Dehydrated and frozen egg whites are cheaper and more efficient than fresh egg whites. However, each lot of dehydrated egg whites varies from the next. This results in each batch of cakes varying in texture, moisture, volume, and height. Surfactants that have been used to improve the whipping properties of dehydrated eggs are sodium desoxycholate, triethyl citrate, triacetin, sodium oleate and oleic acid. Frozen egg whites do not form as firm or stable foams as fresh egg whites. It may be necessary to adjust the pH if the eggs have been refrigerated for a long time because they become more alkaline than fresh eggs. Acids can be added in manufacturing such as acetic, malic, tartaric, and citric. These improve the color and cake structure by lowering the pH, however they do not work as well as cream of tartar.