Vegetable storage for extended marketing

Whether holding items in storage throughout the main production season, or extending the marketing season into the winter, proper handling and storage techniques will help maintain quality of harvested crops.

Hydro-cooled carrots getting ready for winter storage. Properly handled carrots can last eight months in storage. | Photo by Collin Thompson

Hydro-cooled carrots getting ready for winter storage. Properly handled carrots can last eight months in storage. | Photo by Collin Thompson

Crop Respiration

When a crop is harvested, it begins the decay process through respiration. As growers, our task is to slow this decay by using proper post-harvest handling and storage techniques. This will allow for increased quality over a longer period of time, which translates to continued sales into the colder months of the year. Respiration is the process of breaking down carbohydrates in an attempt to keep the harvested plant tissue alive. Through this process, oxygen is absorbed, while heat, water and carbon dioxide is released, similar to human respiration. As respiration continues, the quality of the harvested crop degrades, result in the loss of flavor, turgor and nutritional value. Respiration occurs at different rates depending on the type of crop. Generally speaking, a higher respiration rate equates to a shorter shelf life, though there is variability among crop types. Below you will find a chart that details the relative respiration rates of various fruits and vegetables:

Respiration Rate

Commodity

Very Low

Dried fruits and vegetables, nuts

Low

Apple, beet, celery, cranberry, garlic, grapes, honeydew melon, onion, potato (mature), sweet potatoes, watermelon

Moderate

Apricot, blueberry, cabbage, cantaloupe, carrot (topped), celeriac, cherry, cucumber, gooseberry, lettuce (head), pear, pepper, plum, potato (immature), radish (topped), summer squash, tomato

High

Blackberry, carrot (with tops), cauliflower, leeks, lettuce (leaf), lima beans, radish (with tops), raspberry, strawberry

Very High

Artichoke, bean sprouts, broccoli, Brussels sprouts, endive, green onions, kale, okra, snap bean

Extremely High

Asparagus, mushroom, parsley, peas, spinach, sweet corn

Slama, Jim, and Atina Diffley. Wholesale Success. 2013. Family Farmed. Fourth Edition.

Harvest Quality

To maximize storage potential of a crop, it is important to harvest at the right time – at physiological maturity – before the natural decline in quality occurs. Careful handling of produce is equally important, as bruises or damaged tissues encourage rot and decay, reducing shelf life and storage quality. Below is a chart describing ideal characteristics at harvest for various fruits and vegetables:

Crop

Harvest Quality

Crop

Harvest Quality

Asparagus

Bracts at tips closed

Leeks

Size, crisp

Basil

Fresh, tender leaves

Lettuce

Compact head, crisp, tender

Beans, snap

Seeds developed, plump

Onion, bulb

Firm bulbs, tight necks

Beans, lima

Crisp pods, seeds immature

Onion, green

Crisp stalks, firm bulbs

Beets, bunched

Crisp, fresh leaves

Parsley

Crisp, dark green leaves

Beets, root

Firm, deep colored roots

Peas, in pods

Tender, green, sweet pods

Blackberries

Full color, sweet

Peppers

Firm, shiny, thick walls

Blueberries

Full color, sweet

Potatoes, early

Well shaped, defect free

Broccoli

Firm heads, buds not open

Potatoes, late

Well shaped, defect free

Brussels Sprouts

Firm sprouts

Pumpkins

Hard rind, good color, heavy

Cabbage

Crisp, firm, compact heads

Radishes

Firm, crisp, dark green leaves

Cantaloupe

Full slip, rind color

Raspberries

Full color, sweet

Carrots, topped

Tender, sweet roots

Rutabagas

Roots firm with smooth surface

Cauliflower

Compact, white curds

Spinach

Dark green, fresh crisp leaves

Celery

Crisp, tender

Squash, summer

Firm, shiny, proper size

Corn, sweet

Plump, tender kernels, dried silks

Squash, winter

Hard rind, heavy, good color

Cucumbers

Crisp, green, firm

Strawberries

Full color, sweet

Eggplant

Seeds immature, shiny, firm

Sweet Potatoes

Proper size, vines start to yellow, before frost

Endive

Fresh, crips, tender leaves

Tomatoes

Firm, uniform coloration

Garlic

5-7 green leaves with yellow tips

Turnips

Firm, heavy roots

Leafy Greens

Crisp, darkly colored leaves

Watermelon

Crisp, good flesh color, not mealy

Herbs

Fresh, crisp, tender leaves

 

 

Storage Conditions

Temperature and humidity during storage impact respiration rate, affecting the shelf life of a harvested product. In order to maximize storage potential of a harvested crop, it is important to bring the internal temperature of the harvest tissue to the ideal storage temperatures as quickly as possible. This can be done through air-cooling using refrigeration, or hydro-cooling using dunk tanks, flumes or other hydro-cooling technology. Optimum temperatures and humidity levels for various fruits and vegetables can be found in the chart below:

Cold and Very Moist

32-40° and 90-95% RH

Carrots, beets, parsnips, rutabagas, turnips, celery, Chinese cabbage, celeriac, winter radishes, kohlrabi, leeks, collards, broccoli, Brussels sprouts,

Cold and Moist

32-40° and 80-90% RH

Potatoes, cabbage, cauliflower, apples, grapes, pears, chicories

Cool and Moist

40-50° and 85-90% RH

Cucumbers, peppers, cantaloupe, watermelon, eggplant, tomatoes

Cool and Dry

32-50° and 60-70% RH

Garlic, onions

Warm and Dry

50-60° and 60-70% RH

Pumpkins, winter squash, sweet potatoes

Collin Thompson is the Farm Manager of The North Farm at the Michigan State University Upper Peninsula Research and Extension Center in Chatham, Michigan and a Community Food System Educator with MSU Extension.  

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