The roots of the term rennet come from rennet derived from animal parts, but in cheesemaking, with modern manufacturing the term is now used broadly to describe a range of chymosin and pepsin based coagulants. This general rennet article discusses formats, storage, amount, and preparation; specific rennet types, their formats and concentrations are in the Rennet Types, A To Z article.
Rennet through the ages has been made from the abomasum or fourth stomach, in young un-weaned milk fed calves and contains the rennet enzymes chymosin and pepsin. Due to high cost of manufacture and as calf based rennet does not qualify for some diets and may concern some for animal welfare reasons, starting in the 1990’s other forms of coagulants were manufactured.
Rennet normally is manufactured and available in a liquid, paste, and powder formats with liquid being the most common by far.
Most calf based based rennet manufactures recommend:
- For liquid calves rennet, store at temperature below 3-7C / 38-45F, i.e. in household fridge, not in normally warmer cheese cave. Store away from direct sunlight to preserve maximum activity (ultra-violet rays in sunlight destroy the rennet activity). Product’s strength will decline at 0.5% per month if ideal storage is followed for all times between manufacture and use.
- For powdered calves rennet, store at 38 to 45°F in closed container away from sunlight. This can give high, greater than 1 year shelf life.
As rennet can come in different strengths, any specified amount of rennet in a cheese making procedure should be ignored and the amount of rennet used per volume of milk based initially on the manufacturer’s directions. These directions can be found either on the product’s container or from their website (many of these files are posted in CheeseForum.org’s Library in the Forum). This amount should be increased or decreased with the users experience and results with the type of milk they are using.
- Rennet degrades based on age and storage best practices, adjust as appropriate.
- In general, store bought manufactured pasteurized and homogenized milk is requires more rennet than raw milk.
- For single strength liquid calves rennet, dilute in cool un-chlorinated water at ratio of 15-20 parts water to 1 part rennet by volume.
- For powdered calves rennet, dissolve in 400 times it’s weight of non-chlorinated cool water, let sit for 30 minutes with occasional agitation for complete dissolution.