Since it is not possible to distinguish kosher milk (from a kosher animal) from non kosher milk, Rabbinical law requires that it be supervised from the point of milking until it is bottled. In countries where the source of milk offered for sale is guaranteed by civil law (such as the UK), some authorities rule that all milk is guaranteed as kosher and need not be supervised. Supervised kosher milk (Chalav Yisrael) is widely available nowadays in the major centres of Jewish life.