Cholov Yisroel and Cholov Stam

Cholov yisroel is milk whose milking was watched from start to finish by an observant Jew. Cholov stam is ordinary commercial milk. Both are sold as kosher; which you use is one of the clearest dividing lines in kosher practice, and it rests on a dispute worth actually understanding.

What the decree guards against

The Shulchan Aruch rules that milk produced without a Jew watching is forbidden. The prohibition is a rabbinic decree, and its purpose is narrow and specific: to prevent milk from a non-kosher species being mixed into what would otherwise be assumed to be cow's milk.

That is the whole of it. It is not about cleanliness, animal welfare or feed. It is a species guarantee, enforced by observation — a camel or a horse gives milk too, and without someone watching you have only the producer's word.

Rav Moshe Feinstein's heter

The reason ordinary milk is sold as kosher at all traces to a well-known ruling in Igros Moshe. The argument is that government regulation does the evidentiary work a human observer would do: adulterating milk carries real legal consequence, the facts are established and publicly known, and so we are all in effect witnesses to them — the principle of anan sahadei. On that basis, inspected commercial milk has the status of milk that was watched.

A follow-up question in the same volume raises the obvious objection: plants are inspected, but the milk comes from farms, and farms in his day frequently were not. The answer given is that the decree attaches at the point milk reaches the Jew's hand, not at every earlier stage — so what matters is the supervised plant.

Why it is disputed

This should be said plainly rather than glossed. The heter is not universally accepted. Chelkas Yaakov rejects it, and the Aruch HaShulchan appears to reject the very idea. Large communities never accepted it, and the number of people keeping cholov yisroel exclusively has grown rather than shrunk.

Someone who keeps cholov yisroel is not being stringent beyond the law. They are following a position that has always had substantial authority behind it.

What changed since

The factual ground the heter stood on has moved, and the honest account of where it stands today is interesting.

Modern plant inspection tests for bacteria and antibiotic residue. It does not test which species the milk came from, and inspectors no longer see the animals, because plants no longer sit beside their own herds. On its face that weakens the original argument considerably.

The contemporary answer is that the evidentiary weight has shifted from the plant to the farm. Farms are inspected several times a year; the standard inspection form carries an explicit provision that only cows are in the milking parlour; goat and sheep dairies require their own licensing; farms with other animals must house or partition them separately; and farm milk is laboratory-tested for protein, fat and cell counts — figures that differ by species, such that a single pail of another species in a silo sample would show in the result.

On that basis the heter is held to stand for those who rely on it. Note what this means: the modern reasoning is close to the inverse of the original, with farm inspection now carrying the argument and plant inspection secondary.

What it does not cover

Cholov yisroel is about the milk. It does not answer the separate question of cheese, which carries its own requirement — see cheese and gevinas yisroel. Whey and dairy derivatives are a further question again.

Which standard your household keeps is a matter of your community's practice and your rav's direction.