Cholov Yisroel

Cholov yisroel (Hebrew: חלב ישראל) refers to all dairy products, including cheese and non-fat dry milk powder, which have been under the supervision of a Jew.

Under Jewish halachic law, milk is kosher only if it comes from a kosher species of animal (such as cows, goats, and sheep), but milk from a non-kosher species (such as horses, pigs, and camels) is forbidden.

In the past it was not uncommon for farmers to mix the milk of their various herds together, unbeknownst to their customers. Since it was conceivable to have a farm selling a mixture of Kosher and non-Kosher milk, Rabbis issued an injunction against the use of milk from a non-Jewish farmer; such milk is referred to as cholov akum. The restriction did not apply if there was supervision of the milking process by a Jew until the milk was sold. The milk itself is automatically kosher (so long as it is 100% from a kosher animal, namely, a cow, sheep, goat, or other kosher mammal) but the Rabbis' decree served to protect people from potential dairy deception.

In the USA
Nowadays, modern health standards (regulated by Health and Food standards organizations, such as the FDA) are intended to make sure that cow's milk sold in stores is 100% cow's milk. Therefore, many prominent Orthodox rabbinical authorities, all basing their subsequent decisions on the ruling of Rav Moshe Feinstein, permit the use of regular cows' milk in the United States. This is sometimes referred to as cholov stam. On the other hand, many prominent Orthodox Rabbis actually forbid the use of milk that is not cholov yisroel under any circumstance as violation of a rabbinical prohibition.

Many Jews who wish to strive for a stricter observance of Jewish law only consume dairy products that are supervised by a mashgiach and are certified with the label: "Cholov Yisroel". The retention of the Cholov Yisroel system is also related to the retention of traditions/customs, a central part of Judaism. There are also kabalistic reasons for being strict concerning cholov yisroel, which go beyond as to whether or not there is a possibility of mixing non-kosher milk.