I notice in Parmesan cheese sometimes that there are crunchy little grains.  What are they and what causes them?  Do they mean that the cheese is no longer good?

--Anja

The grains you are noticing are crystals of either calcium lactate or the amino acid tyrosine.

Tyrosine is formed by the breakdown of proteins in the milk.  It precipitates out as crystals as the cheese loses moisture, rather in the same way that crystals form in a sugar water solution as it cools down.

Calcium lactate crystals are formed by the bacterial conversion of lactic acid into a mirror image form during ripening.  In either form, lactic acid will chemically bond with the calcium in the milk to form calcium lactate.  Because the mirror image form of lactic acid is less soluble, it precipitates out and forms crystals.

I recently encountered the same crystals in a delicious cheese called Beemster that I got at the Bulk Cheese Warehouse in Saskatoon.  Beemster is a Dutch Gouda-style cheese that has been aged for 18 to 26 months or longer.  It is sometimes referred to as Extra Aged Gouda.  The taste is somewhat like Parmesan, but with a caramel, nutty flavor slightly reminiscent of Gjetost.  The texture, however, is more buttery probably due to a fat content that may be nearly twice as much as that of Parmesan.

Other softer cheeses may also form crystals due to changes in the acidity of the cheese.

These crystals are a normal phenomenon, and do not mean that the cheese has gone bad.