One of the distinctive features of Gruyere and aged hard cheeses (like Parmigiano-Reggiano, Italian grana cheeses, and fine aged cheddars) is the presence of tiny, hard crystals. I've been curious about them for a while, so I dove into the library to find out where they come from and what they are made of.
After the curd has been salted and formed into the appropriate shape (and perhaps salted on the outside or coated with something, like ash or cloth or wax), the 'pre-cheese matter' starts to undergo a transformation. Bacteria in the mixture consume milk sugars to produce lactic acid, enzymes snip apart proteins, fats are chopped up, and other chemical reactions occur to create the distinctive flavor of that particular cheese. And, it seems, substances fall out of the solution to form crystals.
On Food and Cooking says that the crystals in aged cheddar are calcium lactate, which is created by interactions between beneficial bacteria in the cheese and lactic acid. When enough of the chemical is in one place, a crystal can form. In parmesan-type cheeses, Gruyere, and other aged cheeses, he writes, the crystals can be either calcium lactate or tyrosine, an amino acid that is insoluble in low-moisture cheeses. Tyrosine crystals result from protein breakdown during cheese ripening.
The Manufacture of Extra-Hard Cheeses entry in the Encyclopedia of Food Sciences and Nutrition has a few paragraphs about cheese crystals. In grana-type cheeses, a first type of crystal appears in the first hours of ripening. These spherical crystals are calcium phosphate, and like calcium lactate, are the product of bacteria interacting with the cheese. They are about 10 micrometers in diameter (a human hair ranges from about 20 to 180 micrometers in diameter). A second type of crystal is needle-shaped and occurs at the end of the ripening period, with dimension of about 5 micrometers long by 1/2 micrometer wide. These are calcium lactate. (The dimensions of the crystals provided in this reference seem a little small to me, based on my experience with cheese crystals, so perhaps I'm detecting clusters of crystals.)
The official site of the Consorzio del Formaggio Parmigiano-Reggiano (the trade organization that governs production and marketing of the cheese) talks about the crystals in their FAQ:
What are the small grains you feel under your teeth when you eat a piece of Parmigiano-Reggiano?
Unlike what many people think, they are not grains of salt nor grains of calcium. They are crystals of an amino acid, called tyrosine, which, owing to its molecular conformation, crystallises if it is free and in high concentrations. Together with other amino acids, it is released during the process of protein breakdown triggered by enzymes. Therefore the presence of tyrosine is definitely a practical indication (since it can be experienced by every consumer) of a good degree of maturation of Parmigiano-Reggiano.
To sum up, the transformations that occur during cheese ripening — protein fracture, fat splitting, bacteria consuming sugars — can create localized concentrations of certain chemicals that can coalesce to form insoluble crystals. I'm certainly not bothered by them, and usually think of them as a sign of a cheese that has been produced in the traditional manner.
Photo of a round of Parmigiano-Reggiano cheese from surfzone's flickr photostream, subject to a Creative Commons License. Photo of aging Gruyere cheese from Sopra Mais' flickr photostream, subject to a Creative Commons License.
Random link from the archive: Dried Red Chiles
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