Clearly seltzer adds refreshing fizz to cranberry juice or sangría. But its colorless, odorless, tasteless bubbliness also makes it the ideal secret ingredient to lighten up foods. Think batters and soups. (Thanks, air pockets!) Seltzer and club soda can be used interchangeably, but steer clear of sparkling water, which doesn’t have enough carbonation to leaven. And be sure to use a bottle that’s fresh from the store; over time seltzer goes flat.