I learned how to make plain homemade yogurt a couple of years ago at a dairy class hosted by our local Lubbers Family Farm. I start with 1 quart of fresh, raw milk and put it in a stainless steel pan on medium heat. I have my thermometer clipped to the side with a chip clip, but when it gets to the higher temperatures, I just hold the thermometer with an oven mitt it the middle while I’m stirring.
I stir pretty frequently as the milk heats up and I watch for the temperature to reach about 180 degrees F (when the milk is really starting to get bubbly). I’ve gone with a little less and not had any issues yet. Once the milk has reached about 180, I remove it from heat and let it cool to about 110 degrees. This can take a while, I normally plan on about 15 minutes of doing something else.
Once the milk is cooled to 110, I add either 1/2 cup yogurt with active cultures (I really like Oikos plain Greek yogurt), but I also sometimes use frozen packets from a local store. The frozen packet brand is New England Cheesemaking Supply Co. I am using a packet today, but if I could always choose the healthiest I’d start with the fresh yogurt (there’s a few extra ingredients in the frozen packets).
Also, once you have made yogurt the first time you can save 1/2 cup to start the next batch (as long as you don’t wait too long to make the next batch) and really not have to buy a starter again. I am not very good at saving this and usually eat all of mine up in smoothies and have to start again from scratch.
Once I stir in either the starter yogurt or packet, I pour it all into a quart jar again and put the lid on tightly. I place it in my small “picnic” cooler and fill it to the neck of the jar with hot water. I close the cooler and let it sit either for overnight or all day if I make it in the morning. When the yogurt is ready I dry the jar off with a towel and put it right in the fridge to get cold (I’m not a huge fan of warm yogurt) ;). And there you have it, that is really all it takes to make homemade plain yogurt!