What is Curing of Onion

Table of Contents

Curing of Onion

  1. 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.
  2. 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).
  3. 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.
  4. 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.
  5. Onions are considered cured when the neck is tight and the outer scales are dry and make a rustling  sound when handled.
  6. 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.
  7. The common form of decay is gray mold rot (Botrytis), which occurs at the top of the bulb ­ hence its  name “neck rot”.
  8. High temperatures and high humidity (80%) during curing with good air circulation favor development  of desirable skin color.

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