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What is Rennet?

Mary McMahon
Updated May 16, 2024
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Rennet is an extract from the fourth stomach of young ruminants, such as cows, goats, and sheep. It contains a number of enzymes that are designed to help these animals digest their mother's milk, and when added to milk, it will cause the milk to coagulate, forming the curds and whey that are so essential in the cheesemaking process. Humans have been working with the extract for thousands of years, and it is typically readily available in stores that carry cheesemaking supplies; it can also be made at home, if you happen to have access to the necessary ingredients. For vegans and kosher Jews, non-animal alternatives to rennet are available.

There is a great deal of mythology surrounding the history of cheesemaking, because humans have been making it for a very long time, and the steps involved are actually fairly complicated. The stomachs of ruminants have historically been used to make bags and sacks, and food historians theorize that someone must have stored milk in one a bit too long, allowing it to curdle, and the curdled milk was then turned into a food product. Modern rennet is created through an extraction process that yields neat, dry tablets or a liquid that is very easy to work with.

Traditional rennet was made by washing the stomach of a young ruminant after it has been slaughtered, and then salting it. The salted stomach is kept in dried form, with cooks snipping off small pieces and soaking them in water when they have a need for the extract. Some cheesemakers continue to make and use it in this way, but the vast majority use commercially processed rennet, which is made by creating a slurry and then subjecting it to a compound that will cause the enzymes to precipitate out.

The main enzyme in the extract is rennin, although there are a few others, and the precise content depends on the animal the it comes from; sheep rennet, for example, is different from that from a cow. When added to milk, the enzyme causes the milk to coagulate, essentially starting the digestion process. Once curds have formed, cheesemakers can cut them, drain them, and pack them into molds to make cheese.

Several plants produce natural rennet compounds, as do some microbes, and these non-animal sources can be found for sale in stores that cater to vegans, and in shops that produce kosher dairy products. Vegans should be aware that cheesemakers are not required to disclose the source of their rennet, so unless a cheese is specifically labeled as vegan, it may contain extracts from an animal. Under Jewish dietary laws, milk and meat cannot be mixed together, so cheese that is certified as kosher or pareve will not contain the extract. It is also possible to find cheeses that have been coagulated with acids like lemon juice; paneer is one such cheese.

DelightedCooking is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a DelightedCooking researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments

By anon995641 — On May 16, 2016

Four types of Rennet: From the stomach lining of a calf, ewe or kid (baby goat); the plant rennet; genetically engineered rennet or fermentation-produced rennet; microbial rennet.

My being lactose (and gluten) intolerant from the get go as well as being unable to tolerate several other animal proteins made it impossible for me to ever eat any cheese without immediately experiencing severe abdominal pains afterward.

Through many years of paying attention to which particular foods I could not tolerate, I finally (just recently) delightfully discovered I can eat plain (with no additional seasonings added in) dry cheddar cheese curds made with microbial rennet without any pain whatsoever -- those "squeaky" short and bent pieces of cheese that all stick together and are usually sold in small bags at the dairy, in both white or orange cheddar (which is colored with annatto). I'm so happy. (Can't eat any grains either. But those I don't miss at all!)

By anon989963 — On Mar 29, 2015

First off, people need to not talk about stuff they don't know anything about. The term "baby" when referring to the veal calf is far from the truth. Veal calves are between 600-800 pounds, about 8-10 months old and are of specific breeds. They are far from "babies." Since the average bovine only lives for 18-20 months they're middle-age.

I find it interesting that we as the human race are OK with killing unborn babies and yet we're against harvesting animals for food. And yes, God did say that we can eat animals. Read Genesis 1. Genesis 1:28 God blessed them (humans) and said to them, "be fruitful and increase in number; fill the earth and subdue it. Rule over the fish in the sea and the birds in the sky and over every living creature that moves on the ground". God also had to kill a animal to clothe Adam and Eve after they had sinned.

I have to say that we need to treat the animals with respect. Animal rennet production is also utilizing an otherwise useless item that would just be rendered, so animal rennet is actually a recycled product!

By anon948901 — On May 02, 2014

"God" did not give us the animals to eat them. Animals are on this planet to harmonize and live among humans, not be tortured, kept in tiny cages, starved, beaten, and victimized every day because of greedy humans eating them all when they were here on the earth before us.

By anon945058 — On Apr 10, 2014

I bought cheese this past week, had this ooze coming out from a break in the cheese. I have contacted our Canada Food Inspection Agency about it. Is it rennet?

By anon942589 — On Mar 28, 2014

If rannet is obtained from an animal which is not slaughtered by the Muslim method, then all those cheeses are not halal and cannot be consumed by Muslims.

By anon937376 — On Mar 05, 2014

People who voluntarily consume this are disgusting. It's a true reflection of how gluttony and greed win over morality and ethics in people.

By anon925157 — On Jan 10, 2014

There is a website that lists many popular cheeses and whether they are made with rennet or not. I am severely allergic to rennet and rely on cheese that is made with other enzymes much more than any of you. Here are a few answers to questions I have read on this page:

Kraft is the worst when it comes to cheese. 100 percent of the time, their products contain rennet.

Land O' Lakes is not the only company that states on the label that the cheese is not made with rennet! Cabot is another one for example.

By anon342308 — On Jul 19, 2013

What can be used as a substitute for rennet? I can't buy it anywhere.

By anon315064 — On Jan 21, 2013

It's all food. God gave it to us to eat.

By anon313363 — On Jan 11, 2013

There is, for all practical purposes, no such thing as kosher rennet. Sure, you could make rennet from a kosher slaughtered cow and that rennet would be kosher, but you still couldn't use it to make kosher cheese! That would be a mixture of meat and dairy which is forbidden in kosher.

When looking at cheese labeling, it will say "kosher enzymes", not "kosher rennet". Kosher enzymes will be vegetarian always. If anyone actually sees the words "kosher rennet" on any product, I will be shocked.

By anon308941 — On Dec 13, 2012

Land O' Lakes brand cheese is the only one that makes the explicit claim that no animal rennet is used in the manufacturing. So, for strict vegetarians and for Hindus, that is the cheese of choice.

By anon295385 — On Oct 06, 2012

Can trypsin or chymotrypsin tablets be used directly instead of rennet?

By anon196292 — On Jul 14, 2011

My question to you is if rennet can have an impact on my digestive system? I have some reactions when I eat cheese. I love cheese but right after I eat it I get cramps in my back. I have to mention that some goat cheeses do not have that kind of effect on me, so that makes me wonder if I am allergic to rennet?

By anon180827 — On May 27, 2011

I would like to know if rennet comes from pork?

By anon167314 — On Apr 12, 2011

@Anon163620: The reason large manufactures do not use animal base rennet is because of the cost. Anon162035 is correct; the stomachs cost too much and the process is labor intensive. I should know because I make rennet in a factory! My company is probably the only supplier of animal based rennet in North America as of now! Most animal based rennet is made in Europe. The companies we supply are specialty cheese companies in Wisconsin and in Europe/Canada.

The proper name for describing a cow's stomach is called a "vell." Rennet is something disgusting when you make it, but not when it's ready for packaging.

Kosher Rennet is not vegetarian! Anon21859 is correct. The process in which the animal is slaughtered determines if it's Kosher or not. The same goes for the equipment used in the rennet process. Our equipment must be certified Kosher by a Rabbi before use.

By anon163620 — On Mar 28, 2011

I have a question: why would cheese companies *not* want to put this type of rennet in the ingredients? Does using non-animal rennet make the cheese seem "cheaper" tasting? I keep a mid-level range of kosher. If I can assume that most cheeses made in the US do not use animal rennet, then I can finally eat pizza again!

By anon162035 — On Mar 22, 2011

Note to 103271:Rennet is a) not disgusting; b) in the USA very rarely made from ruminant stomachs due to its cost and the popularity of cheese; c) not heartless-heartlessness would be wasting any part of a food animal that could be put to good use. We have not "become" more anything. Boiling shellfish, making cheese, raising geese/ducks for foie gras are all food practices that have been with us for thousands of years. So there!

By shepherds — On Mar 01, 2011

kosher rennet had no animal products in it except maybe dairy. if a kosher cheese is labeled parve, it has has no meat or dairy products in it. it may however, include eggs or if labeled fish. usually they use whey. Any animal bi-products will render it not kosher.

By anon140331 — On Jan 07, 2011

Okay, first of all, please excuse my ignorance, but are microbial enzymes, the same as rennet? All cheeses that I checked out in the grocery store had microbial enzymes listed. Plant or animal? How can I tell the difference? I am a vegetarian, and this is really important information to me. Thanks, Kate 61

By anon111230 — On Sep 15, 2010

You get animal rennet, rennet from GMO origin, coagulating enzymes from plant origin (like figs) and coagulant from non-GMO origin.

By anon104287 — On Aug 16, 2010

Rennet is hard to get in Zimbabwe also. Is there any substitute available such as lemon/lime juice?

By anon104193 — On Aug 15, 2010

Being veggie for 25 years, cheese was hard to give up. We have vegan cheese out here but look at the salt content. It far exceeds the amount in regular cheeses.

By anon103271 — On Aug 11, 2010

Rennet is from a young Ruminant. The way they obtain this disgusting substance is to take a baby calf just born from its mother and murder it before it can wean. Nice practice, and with the addition of goose pate and boiling lobsters alive, we've become heartless.

By anon102564 — On Aug 08, 2010

Correction! Kosher cheese can be made with kosher animal rennet. It is no longer common in the US to use animal rennet but still very common in Europe.

Look up Star K or Rabbi Avraham Gordimer

By anon95303 — On Jul 12, 2010

I would like to know if kraft cheddar cheese containing cow's rennet is edible for hindus.

By anon90204 — On Jun 15, 2010

does rennet have any pork extract?

By anon68606 — On Mar 03, 2010

I am a cheese maker from wisconsin and have been doing so for 15 years. We use rennet for your making of cheese. it is not cut from the stomach of small animals. it's made in a factory.

i am not jewish but all jugs that we get are certified kosher by Don Youel Levy, along with your coloring, which by the way is a vegetable extract.

By anon66778 — On Feb 21, 2010

I would like to correct the second comment, made by anon21859. Rennet made from kosher animals is not considered kosher for cheesemaking by practically all kosher-keeping, religious Jews. It is still considered a mixture of milk and meat, which is not permitted according to Jewish law. Cheeses which use this "kosher animal" rennet are not eaten by kosher-keeping Jews - it is just a marketing ploy to fool those who do not know any better into buying the company's product. Tablet-K certification is notorious for certifying these types of cheeses. Actual kosher cheese is made from vegetable rennet and will bear a reliable certification like Circle-K or O-U.

By anon53550 — On Nov 22, 2009

anon11989 - It depends on your definition of disgusting. Animal rennet comes from baby animal stomachs. You can make your own at home and it is much like making jerky.

Cut/slice the animal stomach and cure it, then dip it in what you are making - the enzymes work their way through the product and is then removed.

Rennet in spaghetti sauce - confusing to me. However, most rennet used in commercial cheese comes from vegetables because it's cheap. I think it would be safe to think that this is the case with your sauce. It's a thickening agent causing coagulation. Hope this helps.

By anon49503 — On Oct 21, 2009

Are there any substitutes for rennet, e.g. can I use lemon or lime juice or citric acid to make mozarella cheese? we can't find rennet suppliers in Malaysia.

By BertramTen — On Apr 16, 2009

Hi, I am lactose intolerant and trying to find cooking substitutes.

Does rennet contain lactose?

By anon27909 — On Mar 07, 2009

You do not need to avoid rennet. Cheese is made using a small amount of rennet, many puddings are made utilizing it. My people were Swedish, and we still make a desert at Christmas called Ostakaka, which requires rennet to set the milk.

By anon21859 — On Nov 23, 2008

I used to think that Kosher rennet was vegetarian, but have since found out that if the rennet is obtained from an animal that is slaughtered in a kosher manner, it can usually be used in kosher cheese because it is considered to be changed so much from the original animal that it is OK to mix with dairy.

By anon11989 — On Apr 28, 2008

I still do not understand if rennet is something disgusting. I bought a jar of spaghetti saue w/ rennet in it and want to know if it is something i normally would avoid.

Mary McMahon

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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