What is the best way to store sliced onions?
Old wives’ tales claim that storing sliced or chopped onions in water will help keep their pungency from intensifying, but we found the exact opposite to be the case. We stored sliced onions for two days submerged in water as well as placed directly in zipper-lock bags, and then compared their odor and flavor to freshly sliced onions. The onions submerged in water were unanimously deemed to be most odorous with the sharpest flavor. It turns out that over time, water facilitates the distribution of enzymes known as alliinases across the cut surfaces of the onion, which in turn leads to an increase in the creation of thiosulfinates that produce an onion’s pungent odor and flavor. (See “Taming Raw Onion Flavor" related.) Your best bet is to simply slice or chop onions as you need them, but if you find yourself with an excess, store them in the fridge in a zipper-lock bag and give them a quick rinse to remove any thiosulfinates on their surface right before using.