Archives Straight from the Vat!

January/February 2008

The Importance of Knowing Your Rennet

Some labels read simply “rennet”. Others say “enzymes”, or “vegetarian friendly coagulant”, or “vegetarian rennet”, “microbial enzymes”, “vegetable rennet”, occasionally “chymosin” and yes, you will even see the words “rennet free” (on a hard cheese!). 

If one is going to truly appreciate cheese, one also needs to know something about each of its simple ingredients for each plays an enormous role in the final taste, texture, moisture level and aroma profile of the cheese.  And this means it is important to know something about rennet or more generically, coagulating agents.

Coagulants Used in Cheese Making

A coagulant is anything that curdles milk.  Rennet is a generally used as a generic term used to describe a an animal dervived coagulant that includes the enzyme rennin or chymosin (the two terms refer to the same thing—-rennin is an older term while chymosin is the more chemically specific term for the same enzyme).  But rennet is only one of several types of coagulating agents.

Essentially there are 5 types of coagulants used to make cheese:

1. Animal Derived Rennet: This the rennet used in most traditional cheese making plants. The rennet or rennin refers to collection of enzymes that comes from the fourth stomach of ruminant animals (kid, calf or lamb). If we look at rennet through a chemist’s eyes, rennet is chiefly made up of two enzymes that break down protein chains in milk: chymosin and pepsin. The enzyme mostly responsible for coagulating milk is chymosin as it works to breakdown casein—the primary protein of concern to cheesemakers.  As chymosin is the chief coagulating agent, today we see highly clarified versions of animal rennets which contain up to 97% chymosin—an outcome considered to be desirable by some cheese makers hoping to achieve a very clean taste profile and quick set.  In addition, there are now also organic animal rennets on the market.  Animal rennet in any form is still the most expensive coagulant (Up to 2x more expensive than alternatives) on the market.  It’s price is a function of supply which in turn is tied to events on the global market for cow, goat and lamb meat products.  Some perceive the use of animal stomachs to produce rennet naturally as somewhat primitive. Others perceive it as an example of how to ensure we make use of all parts of an animal.

2. Microbial Rennet: Microbial rennet is term used to describe a coagulating agent produced by a specific type of mold, fungus or yeast organism grown and fermented in a lab setting.  This coagulant is considered vegetarian friendly as the enzyme produced by the organism is not derived from an animal. While this type of rennet is appropriate for vegetarians, cheese makers agree that cheeses made with this type of microbial rennet tends to result in bitterness in the flavor profile especially when the cheese is aged. This coagulant is less expensive than animal rennet.  But true microbial rennet is now hard to find.  Its use has been replace d by FPC Rennet.

3. FPC-Fermentation Produced Chymosin Rennet:  This is fairly new type of microbial rennet (1990). This version of microbial rennet is made by taking the rennin producing gene out of the animal cell’s DNA string and then inserting into the a bacteria, yeast or mold host cell’s DNA string. Once inserted, the newly placed gene initiates the production of the chymosin enzyme within the host.  The host culture is cultivated and fermented. The result. An inexpensive harvest of real chymosin enzymes.  This is seen to be an improvement on the original microbial rennet as it is real chymosin and not a mold or yeast based substitute. Moreover, it can be more economically produced in unlimited supply and addresses some of the concerns with pure microbial rennet regarding the bitter flavor in aged cheeses.  The procedure itself has been around for some time and is similar to the procedure used to make many vaccines.  But, there is more to consider.

FPC Rennet and GMO Controversy

FPC rennet is a GMO product. And, according to the culture companies, 90% of all cheeses produced in North America is made with FPC rennet. However,  ingredient labels do not distinquish between this type of microbial rennet or the original non-GMO based type.  And the fact that use of FPC type microbial rennet is not labeled a GMO product leaves those who oppose the use of GMOs in the dark when it comes to choosing their cheeses. 

In addition, further confusion and debate arises over the general differences between GMO products versus “genetically engineered” products as the latter elicits deeper concerns from those opposed to this type of science. While FPC rennet is GMO, it is not a genetically engineered product, technically speaking, because, the DNA taken from the animal cell and inserted into the DNA string of a bacterium or mold is not changed.  Genetically engineered foods actually goes as far as to modify the specific gene responsible for a particular function in order to improve its function.  In other words, it takes messing with genes to another, deeper level.  Its like playing with the shape of the lego block its self, not just with the order of the lego blocks.

In the end, what this means is that most cheese in North America is made from vegetarian friendly but still animal originated, GMO derived FPC rennet.  And that while use of this type of rennet is banned in GMO-free European countries doesn’t mean the cheese we buy from those countries are necessarily FPC free.  To quote one Danish expert “We can’t use FPC rennet in Denmark for our own domestic cheese or cheese make for other European countries which have banned its use.  We only use it for cheese we export to North America.  .”Why? Because again, it is a cheaper and more consistently available form of rennet. 

4. Vegetable Rennet:  True vegetable (vrs vegetarian rennet term which is used interchangeably with microbial rennet) rennet comes from plants which produce certain enzymes that have coagulating properties.  Some examples include cardoon thistle, fig tree bark or nettles.  These are “real” vegetable rennets. However, they often also have undesirable effects on cheese flavor (bitterness) and are a little more unpredictable when used in cheeses not traditionally made with vegetable rennet.  Still, some traditional Portuguese cheeses are still made with vegetable rennet as are cheeses in other countries where killing lets say, a calf,  would not be allowed or economically wise.  In North America, commercially produced vegetable rennet is hard if not impossible to source. However, some artisan cheese makers (e.g. in Maine) are experimenting with it once again and word has it that a company in Edmonton, Alberta will soon be commercially producing a true vegetable rennet.

5. Citric Acid or Vinegar:  Finally, some cheeses like Ricotta are coagulated using simple lemon juice or vinegar. However, this coagulant is mostly used when making a heat precipitated curd.  These coagulants are decidedly vegetarian.  But this coagulant has a very limited use due to its limitations and noticeable taste profile. 

To conclude, it is indeed important to know your rennets—especially if you are in cheese retailing or working in a restaurant offering cheese plates.  And it is worthwhile to ask your cheese makers to be clear about what type of rennet they use and why.  In my view the reason for asking is not to judge the choice. But instead to understand why that rennet type was chosen for that cheese and who they see as their target market.  Indeed the rennet a cheese maker chooses to use results in making difficult trade offs between three priorities: taste, texture and politics.  And you will serve your customers well if you can articulate what trade offs the cheese maker was willing to make and why. It is also important to help your customer make choices that are best aligned with his or her priorities.



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