Dairy Salt is a very finely ground, pure salt (with no starch, or iodine added) that can be an added ingredient when making butter and margarine.
Owing to the small size of its granules, it dissolves faster and better than other pure salts, which might be coarser.
In making butter at home, the ratio of dairy salt used was about 1 oz (30 g) per pound (450g) of butter.
The term “dairy salt” can also be used to mean rock salt fed to dairy herds.