Vegetable storage for extended marketing

Collin Thompson, Michigan State University Extension - November 13, 2017

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

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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