Hi Anthony, I checked with our lead cheesemaker, Helen Cowan, and here's her response:
"Rennet is often listed as “enzymes” on the ingredient label, so it can be hard to tell whether or not a cheese is vegetarian or not. Occasionally, like with our cheddar, it is listed as “calf rennet” or “veal rennet,” in which case the cheese is not vegetarian. Rennet is added directly to the milk in order to coagulate the milk into curds, and the final product does contain a small amount of rennet (and when I say small, I mean small! We use about 150 mL -- about 5 oz -- to coagulate 5000+ lbs of milk!) That leftover rennet actually helps age the cheese, which is why we prefer to use the more complex calf rennet instead of cultured enzymes.