Optimum
conditions for storing onions are 32°F and relative humidity of 65–70 %.
Keeping quality after December is directly dependent upon having the onion bulb
around 32ºF by mid-December. Under northern climate conditions, it is suggested
to aim for 70°F by the end of September, 50°F by the end of October, 40°F by
the end of November, and 32°F by mid-December. Onions will freeze at 31°F. The
effects of freezing are cumulative. That is, several short periods be-low 31°F
are just as damaging as a single longer period. Onions that have frozen become
soft and decay quickly. Onions that are held at temps above 50°F are subject to
sprouting.
Once
the holding temperature is reached, inside air should be re-circulated at least
twice a day to maintain a uniform storage condition. Airflow should be 0.25 to
0.5 cubic feet per minute (cfm) per cubic foot of product. Avoid condensation
from forming on the onions because it is favorable for sprouting, and disease
development and spread in storage: 1) Do not place cool onions in storage early
in the morning (storage air temp warmer than onions) and 2) Do not circulate
warm air over cold onions, open the storage doors when the air outside is cool
and dry to exhaust warm moist air. Remember, humid air contains more moisture
and will condensate at warmer temperatures than dryer air. Also, smaller bulbs
pack tighter and may need more air circulation.
Monitor
storage conditions. Check and test equipment and all controls frequently for
proper function during the storage season.
Source:
Veg Edge Weekly, Vol. 8 Issue 25
