Because Sweet Onions sometimes sell out quickly, it's a good idea to stock up when you can. Here are some simple tips for buying and storing "sweets".
Look for sweet onions that light golden-brown in color, with a shiny tissue-thin skin and firm, tight, dry necks. (Ordinary storage onions are darker and have a thicker skin.) When cut into, sweet onions should have a creamy white interior. Avoid onions that have soft spots or surface bruises.
Because sweet onions are high in water and sugar content they require more care when storing, so treat them gently to avoid bruising. Store away from potatoes because they'll absorb water. Generally, sweet onions will keep for 4-6 weeks or longer. Cut onions should be wrapped tightly in plastic wrap and refrigerated - The favorite way to store "sweets".
In the refrigerator: Store in a single layer in the vegetable bin on paper towels. Or, for longer storage, wrap in foil.
In pantyhose: Take a leg from a pair of clean, sheer pantyhose, drop and onion into the foot, tie a knot and repeat as necessary. Hang in a cool, dry, well-ventilated area. Cut above the knt when ready to use.
On racks or screens: Place on elevated racks or screens, not touching, in a cool area.
In the freezer: For long-term storage, sweet onions can be frozen, but their texture changes so they should be used only for cooking. Chop and place on a cookie sheet and place in the freezer. When frozen, store in freezer containers or bags. To store whole onions, peel wash, core and freeze in a freezer-proof container or bag.
Drying: Chop and dry in the oven, using the lowest setting. Remove when thoroughly dry but not brown. Store at room temperature in airtight containers.