A chemistry lesson, courtesy of The Kitchn:
Ever wonder about the whitish spots of crunch in your cheese? People have a wide variety of theories on those little crystalline bits. No, it's not salt, it's not something deliberately added during cheesemaking, it's not that the cheese is old and it's starting to dry out, and it's not a cheese mite. Today we're setting the record straight in a big reveal of the little known component in some of your favorite cheeses.
Those bits are called tyrosine, and they're actually amino acid clusters that form with age. Tyrosine clusters are signs of a well-aged cheese, which is why you'll find them in some of the world's most loved cheeses like Parmigiano Reggiano, aged goudas, and mountain cheeses like gruyere or Pleasant Ridge Reserve. Tyrosine is a non-essential amino acid found mainly in casein, the dominant protein found in milk. The word itself is from the Greek tyros, meaning cheese.
What's most fascinating (from a dorky cheese fanatic perspective) is the reason that these protein clusters form. When cheese is made, fats and proteins are trapped within chains of proteins that have bonded together during acidification. Groupings of these fats and proteins make up the solids, or curds, that form cheese. When cheese spends a long time aging, these protein chains begin to unravel, leaving small, crunchy deposits behind. Tyrosine lends a distinctive textural charm to cheese, and is a welcome interruption within the body of an otherwise smooth paste. And sometimes it even compliments the beverage you may be drinking with your cheese, as in the case of pairing a full-bodied stout with a super-aged cheddar; the crunchiness of the cheese somehow matches the fullness of the beer by contributing its own textural intensity.
Tyrosine is not to be confused with the crunchiness you can find in some washed-rind cheeses. Since this category of cheese is usually washed in some kind of salt water brine, residual salt crystals are often left behind on the crust of these cheeses. When you take a bite of rind and inner paste together, the crunchiness from the outside can be mistaken for existing on the inside. Now go and impress your cheese-loving friends with your new vocabulary word!