I know this as "callu de cabreddu", but it's the same thing: https://guffantiformaggi.com/en/cheese/callu-de-crabettu/ https://guffantiformaggi.com/en/cheese/c

I know this as "callu de cabreddu", but it's the same thing: https://guffantiformaggi.com/en/cheese/callu-de-crabettu/ https://guffantiformaggi.com/en/cheese/callu-de-crabettu/ And it's anything but weird. It's likely that this is how cheese was originally discovered: in the fourth stomach (the abomasum, the "true stomach") of an unweaned ruminant slaughtered for food. The stomachs of unweaned ruminants are also the traditional source of rennet ("callu" means rennet and callu de cabreddu doubles as rennet). Why unweaned ruminants? Rennet is made of two proteolytic enzymes, chymosin and pepsin, that break apart milk proteins (specifically, caseins) by hydrolysis and cause them to coagulate and turn milk into curd. Chymosin has the strongest clotting power whereas pepsin has the strongest proteolytic power. Stronger proteolysis breaks proteins down into smaller peptides and amino acids and it turns out that those register to our sense of taste as bitterness. Chymosin has strong clotting power at a pH of 6.2 to 6.4, close to that of fresh milk (around 6.8), whereas pepsin clots milk best at a pH of 1.7 to 2.3 which is way too acidic for cheese and basically impossible to get with the usual way to acidify milk for cheesemaking, fermentation of lactose by Lactic Acid Bacteria. LAB generally don't develop at a pH below 4.6 so I don't think milk can even get to the ideal pH for pepsin just from fermentation (pepsin is probably fine-tuned for the very acidic environment of a mammal's stomach). So basically, to get the same clotting power with pepsin as with chymosin one would have to make a cheese so tangy and bitter that it would be inedible, if it could even be made in the first place. Now, the age thing. Both chymosin and pepsin are produced in the stomachs of ruminants, young and old, but younger animals produce more chymosin while older animals produce more pepsin. I think it's something like 75/25% chymosin/pepsin for unweaned animals and the opposite for adults, I don't remember. So, to have maximum milk clotting power with slower proteolysis, and less chance of developing bitter tastes, you need to use the rennet from a young animal, preferrably one that hasn't yet eaten grass. It appears that eating grass is what triggers the mechanisms that start producing more pepsin than chymosin. Don't ask me why because I have no idea.