What Is Non-Animal Rennet, and Is It in Your Cheese?

Short answer: non-animal rennet is the enzyme that sets most modern cheese, made by fermentation instead of taken from a calf's stomach. Lab-grown microbes produce chymosin, the same curdling enzyme found in traditional animal rennet, so the milk sets the same way without an animal. It's in roughly 80 to 90 percent of commercial cheese, and on a New Zealand label it shows up as "non-animal rennet" or just "enzymes." Here's what that actually means, and which cheeses on the shelf here use what.

Cheese is supposed to be one of the simple ones.

Milk, cultures, salt, time. Four things and patience. It's the food people reach for when they want something that feels older and steadier than the rest of the trolley.

Then you turn the block over and read "non-animal rennet," and the simple food has a line in it that nobody explains.

So here is the explanation. What rennet is, what the non-animal version actually is, how to read it on a label here, and the part most coverage skips: which New Zealand cheeses use which, and how many companies won't tell you.

What rennet does

Milk doesn't become cheese on its own. Left alone it sours, but it won't set into a firm curd you can press, age and slice.

The thing that makes it set is an enzyme called chymosin. Its one job is to cut a single milk protein, casein, at one precise spot. Make that cut and the milk separates: solid curds on one side, liquid whey on the other. Everything that follows, cheddar, gouda, brie, parmesan, starts from that one snip.

For thousands of years that enzyme came from one place: the stomach lining of young calves. Calves produce chymosin to curdle their mother's milk. Cheesemakers took the fourth stomach of a slaughtered calf, dried and salted it, and used it to set milk. That is animal rennet. It is the traditional method, and it is exactly as it sounds.

Where the lab version came from

Calf rennet has a problem built into it. The supply depends on how many calves are being slaughtered, which depends on the dairy and meat cycle, which has nothing to do with how much cheese the world wants. As cheese demand grew, the enzyme couldn't keep up.

In the 1960s, cheesemakers started using rennet from certain moulds and fungi instead. This is microbial rennet, and because no animal is involved, it made cheese that vegetarians could eat. It worked, though it could leave a faintly bitter edge in long-aged cheese.

Then in the late 1980s the real shift arrived. Biotech companies took the calf gene that codes for chymosin and inserted it into microorganisms, microbes that could then be grown in fermentation tanks and made to produce the enzyme on demand. The microbe does the calf's job. The enzyme it makes is chymosin, the same molecule, just grown in a tank instead of a stomach.

This is fermentation-produced chymosin, FPC, and it is what "non-animal rennet" almost always means on a modern label. It removed every limit calf rennet had. No slaughter cycle, no seasons, no ceiling. Cheese stopped being a biologically constrained product and became an industrial one that scales as far as the milk supply allows.

One detail worth holding onto, because it matters for how organic certification treats it. The microbe that makes FPC is genetically modified. The enzyme it produces is then harvested and purified, and the final ingredient contains no GM material. The production organism is GM; the thing that ends up in your cheese is not. The standards lean hard on that distinction, which is a story in its own right, and one I got into with a specific block of supermarket cheese in Mainland Organic Cheese: Is Non-Animal Rennet Legit?

How it reads on a New Zealand label

Here is where the transparency runs out.

On a NZ ingredient list, rennet is treated as a processing aid, not a primary ingredient. That classification does a lot of work, because processing aids carry far lighter disclosure rules. The result is that a profoundly different production method can hide behind two of the vaguest words on the packet.

What you'll see is one of these:

• "Non-animal rennet" — almost always fermentation-produced chymosin, made by a GM microbe.
• "Enzymes" — could be FPC, could be microbial. The word tells you nothing.
• "Animal rennet" — the traditional calf-derived kind. When a company uses this, they usually say so, because for some cheeses it's a selling point.
• "Vegetable rennet" or "microbial rennet" — the fungal kind, no animal, no GM microbe.

The source, animal, microbial or fermentation, is not required on the label. So a cheese can be the product of precision biotechnology and read like it came off a farm in 1950, and both descriptions are technically honest.

Which NZ cheeses use what

This is the part nobody quite pins down, and now you can see why. The label won't tell you, and the law doesn't make the maker tell you either. So the only way to know is to ask the companies directly, and when people have, the answers split into three groups.

The ones that tell you. Mainland publishes it on their own FAQ: most of their rennet is microbial and vegetarian, but they still use animal rennet in a few products. Their conventional Tasty cheddar is set with calf rennet, and they say so on the label, because the traditional enzyme ages and develops flavour in a way the lab version doesn't. Their certified organic block, by contrast, uses non-animal rennet and carries the Suitable for Vegetarians mark. Same company, same factory heritage, opposite enzymes, sorted by who buys each product. I pulled that thread all the way through in the Mainland Organic piece, and it's the cleanest example of the whole tension on one shelf.

Fonterra's ingredients arm, which supplies a great deal of the cheese sold here, states the same pattern in plainer terms: most of its cheese is made with vegetarian rennet, with animal rennet used "to suit requirements."

The ones that won't. When New Zealand researchers and food writers have rung around asking which rennet each brand uses, a striking number simply declined to answer. A 2025 enquiry documented by the Hatchard Report found Whitestone in Oamaru, Mahoe in Northland and Hohepa in Hawke's Bay all said they use microbial, plant-based rennet rather than fermentation chymosin; Barrys Bay in Canterbury said it uses fermentation chymosin exclusively; and Mainland, along with Goodman Fielder, which makes Puhoi and Ornelle, would not give a clear answer. A separate consumer enquiry reported the same wall of silence from several brands, with only a couple willing to confirm what they use.

Sit with that for a second. A company knows exactly which enzyme it puts in its cheese. It is not a trade secret; it is an ingredient. When a customer asks and the answer is "no comment," that is a choice, and it is the most telling data point on this whole page. The cheeses that use the traditional calf enzyme tend to say so proudly. The cheeses that use the lab enzyme have every incentive to stay vague, because "non-animal rennet" sounds clean and "fermentation-produced chymosin from a genetically modified microbe" does not. Non-disclosure isn't neutral. It usually points one direction.

The supply shift underneath all of it. Renco, the rennet long used across the New Zealand industry, stopped production in 2025. Quietly, a piece of the country's cheesemaking supply chain closed, the kind of thing that never makes the news but reshapes what ends up in the curd.

I'm not going to print a definitive brand-by-brand table here, because most of it would rest on phone calls I can't verify and answers companies could change tomorrow. What I can tell you is the rule that actually works at the shelf, below.

The vegetarian paradox

Here's the part that turns the whole thing on its head.

Most vegetarians eat cheese. Lacto-vegetarians, the most common kind, eat dairy by definition. Cheese is a staple. And yet traditional cheese, the old, simple, four-ingredient kind, is set with an enzyme taken from the stomach of a slaughtered calf. By the strict logic of vegetarianism, classic cheese was never vegetarian at all. A calf died to make it.

So how is there a "Suitable for Vegetarians" mark on cheese? Because of the lab.

The exact ingredient the natural-food world is most suspicious of, the GM-microbe fermentation enzyme, is the precise reason a block of cheddar can be vegetarian-friendly. Animal rennet is the "natural," traditional one, and it's the one with a dead calf behind it. The industrial, high-tech one is the one with no animal in it at all.

Read the shelf with that in mind and it gets genuinely strange. The shopper avoiding biotech reaches for the most traditional cheese and picks up calf rennet. The vegetarian avoiding the calf reaches for the cheese set by a genetically modified microbe. The "clean" choice and the "natural" choice are pulling in opposite directions, and the label that's supposed to help, "non-animal rennet," is the one doing the least to explain itself.

There's a flavour wrinkle too, and it's why Mainland keeps calf rennet in the Tasty. Animal rennet isn't a single purified enzyme. It carries supporting enzymes that keep working through maturation, breaking down proteins and fats, building the depth and sharpness you want in a long-aged cheddar. Fermentation chymosin is purified and consistent, which is ideal for scale but milder in the ageing. For everyday cheese the difference is small. For a serious aged block, the old calf method still wins on taste. So the traditional, less fussy product is sometimes the better-tasting one, and the premium, "cleaner"-sounding one is the biotech version. The paradox runs all the way down.

So what should you actually do at the shelf

There's one rule that survives all the vagueness:

If the source matters to you, the cheese has to tell you, and if it won't, assume the lab version.

• Want to avoid the GM-microbe enzyme? Look for "animal rennet," "vegetable rennet," or "microbial rennet" stated explicitly. If it just says "non-animal rennet" or "enzymes," it's almost certainly fermentation-produced chymosin.
• Vegetarian and want no slaughtered calf in it? Look for "non-animal rennet," "vegetarian rennet," or the Suitable for Vegetarians mark. The lab enzyme is your friend here, not your enemy.
• Want neither calf nor GM microbe? That's the narrow path: cheeses that state plant or fungal microbial rennet, like some of the smaller NZ makers who'll tell you. You'll usually have to go to the maker, not the supermarket block.
• Brand won't say? Treat the silence as an answer. A company proud of calf rennet says calf rennet. Vagueness is the FPC tell.

None of this makes any of these cheeses unsafe. Fermentation chymosin has been in the food supply for over three decades with no demonstrated harm, and it's classified as safe by every regulator that's looked. This was never really a safety question. It's a transparency one, which is the whole point of this site: not what's dangerous, but what you're not being told.

Before you go

You just read the back of the label so you didn't have to puzzle over it in the dairy aisle. That's the job here. One piece most days, pulling apart what's actually in New Zealand's food and who makes it. Free to read. No ads. Nothing behind a wall.

If that's useful, the easiest thing you can do is let the next one find you.

→ Get it in your inbox

Or back the work directly. A one-off $10 covers the digging. No account, no subscription.

→ Chip in here

Related reading from OFT:

• Mainland Organic Cheese: Is Non-Animal Rennet Legit? — the whole tension on one supermarket block, and how a GM-made enzyme ends up in a certified organic cheese
• What does the organic label actually mean? — the four NZ certification bodies and what each one audits
• The Real Food Map — makers and shops where the supply chain is short enough to see the whole thing