1

Eggplant

 46�54

 90�95

 1 week

 30.6

Endive and escarole

 32

 95�100

 2�3 weeks

 31.9

Garlic

 32

 65�70

 6�7 months

 30.5

Greens, leafy

 32

 95�100

 10�14 days

 �

Horseradish

 30�32

 98�100

 10�12 months

 28.7

Jicama

 55�65

 65�70

 1�2 months

 �

Kale

 32

 95�100

 2�3 weeks

 31.1

Kohlrabi

 32

 98�100

 2�3 months

 30.2

Leeks

 32

 95�100

 2�3 months

 30.7

Lettuce

 32

 98�100

 2�3 weeks

 31.7

Melons

      Back to top

Cantaloupe (3/4 slip)

 36�41

 95

 15 days

 29.9

Cantaloupe (full slip)

 32�36

 95

 5�14 days

 29.9

Casaba

 50

 90�95

 3 weeks

 30.1

Crenshaw

 45

 90�95

 2 weeks

 30.1

Honey Dew

 45

 90�95

 3 weeks

 30.3

Persian

 45

 90�95

 2 weeks

 30.5

Watermelon

 50�60

 90

 2�3 weeks

 31.3

Mushrooms

 32

 95

 3�4 days

 30.4

Okra

 45�50

 90�95

 7�10 days

 28.7

Onions, green

 32

 95�100

 3�4 weeks

 30.4

Onion, dry

 32

 65�70

 1�8 months

 30.6

Onion sets

 32

 65�70

 6�8 months

 30.6

Parsley

 32

 95�100

 2�2.5 months

 30.0

Parsnips

 32

 98�100

 4�6 months

 30.4

Peas, green

 32

 95�98

 1�2 weeks

 30.9

Peas, southern

 40�41

 95

 6�8 days

 �

Peppers, chili (dry)

 32�50

 60�70

 6 months

 �

Peppers, sweet

 45�55

 90�95

 2�3 weeks

 30.7

Potatoes, early crop

 40

 90�95

 4�5 months

 30.9

Potatoes, late crop

 38�40

 90�95

 5�10 months

 30.9

Pumpkins

 50�55

 50�70

 2�3 months

 30.5

Radishes, spring

 32

 95�100

 3�4 weeks

 30.7

Radishes, winter

 32

 95�100

 2�4 months

 �

Rhubarb

 32

 95�100

 2�4 weeks

 30.3

Rutabagas

 32

 98�100

 4�6 months

 30.0

Salsify

 32

 95�98

 2�4 months

 30.0

Spinach

 32

 95�100

 10�14 days

 31.5

Squashes, summer

 41�50

 95

 1�2 weeks

 31.1

Squashes, winter

 50

 50�70

 1�6 months

 30.5

Sweet potatoes

 55�60

 85�90

 4�7 months

 29.7

Tomatoes mature�green

 55�70

 90�95

 1�3 weeks

 31.0

Tomatoes firm�ripe

 55�70

 90�95

 4�7 days

 31.1

Turnips

 32

 95

 4�5 months

 30.1

Turnip greens

 32

 95�100

 10�14 days

 31.7

Watercress

 32

 95�100

 2�3 weeks

 31.4

Back to top

Table 2. Fruits and vegetables classified by their respiration rates (at 41�F).

Class

Respiration rate Btu/ton/24 hrs

Commodity

Very low

 <5

Nuts, Dates, Dried Fruits and Vegetables

Low

 5�10

Apple, Grape, Garlic, Onion, Potato (mature), Sweet Potato 

Moderate

 10�20

Apricot, Cherry, Peach, Pear, Nectarine, Plum, Cabbage, Carrot, Lettuce, Pepper, Tomato, Potato (immature)

High

 20�40

Strawberry, Blackberry, Lima Bean, Raspberry, Cauliflower

Very high

 40�60

Artichoke, Snap Bean, Green Onion, Brussels Sprouts

Extremely high

 >60

Asparagus, Broccoli, Sweet Corn, Mushroom, Spinach, Pea

Back to top

Table 3. Fruits and vegetables classified by susceptibility to injury by temperatures below 32F.

Group 1 
Most susceptible   

Group 2 
Moderately  susceptible   

Group 3 
Least susceptible

Apricots   

 Apples   

 Beets1

Asparagus   

 Broccoli, sprouting   

 Brussels Sprouts

Beans, snap   

 Cabbage, new   

Cabbage, mature and savoy

Berries (except cranberries)   

 Carrots  

 Kale

Cucumbers   

 Cauliflower   

 Kohlrabi

Eggplant   

 Celery   

 Parsnips

Lettuce   

 Cranberries   

 Rutabagas

Okra   

 Grapes   

 Salsify

Peaches   

 Onions (dry)   

 Turnips1

Peppers, sweet   

 Parsley

Plums   

 Pears

Potatoes   

 Peas

Squash, summer   

 Radishes1

Sweet Potatoes   

 Spinach

Tomatoes   

 Squash, winter

1Without tops


Back to top

Table 4. Fruits and vegetables susceptible to chilling injury when exposed to temperatures below their optimum range and above 32�F.

Commodity   

Approx. lowest safe temperature (�F)   

Symptoms of injury from below-optimum temperatures

Apples-certain cultivars   

 36�38   

Internal browning, brown core, soggy breakdown, soft scald

Asparagus   

 32�36   

Dull, gray-green, limp tips

Beans (lima)   

 34�40   

Rusty brown specks, spots, or areas

Beans (snap)   

 45   

Pitting and russeting

Cucumbers   

 45   

Pitting, water-soaked spots, decay

Eggplants   

 45   

Surface scald, alternaria rot, blackening of seeds

Melons

     Cantaloupe   

 36�41   

Pitting, surface decay

     Honey Dew 

45�50 

 Reddish-tan discoloration, pitting, surface decay, failure to ripen

     Casaba   

 45�50   

Same as above, but no discoloration

     Crenshaw and  
     Persian   

 45�50   

Same as above, but no discoloration

     Watermelons   

 40   

Pitting, objectionable flavor

Okra   

 45   

Discoloration, water-soaked areas, pitting, decay

Peppers, sweet   

 

 45   

Sheet pitting, alternaria rot on pods and calyxes, darkening of seed

Potatoes   

 38   

Sweetening

Pumpkins and hardshell squashes   

50   

Decay, especially alternaria rot

Sweet Potatoes   

 

 55   

Decay, pitting, internal discoloration; hard core when cooked

Tomatoes

     Ripe   

 45�50   

Water soaking and softening decay

     Mature-green   

 55   

Poor color when ripe, alternaria rot

Back to top


For more information, contact your University of Maine Cooperative Extension county office.

Published and distributed in furtherance of Acts of Congress of May 8 and June 30, 1914, by the University of Maine Cooperative Extension, the Land Grant University of the state of Maine and the U.S. Department of Agriculture cooperating. Cooperative Extension and other agencies of the U.S.D.A. provide equal opportunities in programs and employment.


Return to Publications Catalog Online Table of Contents
Return to Publications Homepage


Putting knowledge to work with the people of Maine

The University of Maine Cooperative Extension logo

A Member of the University of Maine System
Last Modified: 08/12/08
These pages are currently being maintained from the
Communications Office, University of Maine Cooperative Extension.
Send comments, suggestions or inquiries to www-questions@umext.maine.edu
  


COUNTY OFFICES | PROGRAMS | RESOURCES | PUBLICATIONS | NEWS AND EVENTS | UMAINE EXTENSION HOME  | UMAINE

 

 

This is the National Ag Risk Education Library's cache of http://www.umext.maine.edu/onlinepubs/htmpubs/4135.htm as retrieved on 11/5/2008.

The document may have changed since this page was created. Click here for the current page.



National Ag Risk Education Library is not affiliated with the authors of this page nor responsible for its content.