Most vegetarians (and the people who cook for them) assume that real Parmesan-Reggiano cheese is vegetarian, since it’s made from animal byproduct and not the animal itself. However, this classic Italian cheese is made according to very strict specifications, which reveal that it’s not as vegetarian as you might think.

True Parmigiano-Reggiano cheese is made with rennet, which comes from the lining of a calf's fourth stomach. It contains chymosin and pepsin, two enzymes that play an essential part of curd formation in the cheese-making process, which means that true Parmesan cheese is technically non-vegetarian.

Luckily there are alternatives, like using the rennet from artichoke and nettle enzymes during the cheese-making process in place of the cow's stomach. The website Vegetatio provides a list of vegetarian cheeses and brands, including "Parmesan," that should be acceptable to most vegetarians — even if it isn’t true Parmigiano-Reggiano.