Blame a little something called rennet.
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Cheese: the saving grace of many a vegetarian who still wants to treat themselves, or the one thing arguably standing in the way of them going full vegan. Alongside eggs and milk, cheese is a useful way for non-meat eaters to easily ensure they're still getting a certain amount of protein in their diets, all without as much of the guilt that may accompany the eating of actual animals. 

Well, as it turns out, not every cheese is created equal, in the sense that not every cheese is technically vegetarian. If you're a vegetarian who's a big fan of pasta, caesar salads, or general Italian cooking, I hope you're sitting down as you read this: Parmesan cheese isn't vegetarian. 

So why isn't Parmesan cheese vegetarian? 

Great question. In this case, it has to do with the use of something called rennet, which is pretty crucial to the Parmesano-Reggiano production process. Rennet is usually taken from the fourth stomach of a relatively young grazing animal like calves, goats, or lambs. That stomach is prized for its concentration of an enzyme called chymosin, which gradually loses its potency over time as grass replaces milk in that animal's diet. 

Traditionally, getting that rennet has meant slicing the stomachs of young calves into little pieces dropped into salt water or whey, with something acidic like wine or vinegar used to help draw out the enzymes. Once that solution's filtered out, it can coagulate a significantly larger quantity of milk. More modern methods use a bit of more precise chemistry to yield more potent rennet, but a calf's stomach is still involved. 

pieces of parmesan cheese on a wooden cutting board
Credit: Mauro69/Getty Images

What is rennet's role in the Parmesan process? 

If it makes you feel any better, those stomachs play a crucial role in making Parmesan cheese what it is, thanks to the ability of chymosin to separate solids from liquids in the cheesemaking process.

When producing Parmesan, rennet is introduced after unpasteurized cow's milk is heated, in order to start the separation process. From there, not much else is really added as the cheese does its thing over time. In fact, a cheese can only meet the European Union's legal definition of Parmesan if it's produced in the "Reggiano" region of Italy using nothing more than cow's milk, salt, and calf rennet, underscoring how central that bit of stomach is to the process.

Do other cheese also use rennet? 

It brings me no pleasure to report that Parmesan is far from the only cheese in which rennet plays a role. You'll find rennet in other Italian cheeses like Pecorino Romano, Grana Padano, and Gorgonzola (which is now stinky to vegetarians for non-olfactory reasons). 

Certain French and Swiss cheeses also, regrettably, say oui to rennet. They include Camembert, Vacherin, Emmenthaler, and Gruyère. Even Spanish Manchego can't resist rennet's role in the curdification process. 

Are there vegetarian-friendly alternatives to those cheeses?

While northern Italians may quibble with their authenticity, the good news for vegetarians is that there are viable (though perhaps less genuine and/or tasty) alternatives to Parmesan and other European cheeses that bypass the rennet.

Instead, those truly vegetarian cheeses get the coagulating, curding magic they need from microbial enzymes that mimic the effects of chymosin. Various plants can also provide a "vegetable rennet" of sorts. Boiling cardoon thistle, artichokes, or nettles in water and straining the end result with a cheesecloth leaves behind a thickening enzyme functionally similar to chymosin. Certain Iberian cheeses like Azeitão are traditionally made using plant rennet, meaning vegetarians may have better luck shopping for Portuguese or Spanish options. 

Before you get too excited, though, there's a reason that non-animal alternatives to rennet aren't as popular as the genuine article. Supposedly, they can be a bit fussier to make cheese with than an actual calf stomach, and the flavor might come off a little bit different as well. 

Failing that, you can always opt for a vegan alternative. With the revolution in plant-based alternatives going on these days, you may just be pleasantly surprised with how decent a vegan imitation of your favorite rennet-based cheeses tastes.

Up until a few minutes ago, you may have lived your life totally unaware that the cheese you enjoy on top of spaghetti or caesar salads has more in common with veal than you'd like to believe. But while ignorance may be bliss, knowledge is power. Learning about rennet certainly doesn't make vegetarianism any easier, but now you can at least seek out alternatives to the "meat" you've unwittingly consumed. 

Or you can just keep on eating whatever cheese you want without giving a second thought to any of this, because cheese is tasty. The choice is yours. 

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