Should I choose animal rennet or vegetable rennet in my natural cheese?

Miller’s Bio Farm is all about giving you TMI about how your food was produced. Because, in today’s food world, you can’t just rely on labels alone. 

When you shop our A2/A2 CHEESE, you can click on each cheese and see the full product description. You can find the exact kind of rennet in the ingredient list. And, you can see any trace additives used in the cultures or rennet listed in the “Honest Disclosure” section. 

But what does that all mean, and which type should you choose? How would you know which type is used? That's what we're delving into in this blog post -- it's all about rennet!!!

What is Cheese? What is Rennet?

Legend has it that cheese was discovered by mistake, when someone used a flask made of lamb stomach to bring some nourishing milk on their travels. After walking for days in the hot sun, he found that the milk in his flask had curdled… and it was delicious! The raw milk naturally fermented, and the enzymes in the lamb stomach coagulated the curds.

Cheesemaking has come a long way since then, with specific processes and cultures needed to make different kinds of cheese. And then of course there’s regulations around food and food safety and modern expectations for consistency and affordability.

Here's an overview of how cheese is made today --- You add culture to milk and let it ferment. Then, you add rennet, which separates the milk into curds and whey. Then you press the curds and age them. Voila cheese!

Sure, you can also use vinegar or citric acid to curdle the milk for fresh cheeses like paneer, ricotta, or even mozzarella. But, for aged cheeses, you need to use rennet. It's essential.

Rennet is a complex set of enzymes that are naturally produced in the stomachs of ruminant mammals. Chymosin, its key component, is a protease enzyme. In addition to chymosin, rennet contains other enzymes, such as pepsin and a lipase.

The enzymes in rennet target casein, the main protein in milk. They cause the casein molecules to divide and re-coagulate into even larger clumps (AKA cheese curds).

Above photo of how the cultured and fermented milk sets after rennet is added.

Above photo of how the curds and whey look after the curds are cut and heated a bit.

Above photo of how the curds look after the whey is drained, before pressing the cheese. 

Types of Rennet

Veal/calf rennet: Made by grinding calf gullet/stomach and mixing it with salt. The powder is put in a solution that extracts the chymosin. It’s typically made as a liquid rennet.

Veal/calf rennet is the most natural form of rennet, since it’s the oldest form of rennet. Remember, carrying milk in a lamb stomach was likely how cheese was discovered!

Using veal/calf rennet in today’s world is not all pure and natural. Most rennets available are made from calves that are a byproduct of the conventional dairy industry. They are not likely born from happy, pasture raised cows that are 100% grass-fed. And, almost all of them contain trace additives of one kind or another. These may include sodium acetate, propylene glycol, or potassium sorbate.

Fermentation-produced chymosin (FPC): It’s a genetically modified organism! They splice genes in a mold to produce chymosin. 

I spoke with a lab tech that makes the vegetarian rennet used in our goat cheeses. They weren’t sure how they can make the claim that it’s GMO-free, but somehow the rennet and cheese companies make that happen (with a lot of * and fine print below).

Fermentation-produced chymosin is the most popular rennet for certified vegetarian” cheeses. Over 90% of all cheeses made today use this kind of rennet. It makes a good product. As it stands now, it cannot be used in "certified organic" cheeses.

The concern here is of course that it’s a bioengineered ingredient. What are the long term health consequences of consuming it? Does the GMO chymosin enzyme alter the casein proteins differently than veal rennet? Well, there’s simply not enough research done to be 100% sure.

Another concern is trace additives like sodium chloride or sodium benzoate.

Microbial rennet: Made when Rhizomucor miehei mold grows on a nutrient base that’s primarily soy. Yes, that’s right, soy. And, that means that the nutrient base is most likely GMO! 

Mold rennet is also used in “certified organic” and “certified vegetarian” cheeses. However, it’s not the best. It tends to produce undesirable bitter flavors. It also does not age very well. 

Recent research is showing that microbial rennet can have a negative impact on the gut long term. It’s definitely something to be cautious about until a lot more research is done.

Rennet Alternatives: 

You can use squares of dried salted calf stomach, which has been done for thousands of years. You can use thistle, which is traditionally used for specific cheese in Spain and Portugal and is really expensive. You can also make soft cheeses from wild rennet from plants like sorrel, cardoon, artichoke, and fig. 

However, these rennets are typically used for making cheese at home. They would not produce a cheese that’s consistent, tastes good, and holds up well. Most farmers and cheesemakers would not want to dabble with them, as they’d end up with a lot of waste and unhappy customers. 

Is GMO Vegetarian Rennet Safe?

The safety of genetically modified rennet is a topic of debate, both in the scientific world and the regulatory world. Some studies suggest that it’s completely safe, and others raise concerns about potential allergic reactions or other concerning health consequences (read more about corn and soy and allergies in this post).

Why the debate? Well, there’s limited scientific data to definitively state the long-term safety of cheeses made with GMO rennet. In my opinion, it’s likely best to wait for full safety studies before introducing a product. Sadly, that’s not how our food world works. So, now that you know, it’s your choice whether you want to stay away from "vegetarian rennet" or not!

It’s important to note that the safety and regulatory status of GMO rennet varies from country to country. While in some places, GMO rennet has been deemed safe and approved for food production, in others, it might be subject to restrictions or even prohibited altogether. Depending on local laws, cheese made with GMO rennet can be labeled as GMO-free (and that’s how it is in the US).

Labeling Requirements

With cheese, it’s required to list “rennet” or “enzymes” as an ingredient. But, the source (animal, plant, or microbial) is NOT required. For cheese companies that make cheese with vegetable rennet, the have the option of listing “vegetable rennet”. But again, the exact kind is not required on the label.

Additionally, listing the ingredients in the ingredients is also not required. For example, a cheese may say "rennet" in the ingredients list, but the sodium acetate, propylene glycol, or potassium sorbate or other additives does NOT need to be listed on the label. The same is true for basically any trace additive in food.

So, if you want to know the type of rennet or trace additives in your cheese, you need to read the product description. If it's not there, you'll need to ask. 

What’s in Our Cheese?

At Miller’s Bio Farm, we of course go above and beyond. We do everything we can to avoid the greenwashing or confusion caused by food labels. Instead, we just tell you everything we can about how the food is produced. We include an honest disclosure for each of OUR A2 CHEESES, which tells you the type of rennet and any additives in them (and not just what's listed on the Safety Data Sheet, we actually talk to the rennet and culture companies about it).

For all of our cow and goat cheeses (except mozzarella), beef rennet is used. The calf gullets used in our rennet are sourced from milk-fed veal calves mainly from New Zealand and Australia. 

Sadly, it seems impossible to find a beef/veal rennet without trace additives. We were super excited to find Walcoren brand rennet, which did not have any additives on the safety data sheet. But, when I called the company and talked to a scientist, he confirmed that the standard additives are actually in it. Since they're a Canadian company, they don't need to include them in the safety data sheet. Ugh.

As with all beef or veal rennets, our rennet contains trace amounts of sodium acetate, propylene glycol, and potassium sorbate. 

For our mozzarella cheese, a microbial vegetarian rennet is used. It's organic and simply makes a better mozzarella. It has trace amounts of sodium chloride and sodium benzoate E211.

For our cottage cheese, no rennet is used at all. It's cultured, and the curds are separated with a little heat only.

To put all of this into perspective, you only need a little bit of rennet to make a whole lot of cheese. For example, our cheesemaker uses 60ml of rennet per 1,000 pounds of milk. That’s 1.93ml per 1 gallon of milk. Then, the curds are drained and pressed and fermented. In the end, In 1 lb of finished cheese, there's about 0.00066 grams of rennet. 

Any additives would be minuscule, a trace of a trace amount. But, if a trace of a trace amount of something bad is in everything you eat, it's no longer a trace amount! 

Regardless, you deserve to know everything about your food. So, now the cheese and rennet choice is yours!

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*Originally posted on 7/28/23. Updated on 1/23/25.