Once onions have been dried and cured, they must be taken to a storage facility to begin the cooling process. For areas where autumn and winter temperatures in the morning average below 33° F (0.6° C), fans can be used to cool and store the onions, a practice called room cooling. Temperature inside the facility must be brought down gradually to avoid damage, spoilage, and possible dehydration of the onions. Humidity must be monitored to ensure that condensation does not develop in the onions, promoting sprouting and spoilage or disease organisms to develop. During freezing weather conditions, it is recommended to mix outside air with air inside the storage facility to prevent onion dehydration (Matson, 1985).
For areas with warmer winters (above 33°F for several weeks at a time), refrigeration may be needed to preserve onion freshness. While not as cost-effective as room cooling systems, refrigeration systems can be valuable when there is economic incentive to store the onions for later sale. See Cooling Techniques and Post-Harvest Recommendations for more information.