What is Rennet?

What is rennet?

When reminded that nearly all cheese is made with only four ingredients – milk, salt, bacteria, and rennet – most folks will say, "That's amazing!" and then, after a short pause, "Um, what is rennet?"

Rennet is truly the unsung hero in the story of cheese. Milk usually gets all the credit, of course, but it's rennet that starts the transformation of a vat of milk into a block of blue cheese, a chunk of colby, or a wedge of white cheddar. The enzymes in rennet coagulate the milk and help separate the solid curds from the liquid whey, giving cheesemakers the raw material to create an amazingly varied collection of cheeses.

Here in Wisconsin, if you ask "What is rennet?" in any supermarket or cheese counter, you're likely to get a pretty astute explanation of the cheesemaking process. Of course, that's what you'd expect in a state where everybody dreams in cheese – and where we make more flavors, varieties, and styles of cheese than anywhere else in the world.

Take a cruise around our website to meet some of the amazing rennet cheese produced in Wisconsin. Search our recipe index to find cheesy ideas for a holiday feast, a game day cheese board, or a Tuesday night mac and cheese dinner. Or scroll down for more in-depth answers to all your questions about rennet's role in making cheese.

What is rennet? A quick cheesemaking primer

One of the essential ingredients in making nearly every kind of cheese, rennet is a set of enzymes that cheesemakers use to coagulate milk and separate solid curd from liquid whey.

Traditionally, the enzymes in rennet have been taken from the stomach linings of young ruminant animals like calves, lambs, and kids (young goats). This type of animal rennet has been used in the cheesemaking process for thousands of years. The power of rennet to coagulate milk was likely discovered when one of our early ancestors attempted to transport milk in pouches made from the stomach of a calf or lamb, only to discover that the milk became solid during the journey.

In addition to animal rennet, cheesemakers have used a variety of other types of rennet to introduce the enzymes in cheese that are critical to the cheesemaking process. Plant or vegetable rennet relies on the coagulating properties of thistle, nettles, dried caper leaves, artichokes, and other plants. Microbial rennet uses certain kinds of mold, yeast, or fungi to coagulate milk. And fermentation-based rennet uses genetic engineering to reproduce the same enzymes found in animals within bacteria, fungi, or yeast. Vegetable rennet, microbial rennet, and certain forms of fermentation-based rennet are considered vegetarian.

Rennet is sold in several forms. Liquid rennet is often used when making smaller batches of cheese, as it's easy to measure. Rennet in powder or tablet form may be used in larger operations because it has a longer shelf life.

Raving about rennet in Wisconsin

In Wisconsin, we love rennet in all its forms, because we know that a little rennet can lead to a lot of romano, parmesan, muenster, or marbled blue-jack. Our cheesemakers have been perfecting their rennet-based recipes for 180 years (since before we were even a state) and they've taken home a boatload of awards for their cheeses – more than any other state or nation in the world.

So, next time you want to sample some of the most amazing rennet cheese this planet has to offer, just make sure that chunk of cheese in your hand has a Proudly Wisconsin Cheese badge on the label. Trust us – your tastebuds will thank you.