Onion - Postharvest Care
Onions stored in bags can be stacked on crates.
Onions are typically stored in bags, crates, bulk bins, or pallet boxes that hold about a half ton of loose onions. Bags of onions should be stored on pallets and stacked to allow proper air circulation. Air-cooled storage facilities use forced ventilation systems in which air, heated if necessary, is introduced through floor racks beneath the onions. Bulk onions are stored on the floor up to 10 feet deep. When piles are too deep, onions near the bottom exhibit significant compression injury. Bulk floor storage should have air pipes running through the bottom of the pile or have holes and pipes in the concrete floor for ventilation. Bin-stored onions can be as high as 25 feet with air blown through the boxes from the head wall.
Onions can be stored in either common or cold storage. The storage quality of onions is influenced by cultivar and by the conditions under which they are grown, harvested, cured, and stored. Onions to be held in cold storage should be placed there immediately after curing. A temperature of 32°F will keep onions dormant and reasonably free from decay, provided the onions were disease-free and well-cured when placed in storage. Onions will sprout and decay rapidly when stored at temperatures between 40 and 50°F. Sprout growth indicates a high storage temperature, poorly cured bulbs, or storage of immature bulbs. Root growth indicates that relative humidity in the storage facility is too high. Onions that freeze in the field need to be allowed to completely thaw out before handling. Onions that are damaged by freezing will have watersoaked scales when the thawed onions are cut.
Grading and Packaging
Onions are graded according to size and quality. A high-quality pack is obtained by eliminating immature, decayed, sunburned, mechanically injured bulbs, double bulbs, and bulbs with secondary growth. Bulbs are sorted, cleaned, sized and graded, just prior to bagging. They are packaged in 50-lb sacks or in consumer packs of 2, 5, and 25-lb mesh sacks.
Fresh market options for Utah-grown onions include wholesale markets, farmers’ markets, community supported agriculture (CSA) shares, restaurants, and roadside stands. Sales to local retail markets, such as supermarkets, are also an option. Buyers usually specify minimum sizes of the onions they will purchase. This minimum is usually two inches in diameter, with bulbs greater than three inches bringing a much higher price.