To Heat or Not To Heat: A Yogurt Question

In the Kitchen with Mother Linda

One of the most frequent questions we receive at the Foundation is the following: should you, or can you, make yogurt from raw milk? The controversy arises from the fact that the naturally occurring enzymes and bacteria in raw milk are destroyed by too much heat. Destruction of enzymes begins at 118°F and is complete at 180°F. So, if that’s true, why doesn’t everybody want to make yogurt with raw milk? It’s because raw milk yogurts oftentimes have a different texture from yogurts made with heated or pasteurized milk.

Left to its own devices, fresh milk sours naturally. This is not due to the enzymes in the mix, but to naturally-occurring lacto-fermenting bacteria found in raw milk. Those bacteria produce lactic acid that sours the milk by reducing its pH., i.e., making it more acid. While the uninitiated might think this is milk to be thrown out, the wise know this acid condition actually preserves the milk against spoilage. In days gone by, the Irish housewife typically soured fresh milk overnight by the dying fireplace in preparation for making soda bread the next morning.


Frank Kosikowski, a food scientist at Cornell University, classifies fermented milk in four different groups. The first group is “acid/alcohol” milk products such as kefir and koumiss. Kefir (which, by the way, does not rhyme with “reefer” but is stressed on the second syllable and pronounced “keh-FEER”) is made with kefir grains, called “gift of the gods” but of unknown origin, which initiate a dual lactic acid/alcohol fermentation process. Traditional koumiss is made with mare’s milk and named for the horse-herding Kumanes tribe that lived on the central Asian steppes until 1235. It is fermented by a combination of acid producing L. bulgaricus and the alcohol-producing Torula yeast. (With mare’s milk in short supply most koumiss today is made with cow’s milk, but since the two milks are not the same composition, making koumiss can be a complicated endeavor.)

Kosikowski identifies the second class of fermented milk as “high acid” Bulgarian sour milk cultured exclusively with Lactobacilllus bulgaricus. The third category is “medium acid” acidophilus milk and yogurt, the main type of yogurt produced in the United States. It is primarily cultured with Lactobacillus acidophilus, a slow- and low-acid producer. The fourth category is “low acid” cultured buttermilk and cultured cream.

Today, most yogurt starters, even the “Bulgarian” one I recommend, combine at least two different bacteria. The presence of two bacterial strains, one high acid and one low, moderates the acidity of the finished product. For example, Streptococcus thermophilus ferments at 110°F to 112°F and produces .9-1.1 percent acid, Lactobacillus acidophilus ferments at 100° to 112°F and produces 1.2-2 percent acid, and Lactobacillus bulgaricus grows at 110° to 116°F and produces 2-4 percent acid. My favorite yogurt starter is 50:50 L. bulgaricus/S. thermophilus.


Now let’s get back to the “to heat or not to heat” raw milk controversy. What happens when you don’t heat the milk is that while the enzymes are preserved, the milk also retains its own natural complement of bacteria that will naturally sour the milk. These undisturbed bacteria will also compete with any added culture resulting in a different fermented product. Controlling the conditions of fermentation, most importantly temperature, the yogurt maker can achieve varied results by adding small amounts of microorganisms from tested and tried established cultures.

Most yogurt makers heat milk sufficiently to create a tabula rasa into which the new bacteria are dumped to do their handiwork, but the temperature needed for this will be many degrees higher than 110°F. Whatever temperature the milk will be heated to, in my opinion it is best to begin with raw milk. It is not homogenized so you get a wonderful cream on top. It has not had milk solids added to it, so it won’t stick to the bottom of the pan. Most important, raw milk has not been pasteurized, which is a violent, rapid-heating process that has a very detrimental effect on the proteins in the milk. A slow, gentle heating on your stovetop will more effectively preserve the integrity of fragile milk proteins, especially if you remove the milk from the stove as soon as the desired temperature has been reached.

When you start with raw milk, you can decide yourself how high a temperature you want to take the milk to–a modest 110°F, that will preserve enzymes and some of the competing naturally occurring bacteria, or to the more traditional 180°F, which is hot enough to kill competing bacteria. The texture, taste and thickness of the finished yogurt will be determined by the choices you make at every stage.


My own preference is for heated yogurt, which results in a smooth, thick product. I begin with raw milk which I slowly and gently heat to 180°F and then let it cool until I can stick in my finger for 10 seconds, which is around 110°F. When it has cooled, I add a rounded teaspoon of “Bulgarian” culture, which is really only 50 percent true Bulgarian, as explained previously. The finished yogurt comes out sharp, smooth and wonderful.


I want to pass on something I learned while researching the article. I have always made a gallon of yogurt at a time in four quart jars, and kept them up to two months. It does not spoil easily, so my family and I would happily scoop away at it until it was gone–adding our own preserves, maple sugar or honey. My favorite yogurt concoction is a couple scoops of yogurt, sprinkled with a tablespoon of freshly ground flax seed and topped with a quarter or half of a grated apple–applesauce is good, too.

But if master yogurt maker Max Alth is correct, milk begins to exhibit “antibiotic” powers as soon as the lactic acid bacteria start to curdle the milk–either naturally or in the process of making yogurt–and a peak is reached about seven days later. And according to Alth, the antibiotic effect disappears about a week later. At its most effective, the antibiotic strength of yogurt is equal to about .06 penicillin units per cubic centimeter, or about nine units of penicillin in every 8 ounces of yogurt. I have not confirmed this information, but if that’s true, in the future I plan to make smaller batches of yogurt more often.

Anna’s Bulgarian Yogurt

I have had the great fortune of living close enough to a Bulgarian friend, Anna Pavlova, to get a container of yogurt every so often from her as a starter. If you don’t have a Bulgarian friend, a company in California sells a Bulgarian-style Yogurt Starter®. (See and look in their specialty items.) This wonderful product is a combination of 50 percent Streptococcus thermophilus and 50 percent Lactobacillus bulgaricus. Each bottle is decorated with the picture of a Bulgarian woman.

8 cups milk (I prefer whole raw milk)
1/4 cup yogurt from a previous batch
or 4 teaspoons of Natren yogurt starter
as directed on the bottle
2 glass quart jars with lids, sterilized

Over low heat, slowly bring the milk to at least 180°F, or until a ring of bubbles forms around the edge of the pan, but don’t boil. Let cool until you can keep your finger in the milk while you count to 10. Divide yogurt starter or reserved yogurt between two wide-mouth quart-size sterilized glass jars. Pour in about 1/4 cup milk and stir to incorporate the starter. Fill the jars with the rest of the milk and screw on the lids.Wrap the jars in a warm blanket and let sit overnight in a warm place or for at least eight hours. Unwrap and place in the refrigerator. I know you will enjoy this creamy, healthy yogurt.


Max Alth, Making Your Own Cheese & Yogurt, Funk & Wagnalls, New York, 1977
Frank Kosikowski, Cheese and Fermented Milk Foods, 1966.


In the Middle East, yogurt is a thick drink, not something you eat with a spoon. To make raw milk drinkable yogurt, place 1 quart raw milk in a glass container and add 1/4 cup yogurt. Place in a warm place (such as a warm oven) overnight. The milk will sour and become slightly thick and perhaps lumpy.

You can drink this as is, or whisk it to make it smoother. In Iran, the traditional yogurt drink is quite salty, so you may wish to add some unrefined salt. The addition of salt makes drinkable yogurt the perfect beverage for a hot climate. Of course, you may also use your drinkable yogurt to make smoothies by blending with fruit and a natural sweetener.

Another method, suggested by raw-foodist Aajonus Vonderplanitz, is to warm milk to about 80 degrees and add a small amount of good quality commercial yogurt or yogurt from a previous batch and put in a yogurt maker. Leave in the yogurt maker much longer than called for in the instructions, that is about 8 hours or overnight. Results may not be consistent and the product tends to be thinner than heated yogurt.


We are grateful to Maria Garcia for coming up with this wonderful raw milk yogurt, and to Kristina Boudrezux for working out the details. This recipe makes a smooth, thick yogurt loaded with beneficial stuff for your body. It requires no electricity, and ensures a high quality product using glass, versus plastic, for yogurt culture growth. It is easiest to start at night, after dinner, and let it set overnight. You will wake up to yummy yogurt for breakfast.

1 quart raw, organic whole milk
1-8 ounce container Brown Cow whole milk yogurt, plain flavor (for the first batch)
or 3-4 tablespoons reserved yogurt from the previous batch

Keep all of your utensils very clean, making sure there is no soap residue. This is especially true of the “mother” container, described below. Keep the metal lids out of the dishwasher, as this will cause rusting.

  • Nissan Thermal Lunch Tote thermos JLN 1400X), all plastic containers inside removed.
    (Available from 300 N. Martingale Road, Schaumburg, IL USA and in local stores)
  • 1 quart class container with metal, 1-piece lid, sterilized (boiled), then dried and cooled to just warm.
    (The 32-ounce Paragon Jar from California Glass Co. fits the Nissan Thermos)
    (510.635.7700 or
  • The “mother” container, a glass container with air-tight seal,
    4 tablespoon size to hold the starter for the next batch, sterilized
  • Small whisk
  • Measuring spoon for 1 tablespoon
  • Milk or candy thermometer


  1. Take the yogurt starter (Brown Cow, or container from a prior batch–the “mother”) out of the refrigerator for 1 -2 hours, to bring to room temperature.
  2. Warm the 1 qt glass jar, if not already warm. Rinsing in hot water will do.
  3. Heat the milk in a pan to 110°F, then remove from heat immediately.
  4. Take a small amount of the warm milk into a separate bowl, then whisk in 3-4 tablespoons of the yogurt starter. Stir the mixture back into the main bowl of milk.
  5. Pour the milk-yogurt mixture from the pan into the warm, 1 qt glass jar and seal loosely with the lid. Make sure to leave about 3/4 inch of air at the top of the jar so the culture has some space to grow. Place the jar into the thermos and close. Put it on the countertop, and let it set overnight (8 hours).
  6. In the morning, remove the glass jar from the thermos and put it into the refrigerator.
  7. When you first open the yogurt jar, have your smaller container ready for the mother. There will be some delicious cream on the top. Before you do anything else, scoop out 3-4 tablespoons of yogurt (the “mother”), place it in the mother container, and put the mother in the refrigerator for later use to start your next batch–instead of using the Brown Cow.
  8. The yogurt and mother both last about one week. Enjoy your yogurt! Try adding a bit of honey for fun.

This article appeared in Wise Traditions in Food, Farming and the Healing Arts, the quarterly magazine of the Weston A. Price Foundation, Spring 2005.

Linda Forristal, CCP, MTA, is the author of Ode to Sucanat (1993) and Bulgarian Rhapsody (1998). Visit her website at

One Response to To Heat or Not To Heat: A Yogurt Question

  1. sree bhavya says:

    sir i need standards or composition of bulgarian sour milk, can u please send a mail for me regarding to bulgarian sour milk,………..

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© 2015 The Weston A. Price Foundation for Wise Traditions in Food, Farming, and the Healing Arts.