What Are Those White Crystals on My Cheese?

Parmesan is a potent pantry power player. Is your Caesar salad falling flat? Probably needs more Parmesan. Want some extra umami in your stock? Throw in a Parmesan rind, like test kitchen editor Kendra Vaculin does in her Gnocchi-Leek Soup With Greens. If you’re a seasoned (cooking pun!) Parmesan fan, you know how a few salty curls can transform a dish. But you’ve likely also encountered a mysterious crunch every few bites.

No, you’re not imagining things. There’s a reason you’re feeling a tingling crackle in the midst of your bite of cheese, and seeing itty-bitty white stuff when you cut a slice. Parmesan is full of crystals, and they’re just as special as they sound.

What are those little crystals in cheese?

Two kinds of crystals appear in cheeses. The first, as Josh Windsor, senior caves manager at Murray’s Cheese, explains, are actually amino acids, the building blocks of protein. There are hundreds of amino acids in nature, but the aminos that form those tiny crystals in cheeses are mostly tyrosine and leucine—these are the crunchy bits you’ll notice mid-bite.

The second type of crystal is made of a substance called calcium lactate—this forms those white powdery spots you see on the outside of your cheese. During the aging process, bacteria break down the lactose in the cheese into lactic acid. That lactic acid combines with the calcium present in the aging cheese to form crystals. These tend to appear on the surface of cheese, where moisture can collect.

In both cases, the resulting crystals are pretty tiny—the one’s you’ll notice as crunchy range in size from about as tiny as a grain of sand to as large as a mustard seed.

Do crystals indicate anything about the quality of cheese?

A lot of people confuse the white powdery look of calcium lactate on the surface of cheese with mold—an easy mistake to make. Calcium lactate will lay flat on your piece of cheese, whereas mold will be raised, growing on top of it. If it’s green or blue, you can be sure it’s mold—the bad kind—since calcium lactate is only ever white.

You might be familiar with those white spots on your Parmesan, but Windsor says crystalized amino acids are most commonly found in Alpine-style cheeses, such as Gruyère, as well as Goudas, blue cheeses, cheddars, and even Camemberts and Bries.

Since these crystals form during the aging process, more crystals usually indicates a more mature ingredient. And older cheeses are often more expensive. But it’s personal: Do you prefer a crystalline crunch every few bites? Or do you like your cheeses smooth and creamy? For Windsor, it’s all about the variety. “I love cheese crystals. They offer a textural contrast that is hard to find in other foods,” he says. “What’s not to like?”

Pass the parm

Sam Stone is a staff writer at Bon Appétit, covering restaurants, culture, and cooking. He has been vociferously eating Parmesan (including its crystals) for as long as he can remember.