The Food Lab: Better Home Cooking Through Science

whites that will hold their shape much better during
poaching or frying, as well as yolks that will remain better
centered when boiled. Because of the way their proteins
break down, eggs become looser and looser as they age.
There’s another important change too: as eggs age, they
become more and more alkaline. This is particularly
important in meringue-based dishes, as the pH of egg whites
can greatly affect their foaming power. Egg whites foam
best in slightly acidic environments, which means that old
eggs will produce looser, wetter foams. To counteract this, a
pinch of acidic cream of tartar will help your meringues stay
stiff and weep-free.