What is Rennet?
Rennet is an enzyme used in the cheese making process to coagulate or set milk and allow cheese curds to form.Traditional Animal Rennet is an enzyme derived from the stomachs of calves, lambs, or goats before they consume anything but milk. Rennet used in cheese making is about 90% pure chymosin. Vegetable Rennet is an equivalent chymosin product which works equally well but is not animal derived. Vegetable Rennet can also be found in Tablet Form.
Rennet thrives at temperatures in the 85-105F range, but it won't be deactivated completely until it reaches the 140F's. Rennet continues working to set the milk as long as it has the right conditions. So, when a recipe calls for cutting the curds after a certain time period, it is important to follow the directions. Otherwise, your curds may be too firm for the cheese you are trying to make.