Cultured Dairy (Yogurt, Kefir, etc.)

by Catherine Haug, August 19, 2011; updated January 14, 2012 (Seed & Nut Milk section)

At this month’s Gathering on Lacto-Fermentation, Jeanette Cheney demonstrated how to make several fermented beverages traditionally made from milk (but her samples were made from coconut and soy milk). One of the questions from the audience concerned why and when do you need to sterilize the milk (heat to 180° F) before adding the culture.

I’ll admit that when I first starting making yogurt, kefir and other cultured dairy products, I too was rather confused by this. But after much experience, I think I have a good understanding to share with you.

What is different about these cultures?

Yogurt is thick and creamy, like a pudding. However, homemade yogurt is usually a bit thinner than commercial yogurt. This is because the commercial products add powdered milk or other ingredients to produce a thicker product. You can add powdered milk or agar-agar (a gel thickener for seaweed) to thicken your yogurt, but I make mine without these. See The EssentiaList: Culturing Milk for my photo essay on making yogurt from raw milk.

Kefir is thinner than milk, and slightly effervescent. It is usually consumed as a beverage.

Piima, Villi and Fil Mjolk are Scandinavian cultures similar to yogurt. See Yogurt that cultures at room temperature

The primary product of all these cultures is lactic acid, a beneficial fatty acid involved in many metabolic processes. But other short-chain fatty acids such as acetic acid, butyric acid and glucuronic acid, and also alcohol may be produced by the culture.

The microbes

Yogurt must contain two types of bacteria to be called ‘yogurt’:

L. bulgaricus and
S. thermophilus.

The latter requires a warmer culturing temperature than room temp, ideally 105° – 115° F; together they provide the familiar sweet-tart flavor and creamy texture of plain yogurt. Many commercial yogurts also add L. Acidophilus and other Lactobaccillus and Bifidus cultures to provide specific health benefits. However, for the most part, yogurt’s bacteria are only transient in the human gut, and will not colonize there.

Yogurt is reculturable, meaning that a portion (1 tsp per quart of milk) of a previous batch (or commercial yogurt) can be used to culture the next batch. However, it should be plain, unsweetened yogurt that you use as a starter.

And it is a fussy culture, needing warmer than room temperature to grow, doesn’t like to be crowded, and it has difficulty out-competing foreign bacteria for milk sugar. Therefore:

Pasteurized milk MUST be preheated to 180° F to sterilize, then cooled to culturing temp (about 110° F) before adding the culture.
Raw milk must also be preheated because it is teaming with microbes that do not get along well with yogurt’s bacteria. You may be able to heat it only to 120° F, to preserve much of the natural enzymes. In my experience, however, I have to heat to 180° to keep the milk from separating before it can culture; this also produces a thicker, more pudding-like end product.
After inoculating, allow it to culture in a warm spot, ideally 105° F. When it has started to thicken, and has the desired degree of sourness, transfer it to the fridge where it will continue to thicken.

See Mother Linda: To Heat or Not to Heat (1) for lots more on this topic.

Kefir contains a mixture of bacteria and yeasts. Powdered kefir culture has fewer types of microbes than kefir ‘grains’. Kefir contains various beneficial bacteria and yeasts that are believed to colonize in the human gut, to help restore bacteria lost from overuse of antibiotics or disease. I use Body Ecology brand starter which is ‘reculturable’ (a portion of a previous batch can be used to culture a new batch), and contains the following microbes:

Lactococcus lactis subsp. lactis
Lactococcus lactis subsp. cremoris
Lactococcus lactis subsp. diacetylactis,
Leuconostoc mesenteroides subsp. cremoris
Lactobacillus kefyr (thermophilic)
Klyveromyces marxianus var. marxianus
Saccaromyces unisporus

Yogourmet kefir culture (2) is not considered to be reculturable.

Kefir grains are not granular, but rather have an appearance similar to cottage cheese, but more firm and tend to clump together. Traditional kefir is always made from the grains, and reportedly provides more health benefits than kefir made from powdered culture. The grains contain many more types of microbes than the powdered culture, including L. kefiranofaciens which is responsible for the formation of the soluble polysaccharide, Kefira, and may be responsible for propagation of the grains. See Dom’s Kefir In-Site (3) and The EssentiaList: Using Kefir Grains for more.

Kefir is not as fussy a culture as yogurt, and it’s microbes are quite strong against competitors. Therefore:

You do not need to sterilize the milk before culturing, whether pasteurized or raw.
Simply warm to culturing temperature (90-95° F), and let culture at room temperature.
Because raw milk’s microbes remain part of the mix, with time, they affect the microbe content of kefir grains, but this is not necessarily a bad thing.

About Dairy Milk

For these cultures you can use fresh milk from a cow, goat, sheep, donkey, buffalo, water buffalo, camel, yak, mare, and so on. Of these, I’ve only used cow and goat milk.

You can use fresh (raw) milk or plain pasteurized. I do not recommend using ultra-pasteurized or UHT (ultra-high-temperature pasteurized milk sold in aseptic containers, that does not have to be refrigerated). These may not culture properly. I use fresh milk.

For yogurt, both pasteurized and fresh (raw) dairy milk must be sterilized to get the best results. For kefir, neither require sterilization.

Cows milk is most readily available, and produces a cultured product similar in texture to those commercially available.

Fresh cows milk, and our local Kalispell Kreamery pasteurized milk has the cream at the top, so has to be shaken each time it is used. This separation continues after culturing, and I love to skim off the cultured cream to use in recipes calling for sour cream or creme fraiche. I also love to add a dollop to a bowl of fresh berries or peaches.

Goats milk doesn’t separate into milk and cream fractions, so you will not get a layer of cultured cream at the top of your yogurt or kefir. Goats milk produces thinner cultured products than cows milk, and it has more surface tension (a weird tendency to return to the original container from your spoon). Some goat milk will take on a ‘goaty’ flavor after a couple days, something I don’t mind but some are put-off by this.

Seed and Nut Milk

Jeanette Cheney of WEC (Wellness Education Center in Kalispell (4)) has a lot of experience making cultured products from seed and nut milk, and demonstrated two of these at our recent gathering on lacto-fermentation.

Until recently, the only experience I’ve had with alternative milk cultures is commercial coconut water kefir, which is delicious and effervescent. It is made not from the pulp of the coconut, but rather the ‘water’ that pours out the holes of the whole coconut.

However, as of the January 14, 2012 update, I have now made yogurt from homemade almond milk and commercial coconut milk.

Almond milk yogurt: I made my own almond milk. Almonds don’t have enough sugar to feed the microbes, so I added dehydrated sugar cane juice (honey, sugar, maple syrup or lactose crystals can also be used).

It didn’t do well with yogurt culture (I did sterilize it by heating to 180° F and then cooling to culturing temperature of 110° F).

Next I tried using Body Ecology’s Vegetable Culture (6) powder (as recommended by Renegade Health (5). For this, no sterilization is required, and it is cultured at room temperature. I used 1 quart almond milk and one packet of culture. After the recommended 8 hours, it had separated into a creamy fraction and a watery fraction, which is normal for almond milk. After draining, I got less than 1 cup of a yogurt-like pudding. It tastes good, but I was disappointed in not getting more for my labors.

[Note: Body Ecology’s Vegetable Culture (6) contains the following microbes: L plantarum, L. lactis (3 subspecies) & Leuconostoc mesenteroides ssp. cremoris.]

Coconut milk: I had much better luck with this. It has enough sugar for the microbes, so you don’t need to add any sugar. And it did culture with regular yogurt culture.

I heated it to 180 F as recommended by Angela’s Kitchen (7), and then cooled to culturing temperature of 110° F before adding the yogurt culture powder (1 Tbsp of Natren brand). It cultured for 8 hours at about 110° F. At that point it had started to thicken and had a sweet-sour tang. I transferred it to the fridge where it continued to thicken. It has a nice coconut flavor with a slightly sour tang, and has a yogurt-like texture.

Nut milk kefir: I have yet to try this.

For more information

Mother Linda on Yogurt: To Heat or Not to Heat
Yogourmet kefir culture
Dom’s Kefir In-Site: users.sa.chariot.net.au/~dna/kefirpage.html (NOTE: Dom’s site had been hacked and contained malware, but that has been corrected and the site is now safe).
Wellness Education Center
Renegade Health: Almond Milk Yogurt
Body Ecology: Vegetable Culture Starter
Angela’s Kitchen: Coconut Yogurt

The EssentiaList