From Wikipedia:

Rennet /ˈrɛnɪt/ is a complex set of enzymes produced in the stomachs of ruminant mammals.

Every official-ish source I've seen (dictionary.com, Webster, Vergetarian Society, Wikipedia), more or less define vegetarianism as "doesn't eat meat... and sometimes avoids other animal products (e.g. milk & eggs)". Sometimes, like in the case of the Vegetarian society, to further define subsets like "Lacto-ovo-vegetarian".

A "complex set of enzymes" isn't meat but animal rennet is clearly derived from animals, so it would seem to me to be a clear case of "vegetarian but not vegan".

I've seen in some places people alternatively describe vegetarianism as "not using/eating things that entailed an animal's death" (although that would seem to preclude milk from being vegetarian), so I guess this might just be a case of varying definitions of vegetarianism, which is less interesting. But I've seen a lot of blogs, posts, etc. definitively declare that rennet is not vegetarian, so I feel like I'm missing something.

3 Answers 3


A few days ago I read this question on the Biology Stack Exchange

Does cheese contain cells of animal stomachs?

It reminds us how rennet is made:

Dried and cleaned stomachs of young calves are sliced into small pieces and then put into salt water or whey, together with some vinegar or wine to lower the pH of the solution. After some time (overnight or several days), the solution is filtered. The crude rennet that remains in the filtered solution can then be used to coagulate milk.

I think to key to the definition of vegetarianism that excludes rennet, and is, I think, the definition most widely used among vegetarians in my country (the UK), is in the first sentence.

I think that definition of a vegetarian is does not eat the substance of the body of a dead animal, or perhaps does not eat substances obtained as a direct result of the death of an animal.

Your question draws attention to the fact that other substances obtained from animals cause death:

I've seen in some places people alternatively describe vegetarianism as "not using/eating things that entailed an animal's death" (although that would seem to preclude milk from being vegetarian)

I assume that you are referring to the male calves of lactating mother cows who are killed because the dairy industry has no use for them. Male chicks are also killed at birth because there is no use for them in the egg industry.

We can see the difference between the two definitions. In the operative one that excludes rennet but not milk, we won't eat the dead body or its substances. We will not eat the dead themselves. This is true even if the substances themselves have been removed leaving only traces (thinking of non-vegetarian wine). In the one you proposed that [ought to] exclude[s] milk, we won't eat the substances whose production entails other deaths. We will not eat the substances produced only at the cost of death.

The smallness of this difference, the realization that eating the dead one barely differs from eating that which causes death, is one of the paths towards the practice of veganism, but to exclude rennet we don't need to travel that far. In the UK, cheese not made from animal rennet is labelled vegetarian, although some vegetarians here are not strict and eat any cheese and products containing cheese like basil pesto.

Other posts that discuss trace ingredients and challenge definitions and their boundaries:


Zanna's answer is very good but I would like to add a little.

There are no laws about what you may and may not eat to be allowed to call yourself vegetarian or vegan. You are free to pick your own definition and there are many variations.

When I was first vegetarian many years ago, some people took it to mean just "don't eat meat" and expected that I would eat fish and even chicken since it was common then for "meat" to mean what is now usually termed "red meat". The understanding has gradually improved over the years though more recently, people who eat fish and seafood but not other meat are becoming common and I know several who also eat chicken but not other meat. Some of these people call themselves "vegetarian" though usually when challenged they will admit "well not really".

Even ignoring these odd positions (*), there is a lot of variation in the interpretation of vegetarianism. At the strict end, they will check that their cheese did not use rennet and their beer or wine did not use finings. At the less strict end, they will just avoid things that are obviously bits of dead animals and will happily eat a dessert without worrying about whether it contained gelatine. A position that I have seen a lot is being strict (e.g. avoiding rennet) except for alcoholic drinks.

(*) Not so much odd positions but just odd if called vegetarian.

In some of my less strict phases, I would eat cheese with rennet. My defense was that it could have been made without but in a meat dominated economy there was no incentive for the manufacturers to avoid rennet. I used to have to go to a specialist shop and have very little choice to get rennet free cheese. This has improved over the years probably because there are now enough rennet avoiding vegetarians to affect the market. Rennet free cheese is now easy to obtain and there is plenty of choice.

Most people, even meat eaters, have limits as to what they will eat. E.g. cannibals are extremely rare. Fortunately, few people will eat other primates and I think that most would decline dolphin. I think that the two extremes, eat anything edible and vegan, are the easiest to defend. Any position in between is some sort of compromise. When I was vegetarian but not vegan, I would defend my position and admit that it was a compromise but closer to the vegan end than most.

  • I'm glad you posted this answer because I started to write about more and less strict practices within vegetarianism but decided not to shift the focus of my answer :)
    – Zanna
    Jan 13, 2019 at 12:30
  • 3
    @Zanna Thanks. I hope that our answers complement each other well. I could not have easily given the detail that you gave.
    – badjohn
    Jan 13, 2019 at 12:58

As a supliment to the other answers which only cover animal rennet:

Vegitarian Rennet is vegitarian, as it is not derived from animal sources (ie. made using animal parts as animal rennet is):

Vegetable rennet is a natural enzyme that coagulates milk and separates the curds and whey when you are making cheese. Commercial vegetable rennet is often extracted from a mold called mucor miehei. Vegetable rennet is used by vegetarian cheese makers to avoid adding rennet made from animal parts. The main ingredient for homemade vegetable rennet may be growing in your backyard or a forest nearby. You can make a variety of fresh and aged cheeses using homemade vegetable rennet.

By Jeffrey Brian Airman

Thus it is said by the commercial website I took the quote from, the way you can make your own is straightforward:

  • Boil some (washed) stinging-nettle leaves and stems in enough water to cover them and no more for about twenty minutes. Sieve out the solids, squeezing them for fluid and discard. (You can eat them like spinach, but without the stems.)

  • Use about 1/2 cups of the liquid for every 8 pints of whole milk (roughly 4.5 litres), stir and follow instructions as you would for animal rennet.

  • Any excess can be stored in the fridge for a week, or frozen.

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