The purest rennet comes from the inner mucosa of the fourth stomach of unweaned baby cows, thereby requiring cheesemakers to have strong relationships with the veal industry. The calves surrender their stomachs to men who dry, clean, and cut them into tiny pieces, which are then salted with wine and whey and filtered overnight. One gram of the final concoction is enough to coagulate four liters of milk. (Thank you, baby cows!)