Wild Dairy Fermentation

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Peter Dixon (pictured at top) and Rachel Fritz Schaal share the title of head cheesemaker at Parish Hill Creamery, where they’ve been propagating cultures from raw milk since 2013. Photo by @parishhillcreamery

Long before packets of freeze-dried cultures for milk existed, there were dairy ferments. Cheese, yogurt, and kefir are probably second only to beer in the pantheon of fermented foods. However, in the modern world, 100 percent wild fermentation in dairy products is rare. There are many cheeses made from raw milk, though, and the fermentation of these is a joint effort between wild microbes and cultivated bacteria. Cheesemakers who use this approach rely heavily on wild microbes to produce a superior, nuanced cheese, but hedge their bets for optimal acidification and flavor by adding a pinch of commercial cultures. For those who want to play on the wild side, a deeper understanding of the concerns and the process is necessary.

Understanding Milk

One of the most important truisms I teach about milk is that it isn’t meant to see the light of day. Quite literally, nature only intended milk for immediate consumption by baby mammals for immediate acidification and coagulation in their tummies. Therefore, anything we do that attempts to extend the life of fluid milk — from refrigeration to storage and transportation — will alter the quality of milk. In a perfect world, a cheesemaker would milk their animals and use that fresh, warm milk to make cheese immediately. Though some are able to do that, the reality for most cheesemakers includes several other steps. Most home cheesemakers start with milk that’s been refrigerated, and therefore already altered.

Photo by Gianaclis Caldwell

In the mammary gland, milk is usually sterile (except in conditions of infection, and possibly some natural transmission from the mother). When milk is collected using a milking machine or by hand, milking microbes are also collected from the teat skin and the air. In clean conditions, these are mostly harmless — even helpful — microbes. But not always. Picture the microbe-packed dust particles moving with every step the cow takes, every swish of the goat’s tail, and every stomp of the ewe’s hoof. These particles all enter the milk. Even when harmless from the standpoint of food safety, they might interfere with proper fermentation.

Photo by Gianaclis Caldwell

Cultivating the Wild Side

I like to think of the teat surface as a garden from which wonderful microbes can be collected. This collection can’t happen without paradigm shifts away from the extensive udder sanitation that’s practiced on most modern dairies. But wait, didn’t I just warn you about all of the spores floating around? How can reducing sanitation help?

Photo by @parishhillcreamery

Conventional practices for proper teat and udder sanitation consist of cleaning the udder, sanitizing the teat, squirting out a few streams of milk, and then drying the teat. After milking, the teats are sanitized again to protect them from bacteria in the environment. This process can make for some very clean milk. So clean, in fact, that it won’t ferment naturally. Cows that live a healthy lifestyle — grazing in open pastures and nursing their young — grow lactic acid bacteria on their skin that naturally protects the udder from infection. The same thing occurs on our skin, unless it’s exposed to an excess of hand sanitizer or other chemicals that destroy the native flora. Changing this approach requires thought, timing, and verification that it’s benefited the animal’s health as well as the fermentation process. Reducing the use of harsh chemicals and providing clean living conditions are the basis for supporting the ideal teat microbes.

Photo by Gianaclis Caldwell

The cultivation of helpful microbes on the animal’s skin is a practice that’s better understood and implemented in Europe, where many traditional cheeses are made according to age-old methods. In those countries, scientists have researched how to collect the best microbes, rather than how to kill all of the microbes. Such a paradigm shift is difficult for most North American dairy scientists and inspectors to embrace. It’s a process of educating and learning from three perspectives: the farmer’s, the academic’s, and the regulator’s. Two books include much of the research done on this topic: Cheese and Microbes, edited by Catherine Donnelly, and The Microbiology of Raw Milk, translated by Bronwen Percival.

Acidification in Dairy

Unlike wild vegetable fermentation, dairy ferments can’t have salt added to them until after fermentation is complete. The bacteria that ferment milk are salt-sensitive and can’t do their jobs if the milk is too briny. Thanks primarily to the salt content, vegetable ferments are relatively risk-free, but dairy can be trickier.

Photo by @parishhillcreamery

In dairy products, the lactic acid bacteria, whether wild or commercially produced, convert the complex sugar lactose into simpler glucose and galactose. They then process these simple sugars further to produce acid and, sometimes, carbon dioxide, as well as other compounds. When this process happens over a 12-to-24-hour period, the lactic acid bacteria, as well as the acid they produce, should overrun any present pathogens. Many lactic acid bacteria also have a direct antimicrobial effect on pathogens. However, other fast-growing acid producers must also be monitored, namely bacteria from the coliform family. Without sending samples to a lab, it’s difficult to know which microbes are growing and fermenting the milk.

Assessing a Mother Culture

The lacto-fermentation test is a well-studied and documented method used by cheesemakers around the world to assess their milk quality — whether or not they add commercial cultures! Incubation temperatures range from 72 to 95 degrees Fahrenheit, with a goal time of no more than 24 hours for curd formation. Maintain an even temperature throughout the process, and use a sterile jar. After you incubate fresh, raw milk, assess the cheese for proper and timely curd formation, and then for flavor.

Photo by @parishhillcreamery 

If the milk is suitable for making a mother culture, a yogurt-like curd with a thin layer of whey will appear on the surface. The milk will also develop a pH of about 4.6 within 24 hours. If the milk is still liquid after 24 hours, then it has too little native bacteria, or may have been mixed with sanitizer or antibiotic residue. If the jar contains mostly whey, with a wad of thick curd at the very bottom, there are likely high counts of coliform microbes. After obtaining the optimal curd results, you can decide whether the curd has the aesthetic qualities you desire.

Always use raw milk from animals free of zoonotic diseases (any diseases that can be passed from animals to humans). Milk that has disease-causing microbes will still ferment normally, but could be hazardous to your health.

Photo by @parishhillcreamery

We’ve used lacto-fermentation regularly at Pholia Farm when making our commercial cheeses. I find it amazingly informative to the daily practices of the farm, as well as to my cheese-making. I also employ it during the classes I teach. It’s a method well worth using when making cheeses at home. The practice will help you more deeply understand and troubleshoot fermentation and issues with a mother culture. Making raw milk cheese gives you a chance to observe environmental microbes and natural milk systems at work in cheese-making, and the complex relationship these microbes share with those that exist in a raw milk source.

Modern Makers Using Ancient Methods

One of my first in-person instructors was the inimitable Peter Dixon, now one of two head cheesemakers at Parish Hill Creamery in Putney, Vermont. Peter, who has an academic background in dairy science, as well as almost 40 years of commercial cheese-making experience and 25 years of teaching, is a proponent of wild fermentation. Peter produces award-winning cheeses using the wild fermentation of milk from four special cows: Helga, Abigail, Clothilde, and Sonia. If you can get your hands on a wedge of Parish Hill cheese, you’ll be amazed!

Another early influence of mine was Rona Sullivan of Sullivan’s Pond Farm in Virginia. She made naturally coagulated cheese, using an approach she calls “bonnyclabber” (literally “good curd”), mimicking the historical cheeses made from a similar process by Scotch-Irish settlers in the region. 

Gianaclis Caldwell is the author of many books focusing on dairy products and small dairy businesses, including The Small-Scale Dairy. She practices her passions for farming, writing, teaching, and fermenting at her family’s off-grid Pholia Farm, in Oregon’s beautiful Rogue Valley. Find her on Facebook @Gianaclis and on Instagram @Gianaclis and @PholiaFarm.


Mastering Artisan Cheesemaking covers the intricacies of the science behind how milk becomes cheese. In easy-to-understand detail, it explores the complexity of fermentation, affinage (aging), and considerations for preparing each category of cheese variety. Enjoy thorough explanations of the craft and techniques that allow milk to be transformed into epicurean masterpieces. This title is available in our store or by calling 800-978-7464. Mention promo code MFRPAKZ5. Item #6188.

Inspiration for edible alchemy.