casein, the principal milk protein, is used by winemakers as a fining agent particularly useful for removing brown colours from white wines. It is also used to a lesser extent in the general clarification of young wines. Precipitated from milk by the addition of acids, casein is chiefly used in the form of sodium or potassium caseinate. When this salt is added to cloudy wine, it reacts with some of the wine acid forming a curd which adsorbs and precipitates most of the very small particles, including the pigments causing discoloration. In many countries, the use of casein must be declared on the label. See labelling information.