By Collin Thompson
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.
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 |
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 |