Dairy salt is a culinary salt (sodium chloride) product used in the preparation of butter and cheese products that serves to add flavor and act as a food preservative. Dairy salt can vary in terms of quality and purity, with purer varieties being the most desirable for use in foods. Dairy salt has been used since at least the 1890s in England and the United States. In butter preparation, it serves to retain moisture, while in cheeses, it tends to reduce water content and slow the ripening process.