Curing
The only post-harvest treatment required for the long storage of bulb onions is a thorough curing of the bulbs. Curing is a drying process intended to dry off the necks and outer scale leaves of the bulbs to prevent the loss of moisture and the attack by decay during storage. The essentials for curing are heat and good ventilation, preferably with low humidity. This dries out the neck and the two or three outer layers of the bulb. The outermost layer, which may be contaminated with soil, usually falls away easily when the bulbs are cured, exposing the dry under-layer, which should have an attractive appearance. Onions are considered cured when neck is tight and the outerscales are dried until they rustle. This condition is reached when onions have lost 3 to 5% of their weight.
If onions cannot be dried in the field, they can be collected in trays, which are then stacked in a warm, covered area with good ventilation.
In cool, damp climates, onions in bulk ventilated stores are dried with artificial heat blown through the bulk at a duct temperature of 30 degrees Celsius.
Onions can also be cured by tying the tops of the bulbs in bunches and hanging them on a horizontal pole in a well-ventilated shades. Curing in shade improves bulb colour and reduces losses significantly during storage
Grading
Onions after curing are graded manually before they go in to storage or for marketing. The thick neck, bolted, doubles, injured and decayed bulbs are picked out so also misshapen small bulbs. Sorting and grading is done after storage also to fetch better price. The outer dry scales usually rub off during the grading process, giving the onions a better appearance for market. It has been experienced that if storage is arranged after proper sorting and grading losses in storage are reduced.
For local market the onions are graded based on their size.
Extra large onion (>6 cm dia.)
Medium (4-6 cm dia.)
Small (2-4 cm dia.)
The extra large onions have great demand and fetches very good price.
General Characteristics
The bulbs shall: