parmigiano reggiano

Parmigiano reggiano (Bos taurus, aged cheese) appears once, in the carbonara, at the same weight as the pecorino: 25 g of each, finely grated. It is beaten with three eggs, two whole and a yolk, and a heavy grind of black pepper before the mix meets the hot pasta and the lamb's fat. The library lists butyric acid for its aged-cheese tang and glutamic acid for its umami.

The Journal's note on salt and bitterness names parmesan among the foods where sodium arrives with free glutamate, which is what a cook means by savoury, with the salt clearing the bitterness out of the way. The note on preservation says where the glutamate comes from: fermentation breaks proteins into peptides and free amino acids, and in hard Italian cheese the build-up is orderly enough to work as a clock. Pyroglutamic acid, the cyclised form of glutamic acid, reaches about half a gram per hundred grams in Grana Padano and Parmigiano Reggiano, and its concentration tracks the age of the wheel with an R squared of 0.94.

The carbonara note adds the hazard. Pecorino and parmigiano are hard, aged and low in moisture, and their casein is held in a network cross-linked by calcium. Heated in a watery sauce, the proteins pull tighter on each other instead of dispersing. The note names two ways out: starch, which gets in the way physically, and citrate, which chelates the calcium.