The process for making yogurt is very similar to the process for making buttermilk, but it uses a thermophilic culture, which needs heat to work. The milk must be at 110°F to 120°F in order to culture.
There are a number of different yogurt cultures available, including streptococcus thermophilus, lactobacillus delbrueckii subsp. bulgaricus, lactobacillus acidophilus. Different cultures can create thicker, tangier, or sweeter yogurt, and you can experiment to find one that you especially like.
Directions usually come with the yogurt cultures along with recommended times for culturing, but you can decide how long to culture it based on your preferences. As it cultures, the yogurt will become thicker and tangier.
A commercial yogurt maker will keep the milk at the correct temperature while it cultures. But you can also put it into a thermos or set the jar of milk with added culture in an insulated cooler that is filled with 120°F water or that has a heating pad in it that will heat the milk to a temperature in the range of 110°F—120°F. Be sure to check the temperature of your heating pad first by putting a jar of water in the cooler to see whether the low, medium, or high setting gets the water to the correct temperature range. (You should also check the temperature of water in your cooler before trying it with yogurt. Some coolers are more insulated than other.)
Fruit-flavored yogurt is easily made by adding a tablespoon of your own homemade jam to a bowl of yogurt before serving. I also love adding maple syrup or granola to homemade yogurt.
You can reculture yogurt, essentially using it as a mother culture, provided the yogurt is not more than a few days old. After a few days, yogurt starts to loose its oomph and won’t make yogurt that is thick and creamy. To reculture, we empty out the yogurt jar without scraping or rinsing and refill it with pasteurized milk.
We pasteurize our milk by heating it to 170°F. We let the milk cool to 120°F before adding it to the “dirty” yogurt jar. We stir it up and then pour it into a clean jar to culture. We don’t continue using the same jar because mold will start to grow around the rim after a couple of weeks.
We made yogurt with raw milk for a year or two, but we found it impossible to get consistently good results when reculturing yogurt with raw milk, which is why we started pasteurizing milk to make yogurt.
Others have found that raw milk makes a thicker yogurt than pasteurized, so you will have to see which one you prefer with your milk. Because the natural bacteria in the environment varies from farm to farm, the yogurt made with raw milk will be unique to your farm. And this makes local food unique and interesting.
This is an excerpt from Raising Goats Naturally by Deborah Niemann.