If you can smell onions in your refrigerator, you aren't storing them properly or your airtight container isn't really airtight. They're probably anointing other foods in your fridge, especially dairy products like cream and fats like butter, with their less-than-blessed aroma, too. Professional kitchens use a technique called "banquet wrapping" to keep the odor in their well-stocked walk-in coolers as neutral as possible, and you can use the same method to keep your onions fresh -- and their odor contained -- in your refrigerator at home.
Place the sliced onions in a plastic storage container. Wrap the entire container crosswise in two layers of plastic wrap; stretch the plastic wrap tightly to seal the container. Wrap the container again with two layers of plastic wrap, this time in the direction perpendicular to the first. Again, stretch the plastic over them tightly; store onions up to five days in the refrigerator.
Reviving the Onions
Revive limp sliced onions with ice water. Turgor pressure, the process that keeps plant cells plump with moisture, is responsible for an onion's limpness or firmness. If you have limp onions after storing them, submerge them in ice water for 5 to 10 minutes, then drain and pat them dry to restore their crispness.