Leftover raw egg whites can be kept in the refrigerator for up to 4 days. If you don't believe you'll need them in 4 days, they may also be frozen! Just add egg whites to ice cube trays and freeze until solid. Remove them from the tray and place the frozen cubes into a freezer bag for later use. Freezing egg whites is a fantastic way to preserve them without trying to beat the four-day expiration date if left in the refrigerator.