A Staff Report from the Straight Dope Science Advisory Board

Is rennet, a cheese ingredient, made from calves' stomachs?

May 8, 2000

Dear Straight Dope:

As you were able to alleviate my friend Jennifer's ignorance regarding baby-naming laws, I thought you might be able to help me with another question about infant mammals. Is it true that adorable and harmless calves are killed to get the rennet needed to make cheese? I've always abstained from eating veal because it felt sort of wrong to eat a baby anything. Should I now give up cheesecake, pizza, and Kraft singles on this principle? Please help me with this moral dilemma!

SDStaff Jillgat replies:

My co-worker Joanne used to be an ovo-lacto vegetarian — she consumed eggs and dairy products but not meat — until one day while driving past a dairy on the way to work, she came to the conclusion that being a meat cow wasn't as bad as it gets. At least they didn't have to live as long in such appalling conditions as dairy cows and chickens do. Now she's a "vegan" vegetarian, which means she's no fun to go out to lunch with. "Enchiladas, hold the cheese"? Puh-leeze. But I see her point.

The cheesemaking process varies some with the type of cheese, but all basically use the same method. Milk is heated (pasteurized) to destroy harmful bacteria, then cooled and a starter culture of bacteria that produces lactic acid is added to start the coagulation process. Next, for most types of cheese, rennet is added to speed the coagulation and separate the milk into solid curds and liquid whey. The whey is drained off, the curd is heated and/or pressed and it's molded and shaped into a cheese. Some are then "matured" or aged.

Rennet contains an enzyme called chymosin that is traditionally obtained from the "abomasum" (fourth stomach) of a newborn calf or lamb. Adult mammals don't have this enzyme — newborn calves and lambs need it to help digest and absorb milk. Almost all European cheeses still use animal rennet. Vegetarian rennet has been obtained from fig leaves, melon, safflower and wild thistle, but most commercially available non-animal rennet is now produced in laboratories from fungal or bacterial sources (not sure if they use baby fungi and bacteria or not), and works like the animal-based product.

Genetic engineering techniques are also now used to extract the DNA which encodes for chymosin from calf stomach cells, introducing it into a micro-organism which grows the chymosin in commercial quantities. This product is identical to that produced by newborn calves and, according to the Vegetarian Society of the United Kingdom (https://www.vegsoc.org/cheese), "Its manufacturers say that genetically engineered chymosin will end the cheese making industry's reliance on the slaughter of calves." Of course there are those who are opposed to genetic engineering of any kind, so they'll want to stick with the non-animal based rennet.

If you're lucky enough to live near a "Trader Joe's" store, you will find cheeses categorized into three rennet categories: animal, vegetable, and microbial.

I know your heart goes out to baby calves, but one thing can be said for the cattle industry. Very little of the slaughtered animal goes to waste. A pet store in my town has a bin full of "bull chews" you can buy for your dog. I'm not sure how many customers realize they're purchasing dried bull penises.

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