Cheese

Shalom!

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The sages banned cheese made by Gentiles, even if all the ingredients are kosher, out of concern that the cheese might be produced with non-kosher animal rennet.

In past times, rennet was used to make cheese as it is an enzyme that coagulates cheese by causing the water content to separate from the milk content. Rennet is an animal product that is not only meat but derives from non-kosher animals. So too, even though the amount of rennet used in cheese production is usually less that one-sixtieth, and such minute amounts are generally ignored, the rennet cannot be ignored because it is a “davar hama’amid” – an ingredient that causes significant change which cannot be nullified.

Even though animal rennet is rarely used in the common mass-produced cheese you find in your supermarkets, and other cheese binding agents are used, the ban on using cheese made by Gentiles applies even if all the ingredients are otherwise kosher. Cheese is a unique product that must have kosher certification even though the ingredients all appear to be kosher.

SOURCES: YD 115 and commentaries