What is Curing of Onion
February 1, 2019
Curing of Onion
- Onions should be adequately cured in the field, in open sheds, or by artificial means before or in storage. Adequate curing in the field or in open sheds may require 2 to 4 weeks, depending on the weather.
- The best skin color develops at 75 to 90° F. The most common method of curing in northern areas is by forced ventilation in the storage by blowing heated air at 75 to 85° F, through the bottom of the onion pile to the top, at two to three cubic feet of air per minute for each cubic foot of onions (or 30-50cfm/ton).
- Use the higher airflow rate initially to remove surface moisture and seal necks. If the weather is cool and wet, forced air at 75 to 85° F and 70% relative humidity is recommended.
- If the onions are also wet, forced air at 85° F and a relative humidity of 25-35%. Relative humidity should be used as soon as storage loading is completed. This should be continued until the outer skins and neck are dry.
- Onions are considered cured when the neck is tight and the outer scales are dry and make a rustling sound when handled.
- This condition is reached when onions have lost 3 to 5 % of their weight. If not adequately cured, onions are likely to decay in storage.
- The common form of decay is gray mold rot (Botrytis), which occurs at the top of the bulb hence its name “neck rot”.
- High temperatures and high humidity (80%) during curing with good air circulation favor development of desirable skin color.
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