Rennet…The Key to Cheese Making

Hello Cheese Enthusiast!

Chymosin Image courtesy of Wikipedia

The subject of  rennet is one that I have wanted to share for some time…Why?...Well, when I got my first job behind a cheese counter, my boss Randy told me it would be one of the first (and most consistent) questions that I would be asked while working behind the counter (other than ‘Can I freeze cheese?’) 

He spent the rest of the morning trying to explain what rennet was, why is was important in cheese making, and more importantly which cheeses contained animal rennet. While he did the best job he could, I learned over the years that there was much more to the story than he shared. Cheese education and research was difficult back then, as there were only a few books out on the market (mostly for home cheese making) and the internet was years away from becoming a reality.

Image courtesy of The Catalog of Good Deeds

The humble beginnings of the rennet story have been told time and time again and I think that it is worthy of repeating here. This story took place in the Middle East where a young man was planning on taking a trip across the dessert. He packed with him all of the provisions that he would need like food, and of course, something to drink. Halfway through his journey, he stopped at an oasis to enjoy some of the fresh goat’s milk that he was carrying in his wineskin bag (these bags were traditionally lined with goat stomachs and were treated with tree sap, or other resins, to prevent liquids from seeping through). When he went to pour the contents into a cup, instead of fresh milk pouring out, a watery liquid (whey) poured out, but still feeling like there was something in the bag, he squeezed it and to his surprise, fresh cheese (curd) came out. So what happened here??....Well, you start with the fresh milk, poured into a bag made from the stomach of a young goat. It was the heat, rocking motion of the camel, and time that helped the natural enzyme, chymosin (a natural coagulant – See image at Top) release from the lining of the stomach and curdle the milk. Chymosin is the key component of Rennet.

Please keep in mind that this mythical story took place quite some time ago…In fact the oldest record of cheese making is from some pottery fragments that date from 7,000 years ago (5,200 to 4,900 B.C.). But that being said, there is probably some truth to it since goats have been domesticated for at least 10,000 years as they are small and manageable, will eat just about anything, and a great source of milk, meat, and pelts.

So, now that we know how rennet was discovered, let’s talk about its current application in modern cheese making:

Animal Rennet – Milk from Cows, Goats, and Sheep are the primary animal milks used in cheese making. So if the cheesemaker decides to use animal rennet, then calf, kid, or lamb rennet is used in this process. In addition to being mammals, Cows, Goats, and Sheep are also Ruminants. Ruminants are mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach known as the Abomasum, (prior to digestion). It is here where the Chymosin enzyme can be found. Without this natural coagulant in their young systems, these important nutrients would simply pass right through the animal. This enzyme naturally dissipates as the animal gets older. Don’t worry, no animal is killed for this enzyme, it is collected as part of the byproducts of the meat industry. So which cheeses still use animal rennet?...These would be your heritage cheeses that have been made for centuries across Europe, such as Emmentaler, Gruyere, and Comté.

“Because of the limited availability of these stomachs for rennet production, cheese makers have sought other ways to coagulate milk since at least Roman times”. Here are a few of them:

Microbial Rennet – “Some molds such as Rhizomucor miehei are able to produce proteolytic enzymes (an enzyme that breaks down proteins). These molds are produced in a fermenter and then specially concentrated and purified to avoid contamination with the unpleasant byproducts of the mold growth. The traditional view is that these coagulants result in bitterness and low yield in cheese, especially when aged for a long time.” 

Fermentation-produced chymosin – “Because of some of the inherent problems and imperfections of microbial and animal rennet, many producers sought other replacements of rennet. With genetic engineering it became possible to isolate rennet genes from animals and introduce them into certain bacteria, fungi, or yeasts to make them produce chymosin during fermentation. The genetically modified microorganism is killed after fermentation and chymosin is isolated from the fermentation broth, so that the fermentation-produced chymosin (FPC) used by cheese producers does not contain a GMO or any GMO DNA. FPC is identical to chymosin made by an animal, but is produced in a more efficient way. FPC products have been on the market since 1990 and, because the quantity needed per unit of milk can be standardized, are commercially viable alternatives to crude animal or plant rennets, as well as generally preferred to them. FPC was the first artificially-produced enzyme to be registered and allowed by the US Food and Drug Administration. In 1999, about 60% of US hard cheeses were made with FPC, and it has up to 80% of the global market share for rennet.”

“Cheeses produced with FPC can be certified kosher and halal, and are suitable for vegetarians if no animal-based alimentation was used during the chymosin production in the fermenter.” 

Vegetable Rennet – But before there was a Microbial alternative to Animal Rennet, it was plant based, or ‘vegetable’ rennet that has been around the longest. This alternative rennet was mentioned in Homer’s Iliad (written between 1,260 B.C. to 1,180 B.C.) where the Greek’s used extract of fig juice to coagulate milk. Other early common plants were Ground Ivy, Stinging Nettle (Urtica dioica) and Bull Thistle (cirsium vulgare). These are not nearly as common and do not produce a tight-knit curd (firm) the way that an animal, microbial, or FPC rennet would. 

If trying your hand at home cheese making, the New England Cheese Making Supply Co. is an excellent resource for all types of rennet, or you can even try your hand at making Nettle Rennet, or Thistle Rennet at home with these handy links.

As Paul Harvey would say…”and now you know the rest of the story”

Until next week…

Trevor