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Food and Drink

Mystery ingredient

The enzymes that turn milk from liquid to solid have a storied history

Wendy M. Levy, a local cheesemonger, has been working with cheese since 1995.

BRATTLEBORO—Cheese is a food that has very few components, at least in its natural state. Provided you are not eating something like “processed cheese food product,” your cheese should contain only milk, rennet, cultures, and salt.

It’s safe to assume most people old enough to choose their own food know what milk and salt are, and “cultures” refer to beneficial bacteria used in the first step of cheesemaking (converting lactose to lactic acid).

But what of this mystery ingredient, rennet?

Rennets are enzymes that coagulate milk, turning the liquid into a solid mass: cheese curd. This cheese curd is then further manipulated to become cheese.

Without coagulation, there would be no cheese. You’d just have some milk that wouldn’t taste very good.

If left to its own devices, milk will eventually sour, and if you’ve ever been unlucky enough to have milk sour on you, you know it gets clumpy.

During the cheesemaking process, which can be described as the controlled spoilage of milk, the cheesemakers carefully steer the processes of souring (acidification) and clumping (precipitation or coagulation) to bring about the desired effect: delicious cheese.

Perhaps this chemical change is what inspired the late wordsmith Clifton Fadiman to declare cheese “milk’s leap toward immortality.”

* * *

Nearly all cheeses contain some form of rennet, but not all rennets are the same.

According to Dane Huebner, microbiologist, master cheesemaker and director of research and development at Windham County’s Grafton Village Cheese Company, it’s important to “stress the distinction between the various types of rennet, because there’s a lot of confusion.”

Vegetable-based rennets are the least utilized here in the United States; they are primarily found in Spanish and Portuguese sheep cheeses, as well as a scant few Italian sheep cheeses. The most common source of this type of rennet is the cardoon, a thistle-like plant that’s a relative to the artichoke.

Animal-based rennets are derived from the vells, or fourth stomachs, of ruminant animals. Generally, unweaned animals’ stomachs are used to harvest animal rennet, and the cheese world has used bovine calves, lambs, kids, and even camel calves for rennet.

Unweaned bovine calves have traditionally been the most popular source of animal rennet for two main reasons:

• Milking calves’ digestive enzymes offer a better flavor profile in the finished product (cheese) than those of adult cows, which tend to make a cheese bitter.

• Calf rennet was a byproduct of veal production. When veal was a more popular meat, more calf stomachs were available, thus promoting further use of the livestock resource for farmstead cheesemaking and a possible additional income stream for a livestock farmer, who could sell or trade the rennet.

During the 1970s, when activists drew attention to the processes and conditions under which veal was raised, the veal market dried up.

The noticeable decrease in the secondary market of veal-derived rennet drove prices up, often beyond the reach of most cheesemakers.

At the same time, during the prosperous post-World War II decades, more middle-class Americans were developing a more worldly palate, and they demanded more European cheeses.

With the increase in the demand on cheesemakers along with the price of a crucial component to cheesemaking, the cheese world needed a solution.

* * *

A modern fix came from an Old World player: Chr. Hansen, a Danish “global supplier of bio-science based ingredients to the food, health and animal feed industries,” as the company describes itself. The firm is one of the major global suppliers of rennet to the cheesemaking industry.

Because cheesemaking is so dependent on microbiology, even the slightest variation or deviation in the raw materials can adversely affect the finished product. Consequently, cheese made from traditional animal rennet varies widely.

In 1874, Chr. Hansen produced the first standardized animal rennet, enabling cheesemakers to produce a consistent product. The company’s commercially available animal rennet also freed the cheesemaker from having to harvest her own, which is labor intensive and requires slaughtering the animal, which might not be cost-effective for a livestock farmer.

Flash forward 100 years to the 1970s, when Chr. Hansen developed microbial coagulants to satisfy the industry’s need for a more affordable crucial cheesemaking component.

Hannilase is Chr. Hansen’s trade name for Rhizomucor miehei, a fungus that performs the same function as animal-based rennet, but is fully non-animal-derived.

This microbial enzyme has been a boon to cheesemakers.

According to Jim Wallace, technical expert at Deerfield, Mass.–based New England Cheesemaking Supply, “It is estimated that 70-80 percent of all cheese made in America is from non-animal derived rennet.”

In addition to affordability and abundant, consistent availability, Wallace says cheesemakers choose Rhizomucor miehei because it “produces a higher enzyme specificity that allows better control in large production processes. Also, despite the fact that milk is an animal-based product, some producers prefer a non-animal-based [rennet] for their customers.”

Dane Huebner says Grafton Village Cheese Company uses this type of rennet to make their cheeses because “we like the flavor profile it offers, the cheese appeals to vegetarians, and it fits in with our ‘no-GMO’ policy.”

An irony in the cheese world is that the actions of animal-rights activists contributed to the proliferation of rennet made from genetically modified organisms (GMOs).

In the 1980s, the science world began experimenting with gene recombinants, and a new type of rennet was introduced into the cheesemaking industry: fermentation-produced chymosin, or FPC.

According to, the website produced and maintained by Paul McSweeney, professor of food chemistry at University College in Cork, Ireland, FPCs are “nature-identical” to the rennet extracted from bovine calves.

FPCs are animal-derived; the enzyme harvested from the bovine calf is “produced by fermentation using a host organism such as [the fungus] Aspergillus niger,” according to Chr. Hansen’s website.

A rival company, Netherlands-based DSM Food Specialties, makes its product by fermenting the animal-based enzyme in the yeast Kluyveromyces lactis.

There are many benefits to using FPCs. Even though FPCs are more expensive than Rhizomucor miehei, their cost per use is lower, so a little goes a longer way. Because of their purity and their microbiological composition, the bitterness that can result from using other rennets is markedly decreased when FPCs are used; yield is also increased with the use of FPCs. FPCs are also certified as halal, kosher, and vegetarian.

What FCPs are not, however, is organic, according to the requirements of organic certification, because FPCs are derived from genetically modified organisms.

The producers of FPCs, as well as other industry supporters, attempt to quell the fears of the GMO-phobic public by assuring consumers that, while gene recombinants are used to produce FPCs, they are not a GMO product.

As McSweeney writes on his website, “Although FPCs are from the biotechnology industry and are expressed in genetically modified microorganisms (GMOs), it is important to remember that they are products of GMOs and do not contain any living genetically engineered organisms.”

“FPCs are thus in exactly the same category as human insulin, most of which is now produced by a similar approach to FPCs and which diabetics inject directly into their bloodstream,” McSweeney continues.

It also worth noting that very little rennet, regardless of the source, is left in the finished cheese. In a 1-kilogram (2.2-pound) cheese, about 0.0003 grams of rennet remain.

Very little rennet is required to coagulate the milk: about 1 gram of rennet can precipitate approximately 15 kilograms of milk, (and is said to have a potency of 1:15,000). In addition, a great deal of the rennet is washed away when the whey — the liquid byproduct — is drained from the curds.

Additionally, cheeses precipitated using FPCs are legal for production and sale in the European Union, and the EU is considered to have the most stringent GMO regulations in the world.

The European Food Safety Authority (EFSA) subjects all GMO foods and food components and additives to extensive evaluations and trials, and that agency has declared FPCs acceptable.

* * *

Despite these assurances, some consumers and cheesemakers (like Grafton Village) prefer to avoid cheeses made using FPCs.

It is unclear whether the state of Vermont will consider cheeses made with FPCs as containing genetically modified organisms, thus requiring their labeling, when the “GMO labeling bill” goes into effect in 2016. (At this writing, the bill has been passed by both the House and Senate and will presumably be signed by Gov. Peter Shumlin.)

Cheese labels currently do not offer the consumer much information on which rennet is used in production. Some labels guarantee the cheese as being “suitable for vegetarians,” which means that the only rennet not used is animal-based; FCPs, which are derived from animal sources, are allowed. If a cheese is certified organic, the rennet can be animal-based, Rhizomucor miehei-based, or vegetable-based (likely, cardoon).

If a consumer is purchasing cheese directly from a cheesemonger, as in “cut to order,” or if you can find a cheesemonger staffing a self-service cheese case, it is worth asking the cheesemonger which rennet was used.

Results might vary, though, because sometimes that information is not made readily available. But a reputable cheese shop with good customer service will work to find that answer.

It is always worth asking.

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Originally published in The Commons issue #253 (Wednesday, May 7, 2014). This story appeared on page C1.

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