Farmstead Cheeses and Wines: Jeff’s Blog

We often get asked about Rennet.  Rennet is an oft-misused word for the method of separating milk into curds and whey, allowing for the production of cheese.

Presumably, the first cheese was produced by accident when the ancients stored milk in a bag made from the stomach of a young goat, sheep or cow.  They found that the day-old milk would curdle in the bag (stomach), yielding solid chunks (curds) and liquid (whey).  Once they discovered that the curd-chunks could be separated out and dried, they had discovered a means by which milk, an extremely perishable food, could be preserved for later use. The addition of salt was found to preserve these dried curds for long periods of time – the first cheese!

At some point, someone discovered that the most active portion of the young animal’s stomach to cause curdling was the abomasum, the last of the four chambers of the stomach of a ruminant animal.  In particular, the abomasum from a suckling kid or calf was especially active.  The abomasum was cut it into strips, salted and dried.  A small piece would be added to milk in order to turn it into curds and whey. At some point, the Germans began calling this material rennen, meaning to run together, or to coagulate. The technical term for rennin is chymosin. 

Vegetarians often ask us about the type of rennet used in the cheeses we sell.  Traditional rennet, or animal rennet is still made from the stomachs of young animals culled from the herd.  Traditional cheesemakers, such as the ones associated with Neal’s Yard Dairy, feel that Traditional rennet makes for a better cheese, especially with cheeses that age longer, and imparts the cheese with a slightly fluffier and softer texture. 

There are several ways to coagulate cheese that don’t involve natural rennet.  Some plants, such as thistle, have a coagulant property that can be used in cheesemaking.  Some molds, such as Rhizomucor miehei are able to produce enzymes. These molds are produced in a fermenter and then concentrated and purified to avoid contamination.

The flavor and taste of cheeses produced with microbial rennets can tend towards bitterness, especially after longer maturation periods, but are fine for most  younger cheeses.  These so-called microbial rennets are suitable for vegetarians..

These days, chymosin can be produced by genetically engineered bacteria into which the gene for this enzyme has been inserted.  When the bacteria are grown in large vats, they secrete rennin, and it’s then purified for cheese making.    

The so-called GM rennets are suitable for vegetarians if there was no animal based alimentation used during the production in the fermenter — but only for vegetarians who are not opposed to GM-derived foods.

Whenever we know the rennet source on a cheese – traditional, vegetable, microbial, or GM, we notate it on the cheese.  Given the increased production cost of Traditional rennet, it’s best to assume that when it doesn’t specify the type of rennet used on the label of the cheese, the cheese is suitable for vegetarians.