Rennet is the enzyme that turns milk into cheese. Without it, milk doesn’t coagulate and cheese can’t form. Traditionally, rennet came from calf stomachs and was used that way for centuries. I still use veal calf rennet in my cheesemaking. Today, most cheese made in the U.S. uses FPC (fermentation-produced chymosin) instead. FPC is made with CRSPR tech by inserting the gene that produces chymosin into microorganisms (like yeast or fungi). Those microbes are then fermented, and the enzyme is puri