No, cream of tartar isn’t a required ingredient, although this natural fruit acid by-product serves several purposes in a meringue. Cream of Tarter is a leavening agent, an egg white stabilizer, and keeps sugar from crystallizing. Use a 1:2 ratio of cream of tarter to lemon juice or white vinegar for light and airy foam. Without a stabilizing agent, meringue foam can release air bubbles, become watery, and collapse more quickly.