What are these little crystals in my Cheese?

Question

In some Mature Cheddar, whilst slicing with a knife, I've noticed some tiny crystals.

What are these crystals are they a sign of good Cheddar or not?

Answer 1

To quote On Food and Cooking (Harold McGee), page 63, about crystals in Cheddar:

In aged Cheddar, there are often crystals of calcium lactate, formed when ripening bacteria convert the usual form of lactic acid into its less soluble mirror ("D") image.

In blue cheeses:

The white crystals often visible against the blue mold of a Roquefort, or detectable in the rind of a Camembert, are calcium phosphate, deposited because the Penicillium molds have made the cheese less acid, and calcium salts less soluble.

And, in other aged cheeses:

In Parmesan, Gruyere, and aged Gouda, the crystals may be calcium lactate or else tyrosine, an amino acid produced by protein breakdown that has limited solubility in these low-moisture cheeses.

So, basically there are a variety of salts present in the milk, and formed from milk by the action of bacteria and molds. As the cheese dries, and ripening micro-organisms act on the cheese, these salts fall out of the solution and crystallize. Personally, I love the slight crystalline texture present in aged cheeses, as it almost always comes with a robust and mature flavor.