Culturing Milk: Yogurt

Freshly cultured yogurt

by Catherine Haug, June 28, 2011

(all photos by C. Haug)

Don’t you just love that sweet-tart flavor of creamy white yogurt? Or do you prefer yours with honey and fruit stirred in? Did you know that yogurt is a lacto-fermented food that you can make at home?

Yogurt is a very popular food, as major brands like Dannon have promoted yogurt’s ability to normalize a troubled digestive system. It’s the probiotic bugs in yogurt that do this good work, but you don’t need to buy these advertised brands to get the same benefit.

Our August gathering will be on lacto-fermentation, which includes the culturing of milk to make things like yogurt, cheese, sour cream, butter, and kefir. (See also my recent post: Lacto-Fermentation or Live Culture, and The EssentiaList: Yogurt & Kefir, from Powdered Culture).

Read on for a photo essay on how you can do this at home. See also printable pdf version of the photo-essay: Making Yogurt at Home: a Photo Essay.

The Process

(See below for detail of Ingredients & Equipment.)

NOTE: This photo-essay is for making true yogurt, which is a thermophyllic culture (cultures at above room temperature, ideally 100° – 116° F). Mesophyllic yogurt-like cultures are also available that culture at room temperature, but the method is a bit different.

Before starting, you will want to find a warm space for your yogurt to culture,  between 95° and 116° F. See below under ‘Equipment for more detail.

Step 1: Assemble ingredients (clockwise from upper left):

  • milk
  • plain, unsweetened yogurt as inoculant (a previous batch)
  • powdered yogurt inoculant (optional)

Ingredients for making yogurt

I made 2 quarts yogurt for this demonstration, so used:

  • 2 quarts (8 cups) milk
  • 2 tsp plain unsweetened yogurt (don’t overdo – this is one time when more is not better. Yogurt doesn’t like a crowd.)
  • few sprinkles powdered yogurt inoculant, optional (one envelope pictured above will make 1 quart of yogurt if already cultured yogurt is not used, or will make at least 6 batches if used with already cultured yogurt. See below for more on this)

Step 2: Pour milk into saucepan, insert dairy thermometer, and heat to 180° F.

Heat milk to 180 F

Milk heated to 180 F

Step 3: Then set saucepan into a water bath to speed up the cooling of the milk to culturing temperature (100° – 116 F). This takes 15 – 20 minutes.

Warmed milk in cooling bath

milk cooled to 115 F

Step 4: Remove saucepan from cooling bath.

Step 5: Prepare inoculant:

  • If using only powdered inoculant, pour about 1/2 cup warm milk into small bowl. Dump the powder from the packet onto the milk and stir well until it is all dissolved
  • If using plain unsweetened yogurt (method shown here), measure 1 tsp per quart (I use 2 tsp) into small bowl or measuring cup. Add about 1/2 cup warm milk and stir until all is well mixed.

Add yogurt inoculant to small bowl

NOTE: As shown below, I usually add a few sprinkles of powdered inoculant to my yogurt inoculant because I like the flavor, and to keep my yogurt strong (see below for more.). Stir this into the yogurt to mix.

Add powdered inoculant, if desired

Add warm milk to inoculant

Stir to mix warm milk and inoculant

Step 6: After inoculant is thoroughly blended with the 1/2 cup milk, pour mixture into saucepan of milk and stir. I usually pour some of this back into the small bowl, stir, and add back to the saucepan twice more to ensure it is thoroughly mixed. 

Stir dissolved inoculant into warm milk

Step 7: When well mixed, pour into jar(s). Add lids, and set in warm spot to culture.

Inoculated milk in jars, ready to culture

Step 8: I set my lidded jars in a warm water bath to help stabilize the temperature in my warm spot: my gas-fired oven, warmed by a pilot light, then close the oven door. The water bath is especially important if your warm spot is subject to breezes that could cool the mixture.

Inoculated milk in warm spot (my oven warmed by pilot light)

Your yogurt should be ready in 4 – 6 hours. After 4 hours, take off the lid and insert a knife; the yogurt should divide at the insertion. Remove knife and taste. If it is tangy (tart), it is done. If not, replace lid and allow to culture a bit longer. The batch I made for this photo-essay was ready in 6 hours).

Step 9: When ready, store covered jars in fridge or other cold spot (such as a cold root cellar). Will keep a long time, undisturbed and with the lid on, in cold storage. The lid will likely form a weak seal as the jar cools, which helps with keeping time.

Freshly cultured yogurt, ready to eat, is shown below. It has a nice ivory color because I use whole milk. I like it just like it is, naturally sweet-tart. But you can stir in honey and/or fruit when you serve it, if desired.

Freshly cultured yogurt

If you need help with troubleshooting, you can email me (Cat), or check out the Mother Linda on Yogurt website (5).

Ingredients & Equipment

Milk: Raw or Pasteurized

You can use commercial milk that has been pasteurized (vat process or HTST process such as Kalispell Kreamery), but I would not recommend using ultra-pasteurized milk, because the casein is damaged and may produce a gritty product. See Food Safety and Pasteurization for more on pasteurization.

I start with raw milk, but after many frustrating failures using it raw, I admitted that I would have to pasteurize it (heat to 180° F) first. This is because the bacteria that thrive naturally in the raw milk, out-compete the yogurt culture and cause the casein to coagulate and separate, thus keeping the yogurt culture from being able to work.

After pre-heating the milk, it must be cooled to culturing temperature (110 – 116° F) before adding the culture, to avoid killing the yogurt culture.

I am not a fan of pasteurized milk, but making yogurt out of pasteurized milk restores much of the enzymes and vitamins destroyed by the pasteurization, so this is a compromise I am willing to make for the health-promoting ability of yogurt and it’s wonderfully sweet-tart taste. See The World’s Healthiest Foods: Yogurt for more on the health benefits of yogurt. (1)

If you don’t want to pasteurize your raw milk, try a slightly different, mesophyllic culture, such as Viili (Fil Mjolk) or Piima, which work at room temperature and don’t require heat-treated milk. See Alternative Yogurt Cultures below.

Goat vs Cow Milk

I have used both, but prefer cow’s milk for yogurt because it produces a more pudding-like consistency. Sometimes, however, it doesn’t get that thick and has a texture more like kefir.

Goat milk yogurt has a very odd texture. If you put a spoon in it, then remove the spoon, such as to put what you scooped into a bowl, the yogurt will try to get back into the jar because it has such a strong surface tension.

You can add powdered milk to the cow’s milk before heating, for a thicker texture, or to goat’s milk to minimize the surface tension as well as thicken the yogurt. But powdered milk is treated with heat and pressure to evaporate the liquid, and so is less healthful.

True Yogurt Culture

While many brands also add other beneficial probiotics, such as L. casei, and L. bifidus, true yogurt must contain at least these two bugs:

  • L. bulgaricus, a common probiotic bacteria, in the same family as acidpophilus.
  • S. thermophilus is a thermophyllic bacteria, meaning that it thrives at warmer culturing temperatures (110 – 116° F). It is this bacteria that requires yogurt to be cultured at warmer than room temperature.

To make yogurt at home, you can use:

  • Commercial yogurt as the initial starter (and then use your own yogurt to culture future batches). Use 1 tsp per quart of milk. Be sure to select one that says “contains live bacteria” on the container, and I would not recommend the functional food versions such as Dan-Active, as they have specially-bred bacteria that may not work well at home.
  • Homemade yogurt from a friend (or from your own previous batch of yogurt)
  • Powdered yogurt culture such as that from Yo’gourmet; use one 5-gram packet per quart of milk. For true yogurt, buy the one that is Culture Bulgare; Yo’gourmet also has a casei/acidophilus/bifidus version, but is not as sweet-tangy as the Bulgarian yogurt. You can also get yogurt powder from New England Cheesemaking Co. (

For commercial yogurt, I prefer Nancy’s Plain Yogurt, but Stoneyfield, Brown Cow, and Strauss Farms yogurt are also good brands. And I prefer whole milk yogurt to low fat or non-fat yogurt (See my post Dairy fat: healthful or not? for more).

I have been making yogurt from my own yogurt now for about 10 years. But I add a few sprinkles of Yo’gourmet powder to the mix, because I like the flavor, and to keep it strong from batch to batch.

[If you use your last batch of yogurt to inoculate the new batch, with time, it can get weak as it is contaminated with bacteria from the air. By adding a bit of powdered inoculant each time, you minimize this effect.]


  • Thermometer: I strongly recommend a dairy thermometer to track the temperature of your milk during heating, cooling and culturing.
  • 2 – 3 quart saucepan (stainless steel or enameled steel). Do not use aluminum. Saucepan should have a heavy bottom, such as all-clad aluminum or copper. If you don’t have one of these, use a double boiler to keep the milk from scorching on the bottom of the pan.
  • Small bowl or measuring cup for diluting inoculant
  • Stainless steel spoon for mixing inoculant with milk
  • Large pot or bucket for cooling bath (large enough to accommodate your saucepan
  • Glass canning jars (for storage). I don’t recommend reusing plastic yogurt containers, and they can leach toxins into the acidic yogurt.
  • Warm location for culturing.

It’s that last item that is the difficulty for many. Where can you find that warm location in your home?

  • Gas range with pilot light, for oven/broiler.
  • Electric oven with the light turned on.
  • Ovens wtih a setting for proofing bread.
  • A styro-box or other cooler with a light inside works great.
  • Yogotherm insulated container (like a large thermos); I don’t think they hold the heat well enough.
  • An electric yogurt-maker (not my first choice)

See Making Yogurt Without a Yogurt Maker for more ideas.

To test a location, fill a jar with water heated to 115° F. Insert the thermometer and set it in your warm spot. Check it after 4 hours and again at 6 hours. If it has maintained a temperature between 95° and 115° F, it will work.

Alternative Yogurt Cultures

If you don’t want to heat-treat your milk (pasteurize), or if you don’t want to deal with maintaining a warm culturing spot for making true yogurt, you do have options. However, the method is a bit different than that detailed above.

Piima and Viili (Fil Mjolk), from Scandinavia are mesophyllic cultures, which can be cultured at room temperature. The resultant product is similar to yogurt, but not the same.

  • Piima has a runny texture and almost cheesy flavor;
  • Viili (Fil Mjolk) is mildly sweet and gelatinous.

See Cultures for Health: Yogurt Starters or Nourished Kitchen: Homemade Yogurt (mesophyllic vs thermophyllic) for more on these alternative cultures.

Sources and References

  1. The World’s Healthiest Foods: Yogurt (
  2. Making Yogurt Without a Yogurt Maker (
  3. Cultures for Health: Yogurt Starters (
  4. Nourished Kitchen: Homemade Yogurt (mesophyllic vs thermophyllic) (
  5. Mother Linda on Yogurt (

Related ESP Articles

  1. Making Yogurt at Home: a Photo Essay
  2. Lacto-Fermentation or Live Culture (
  3. The EssentiaList: Yogurt & Kefir, from Powdered Culture (pdf:
  4. Food Safety and Pasteurization (pdf:
  5. Dairy fat: healthful-or-not? (

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