Animal vs Vegetable Rennet: Which Should You Buy?

A six-month line divides them — your ageing plan decides.

The verdict

Animal (calf) rennet, about 90% chymosin, is the retailer-endorsed choice for longer-aged cheese because its residual components finish the protein breakdown cleanly. Microbial ('vegetable') rennet from Mucor miehei is a true chymosin equivalent and the vegetarian standard — with one documented caveat: it can turn slightly bitter in cheeses aged past about six months. So the rule is your calendar: fresh and short-aged cheeses, either works (choose by diet); wheels you plan to age past six months, choose calf rennet or fermentation-produced chymosin (FPC), which sidesteps both issues and is often sold double-strength.