Cheese and Gevinas Yisroel

People routinely assume that kosher milk makes kosher cheese. It does not. Cheese carries a second, independent requirement — gevinas yisroel — and it applies whatever the milk's status.

Where the requirement comes from

The Shulchan Aruch gives the reason: cheese made by a non-Jew was prohibited because rennet was taken from the stomach lining of a non-kosher animal.

The obvious modern question follows immediately — most cheese in many countries is now made with microbial or fermentation-produced rennet rather than animal rennet. Does the requirement lapse?

It does not. The requirement is not conditional on which rennet is actually used. There is a minority view that cheese of a non-Jew should be permitted where animal rennet is not used, but that is not how the halacha is held.

What a Jew has to do

For rennet-set cheese to be gevinas yisroel, a Jew must own the rennet or place it into the vat. In commercial practice that means adding it, or pressing the button on an automated rennet feeder.

Note how small the required involvement is — and how specific. It is not general supervision of the cheesemaking. It is that one act, at that one moment.

Which cheeses

The requirement covers the rennet-set cheeses — the hard cheeses. That includes cheddar, mozzarella, Swiss, parmesan, provolone, muenster, feta, blue and American.

Acid-set soft cheeses are made differently, by souring rather than by rennet, and whether the same rules apply to them is a real dispute among the poskim. This is why agencies differ on cream cheese and cottage cheese, and why it is worth asking rather than assuming in either direction.

Whey

Whey is the liquid drawn off when milk is coagulated, and it sits in its own discussion.

One position holds that whey is outside the decree entirely, since the enactment was on cheese and not on by-products — and on that view it would be permitted even from cheese that was not itself acceptable.

A stricter position holds that whey is permitted where non-kosher rennet was used only if the cheese it came from was not heated past a certain point, and the common practice follows that stricter view.

This matters far beyond cheese, because whey, whey protein and lactose appear in protein powders, bars, baked goods and a great deal else.

Butter

Butter is a further separate question. One line of reasoning holds that the decree on cheese was never extended to butter, since no curdling agent is involved and the concern about non-kosher rennet does not arise. Others are concerned about milk of another species being present. There are established grounds for stringency and established grounds for leniency, and practice varies.

Which of these your household follows is a question for your rav. See also cholov yisroel and cholov stam, which is the separate question about the milk itself.