In an age where a substance intended for use as butter is in reality made of whale oil and one intended to substitute for egg whites is made from chemically treated animal blood, it is refreshing to know that there is still one entire family of foods being manufactured today by a method which has remained virtually unchanged for centuries. This genre of edibles is renowned for its nutritional and gastronomic virtues, and all connoisseurs of good food have their favorites among its varied types: cheeses. 

These all-natural delectables are not, however, without their halachic problems, as we shall see. The kosher consumer should not be led to assume that natural, old-fashioned foods are necessarily kosher. After all, even whale oil is quite natural and old-fashioned. 

All of the many varieties of commercially prepared cheeses available to today’s consumer are produced by the same basic process, an ancient and efficient one. A type of bacteria, known in the cheese trade as a “starter,” is added to a quantity of milk, souring the milk. In chemist’s terms, the lactose in the milk turns to lactic acid. Next, a curdling agent is added, and this coagulates part of the milk coming out a watery liquid known as whey. Whereas this mixture may be sufficiently processed for the likes of Miss Muffet, cheese afficionados prefer the results which come when the whey is drawn off and the curds are treated in a variety of fashions, resulting in a variety of cheeses. 

The second step in the above process, the addition of the curdling agent, is where the kashrus question arises. 

The most common curdling agent, known as rennet, generally comes from animal sources, specifically the lining of the stomachs of calves. Such an exotic ingredient is necessary because the enzymes therein are the only chemicals known to efficiently and effectively curdle milk. It seems that long ago, people realized this fact when they saw recently suckled milk curdling in the stomach of a just slaughtered calf and they experimented with scrapings of the stomach lining. 

Anthropology aside, the fact that there are kashrus implications in the use of rennet is obvious. 

If the source of rennet is a kosher species of animal, ritually slaughtered under rabbinical supervision, it may be used to turn milk into cheese. For rather involved halachic reasons, there is no problem of meat and milk mixing in such usage. Likewise, if rennet is extracted, as it occasionally is, from vegetable sources, there is no question as to the kashrus of the cheese when it is produced under rabbinical supervision. 

However, most commercial cheeses (except those produced under rabbinical supervision) are made with rennet derived from animals slaughtered by conventional non-kosher means. 

Even though there is a kashrus principle which generally allows minuscule quantitites of non-kosher ingredients to be, at least after the fact, legally overwhelmed by great quantities of kosher ingredients and rendered nonexistent, this principle cannot, unfortunately, be applied in the case of rennet. This is because rennet has an unmistakable coagulant effect on milk; where one substance visibly solidifies another, the solidifying agent is always considered a substantial factor, whatever its amount. 

An additional factor in prohibiting standard commercial cheeses, even when produced by using microbial agents for curdling as a substitute for rennet, is the existence of an ancient decree banning the use of cheeses produced by non-Jews. 

It would seem, up to this point, that the wonderful world of cheese would have to be added to the other delights which observant Jews forego to meet G-d’s standards for them. 

But, where there’s a will, of course, there’s a “whey.” 

As a response to the kashrus problems of cheese-making, several kosher cheese companies make use of rennet derived from exclusively kosher sources. Cheeses produced in this way are of the same quality and boast the same variety as their non-kosher counterparts. There is a good reason for this: the kosher cheese market at present cannot support the considerable outlay of capital required to purchase both the cheese-producing machinery and the expertise of giant non-kosher cheese companies. Therefore, special kosher runs are done at the standard cheese companies. A kashrus supervisor kashers any equipment requiring it, and sees to it that the next run of cheeses is produced using only kosher rennet. The rest is done by routine techniques, under rabbinical supervision, which gives the cheese the status of “Jewish-produced.” 

Observant cheese lovers are therefore not deprived of their high-quality delicacy. The rental of time and machinery and the cost of reliable supervision makes kosher cheese a bit more expensive than non-kosher, but the deal is certainly a bargain! 

NOTE: The general prohibition against all cheeses made by gentiles without supervision includes RENNETLESS CHEESE.

Therefore cheese requires supervision in all forms, including hard cheeses (such as American, Cheddar, Muenster, Swiss, etc.) and soft cheese (such as cottage, cream, farmer, and pot cheese).