Cheesemaking Ingredients: Acid, Cultures, Rennet, Water, Mold and Yeast, Salt

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Acidification is one of the underlying processes in cheesemaking. As the milk or cheese acidifies (or cultures), it becomes tangy or tart, and the texture changes as a result. Part of what you are controlling with the timing of your cheesemaking is the rate of acidification: Acidify your curd too fast, and it can become grainy or brittle; acidify too slowly, and your pleasantly tangy flavor may turn full-on sour. To jump-start the acidification of milk for cheese, we often add lactic acid-producing bacteria or a pure form of acid directly to the milk.

When I teach tasting classes I like to describe the acidity of a cheese (or a wine, or a beer, or a chocolate, etc.) as the skeleton of the product. I think of it this way: Acidity provides the structure of the thing, which the producer can then adorn with flavor through different techniques and additions, as they see fit.

Here are a few of the acidification “vehicles” you will use to prepare cheese:

Lemon juice is the most recognizable acid. We will use it to coagulate the curd when making Ricotta.

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Citric acid (sometimes called “sour salt”) is a weak acid naturally found in citrus fruits. In cheesemaking it is most often used to make Mozzarella.

White vinegar can be used to make ricotta, but I have an aversion to using something with such an intense aroma to make such a delicate cheese. Use white vinegar when making Queso Fresco.

Bacteria cultures, most of which include various strains of lactic acid–producing bacteria, are used for most cheesemaking recipes. As the bacteria are activated in the milk and cheese, they convert the milk sugars (lactose) into lactic acid. This conversion process increases the acidity of the milk/cheese.

Rejuvelac is a tart, tangy liquid by-product of soaking grains. It acts on the nuts in a similar way to vinegar, adding acid itself and fostering the development of more acid as the nuts ferment.

A recognizable example of unwanted acidification of milk: when you forget about that half-full quart of milk in the refrigerator and open it up a few weeks after its sell-by date. The indigenous bacteria in the milk are still very slowly at work when the milk is in your refrigerator, and the result of their long-term efforts is the soured, curdled mess you now have to flush down the toilet.


Cultures of bacteria are added to milk to acidify it in the process of cheesemaking. Using starter culture to acidify milk is called ripening. You can get starter cultures and secondary cultures at your local specialty cheese shop or homebrew supply shop if you have one, or from  cheesemaker friends, or from online shops.

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As mentioned in the last section, one function of a starter culture is to acidify the milk by converting lactose into lactic acid. The type, quality, and even the safety of cheese are defined by the starter culture. Different starter cultures are chosen depending on the cheese being made; cultures are chosen for their flavor-producing qualities and their ability to withstand higher or lower temperatures. In addition to acidifying the milk and protecting against harmful bacteria, starter cultures also contribute to the final flavor of the cheese.

Thermophilic cultures are used when cheesemaking involves cooking or heating the curd to higher temperatures (around 120 degrees Fahrenheit), usually in the case of harder, longer-aged cheeses.

Mesophilic cultures are used for softer, younger cheeses that do not require the curd to be heated as high. Flora Danica is a specific mesophilic culture that is often called for in recipes because of its ability to add a distinctly buttery taste to cheese.


Sometimes referred to as ripening cultures, secondary cultures are added to the cheesemaking process to perform specific, often specialized tasks. One culture (Propionibacterium freudenreichii ssp. shermanii) produces the eyes in Swiss-style cheese; another (Penicillium roqueforti) causes blue cheese to develop a biting, piquant flavor.

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Rennet is an enzyme used to coagulate milk. A cheesemonger at the famed Murray’s Cheese Shop once explained it to me as acting like a light switch. Before adding rennet you have milk, in which solids are suspended in water, repelling one another (hence the milky look of milk). Add rennet and you have flipped the switch: Suddenly the milk solids are attracted to one another and come together, forming a curd. Rennet is sold at many culinary shops, homebrew supply stores, and specialty grocery stores. There are three commonly used types of rennet:

Animal rennet was originally sourced (in most cheesemaking traditions) as a by-product of the butchering process, since a coagulation-causing enzyme happens to be found in the stomach lining of a calf, lamb, or kid. Today many cheesemakers still use traditional rennet, but more often than not it is purchased through a large-scale culture house and no longer procured from the butcher down the road.

Microbial rennet is a laboratory-made enzyme, crafted to behave like traditional animal rennet. Many cheeses labeled vegetarian are made using this rennet.

Vegetable rennet is a coagulation-causing enzyme derived from vegetables. Thistle rennet is historically the most common and still widely used today in Portugal to make Torta-style sheep’s milk cheeses.


Though the cheesemaking process is a great big exercise in separating the water from the solids in milk, we do need to add water from time to time. Most often water is added as a dilution vehicle for rennet, calcium chloride, or lipase, and we also add water to make Gouda-style washed-curd cheeses. When water is called for, follow the same rule as you do for your milk: You want the purest, least adulterated version. That means natural non-chlorinated spring water, which in my case at least I have to buy from the corner bodega. Tap water is equivalent to homogenized milk: Do not use it for cheesemaking!

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Molds and yeasts are both types of fungus, and they are all around us. In cheesemaking, molds such as Geotrichum candidum and Penicillium camemberti are added to the makes for Brie and Camembert, which are both mold-ripened and soft-ripened cheeses. Penicillium roqueforti is a mold added to milk to produce the signature “blue” in blue cheese.

Molds need oxygen to grow, so they either proliferate on the outside of the cheese — creating, for example, the signature white mold rind on a Brie-style cheese — or they grow inside the cheese, enabled by the piercing we do to blue cheese wheels when they are young. 

Yeasts can be added to the wash on a washedrind cheese to keep the acidity of that type of rind environment low. In other types of cheese, yeasts are not actively incorporated, as they tend to cause bitter flavors.

I was taught to love and admire fungi (specifically Geotrichum candidum) by my friend the microbiologist Sister Noella Marcellino, aka the Cheese Nun. Her work on microbes has  influenced cheesemakers and dairy scientists around the world and set lawmakers and governmental regulators straight about the safety of naturally fermented foods.


In cheesemaking you should follow the same rulefor salt as you do for water and milk: Unadulterated is best, so be sure to use non-iodized salt when making cheese. I find fine, granular salt to be difficult to spread evenly on a cheese surface, so I suggest using a coarse non-iodized salt.

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What to Do with Leftover Whey

To get the most value out of your cheesemaking, try not to discard any by-product of the process. The main by-product of cheesemaking is whey, so if you can find ways to use your whey you will get much more distance from your make. Here are some ideas for how you can use this nutrient-rich by-product:

  • Use whey instead of water in BREAD OR DOUGH recipes, especially sourdough.
  • Soak dried BEANS AND LEGUMES in whey before use, to impart added nutrients.
  • Flavor the whey with macerated fruit and mix with equal part seltzer for a REFRESHING SPRITZER.
  • Start with whey as a base for SMOOTHIES AND SHAKES of any kind.
  • Substitute whey for water when cooking RICE.

Also from The Beginner’s Guide to Cheesemaking:

The Beginner’s Guide to Cheese Making is an ideal introduction to making cheese at home. Filled with simple advice and straightforward recipes, this book makes it easy for you to start crafting your own scrumptious cheeses. No experience needed. Want to customize your cheeses? Discover the best ways to experiment with recipes and change up your creations. You’ll also find suggestions for the best beer and wine pairings. Learn how your homemade cheese can become the essential ingredient in savory snack, meal, and dessert recipes. Become the cheese master (who never has to settle for store-bought) with The Beginner’s Guide to Cheese Making.

Reprinted with permission from The Beginner’s Guide to Cheesemaking by Elena R. Santogade and published by Rockridge Press, 2017. 

Published on Jul 9, 2019


Inspiration for edible alchemy.