Batters are semiliquid mixtures containing flour or other starch. They are used in deep-frying to give a crisp, flavorful, golden brown coating. There are many formulas and variations for batters:
Many liquids are used, including milk, water, and beer.
Eggs may or may not be used.
Thicker batters make thicker coatings. Too thick a batter makes a heavy, unpalatable coating.
Leavenings are frequently used to give a lighter product. These may be:
Baking powder
Beaten egg whites
Carbonation from beer or seltzer used in the batter