Cheese Cultures 101

A breakdown of the bacteria that makes cheeses unique.

Any serious cheese lover knows that cheese is created by adding a culture to milk. But what exactly is a culture? What does one look like and what does it actually do?

“At its core, a cheese culture is a specific strain or strains of lactic acid bacteria that are added to milk to facilitate the cheesemaking process,” says Devin Thorson, product development manager for cheese and eggs at Organic Valley, based in La Farge, WI. “I view the cheese cultures as the life of the cheese. They’re eating the lactose, which is the milk sugar, and converting that into lactic acid. That development of acid drops the pH, which aids the rennet in the coagulation of milk, which allows for the separation of curds and whey.” The two substances are often cooked together to help the curd set and develop the correct texture. Soon after, the whey is drained off so that only the curds, which form the cheese, are left behind.

Cheese cultures can be broken down by whether the bacteria are mesophilic or thermophilic. Mesophilic bacteria grow best in milk that is between 70 and 100 degrees F, says Dave Potter, president of These are commonly used for cheddar and many American cheeses, including Monterey jack. Thermophilic bacteria thrive in environments up to 125 degrees F. They are often used to make Swiss and Italian cheeses.

Cultures do much more than create cheese. “The other group of cultures includes adjunct or ripening cultures,” says Peter Dixon with Parish Hill Creamery, Putney, VT, which makes seasonal rawmilk cheeses. “There are a wide variety of microbes—not just bacteria but also yeasts and molds—that can affect the interior of a cheese, including its texture, but also the rind.”

The combination of cultures can add nuances to the flavor and encourage the development of physical attributes, including crunchy whey crystals and the cheese’s overall structure. “We put a special bacteria in with Swiss that causes the eyes,” says Robin Frojen, a professional faculty member at the Arbuthnot Dairy Center at Oregon State University in Corvallis and the creamery and cheese plant manager for Beaver Classic cheese.

To some extent, making different types of cheese is less about what bacteria are used and more about how the cheese is made. “With culture, time and temperature, at the moment, we can create 33,000 types of cheese—just by fiddling with that combination,” says Frojen. “We can use the same time and temperature, but if we use a different culture, that can be the difference between a dense, hard Alpine cheese versus a holey Swiss.”

These helpful bacteria also play a role as natural preservatives. “One benefit of cultures is that they create a competitive environment within the cheese, which helps preserve the cheese by slowing the growth of spoilage bacteria,” says Thorson. “Otherwise, cheese is a great place for bacteria to thrive. Having a set amount of good bacteria will help prevent spoilage and unwanted flavors from developing.”

Commercial and Homemade Cultures

Cheese cultures come in three basic forms: freeze dried, frozen and, less com­-monly, liquid form. “Most cultures will come from culture houses, and that’s what they do: they create cultures and multiply them in the gazillions and sell them,” says Frojen.

But it’s worth noting that commercial cheese cultures aren’t necessary for making cheese. Some very large companies (and even a few small, artisan firms) may have an in-house team that nurtures the perfect mix of cultures for their product. “The concept of starter cultures for cheese grew out of a modernization and the industrialization of cheesemaking,” says Dixon. Historically, farmers made cheese the same day they collected the milk. Refrigeration gave cheesemakers a break because they could keep the milk cold until they had time to process it, but milk that’s kept in cold storage, even overnight, loses enough of its natural lactic acid bacteria that more were needed to get the cheesemaking process started.

“Once we got the pasteurization, there were no bacteria left in the milk to make lactic acid,” says Dixon. People could still do direct acidification and make cheeses like mozzarella, “but anything that was meant to be aged had to use a starter culture.”

Although most American companies and home cheesemakers purchase selected-strain, laboratory isolated starter cultures, it is possible to make starters using fermented whey or clabbered milk. This yogurt-like substance must be frozen or, similar to sourdough starter, maintained and used with regularity.

“The advantage to doing this is that you can claim the closest link to terroir, or the taste of your place, because you’re not using anything away from your locale,” says Dixon, who notes that information about the process for making these starters has become much more accessible in recent years. “The culture is made directly from the milk itself and is raw.”

Many cheesemakers in other countries are still crafting cheeses using their own starter cultures, which is a good thing, Dixon says. “We’ve gotten to the point where organizations like Slow Food feel like we’re in danger of losing the diversity of microbes in cheese. As more traditional cheeses are industrialized, we’re losing the microbes that are indigenous to those particular regions.” Not only does that limit the microbiological diversity of the foods humans ingest, losing this important element of terroir in a region could mean eliminating the flavors and textures people are accustomed to finding in certain cheeses. This is something that can never be approximated by processing.

Using Cheese Cultures

Those venturing into cheesemaking for the first time should keep a few things in mind when using cultures. “Storage is important,” says Thorson. The cultures will come frozen, and they should stay that way until they’re ready to be used. “At room temperature, the bacteria will grow and maybe grow out of control, and then the acid development will happen too fast, so the desired flavor and texture won’t develop.”

In addition to using high-quality fresh or properly-stored cultures, Frojen recommends buying the least-processed milk available. Pasteurized milk is fine, but products labeled “ultra-pasteurized” or “ultra-filtered” will more frequently result in a cheesemaking failure.

It’s important to follow the recipe that comes with a culture from a commercial outlet, or order the specific culture that a recipe calls for, Potter says. Various suppliers may offer similar types of culture, but the concentration or package size will be different.

“Most of the cheese cultures that are available are already pre-blended and have recommended usages for different types of cheese,” he says. “Someone once told me the culture is the orchestra and you’re the conductor, and you’re the one controlling what they play based on the recipe. If you cook the mixture hotter or faster, it changes the profile of the cheese.” It’s best to stick to the score until you get more experience.

But once you have a better understanding of the cheesemaking process, the sky’s the limit. “I implore my students to play, and that’s how we end up with some of our best cheese,” says Frojen. While she agrees that it’s a good idea to follow a recipe at first, the next time you make that cheese, “if there’s something in that cheese that didn’t speak to you, or it wasn’t the flavor you were hoping for or the texture was different, try again. The more you do something, the more you’ll feel at home with it.” She points out that the American Cheese Society’s American Original category has really taken off, and that every year there are new cheeses in competitions. Careful experimentation with new cheese cultures can result in novel products that people will love for years to come.  

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