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Proper Storage Maintains Quality of Harvested Crops

Published: Friday, January 12, 2018

The following is from Collin Thompson, Michigan State University Extension educator.

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, resulting 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 is a list that details the relative respiration rates of various fruits and vegetables:

• 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—As-paragus, mushroom, parsley, peas, spinach, sweet corn

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.

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 list be-low:

• Cold and Very Moist (32-40° and 90-95 percent 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 percent RH)—Potatoes, cabbage, cauliflower, apples, grapes, pears, chicories

• Cool and Moist (40-50° and 85-90 percent RH)—Cucumbers, peppers, cantaloupe, watermelon, eggplant, tomatoes

• Cool and Dry (32-50° and 60-70 percent RH)—Garlic, onions

• Warm and Dry (50-60° and 60-70 percent RH)—Pumpkins, winter squash, sweet potatoes

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