I love yogurt and eat it every chance I get. My kids really enjoy yogurt too and I like the fact that it has some nutritional value. But it's become too expensive to eat everyday if you buy it from the store. So, in my never ending quest to supply all things good and healthy for my family, I began a search to find a full proof recipe for home made yogurt. I searched for several months off and on with limited success. I finally put a few recipes together and after lot of trial and error found a consistent, easy system for making yogurt. I posted a "how-to" for home made yogurt on the Associated Content website several years ago. This is the updated version.
First you need a yogurt "start": a small amount of yogurt that has the acidophilus bacteria. Most of the store bought yogurt has this bacteria you just have to look at the ingredients on the side of the carton. So I usually purchase the largest container for the lowest price of store brand, plain yogurt with acidophilus. I divide the whole container up into ice cube trays and freeze them when home. After freezing, I can pop them out into a large plastic baggie and store them in the freezer until I want to make yogurt. It just so happens that each ice cube is about one tablespoon. This is your "start" but let it thaw before adding to the recipe if you are going to use a frozen yogurt cube.
Second, place a quart of milk into a sauce pan, mix in 1/3 cup of powdered milk and slowly heat. I usually fill a quart Mason jar of skimmed milk then use the same jar later to store the yogurt in the 'fridge. Be Careful, the slow heating is important because milk scorches pretty easily. You need thermometer that will register low temperatures so a candy or dairy thermometer is perfect. These are easy to find. Just look for one at the super market when you are buying the yogurt.
Third, heat the milk to a temperature of 180˚. Then turn off the heat and allow the milk to cool to 115˚. Once the milk has cooled to 115˚ add the tablespoon of yogurt. Remember, if you have a frozen cube of yogurt, you must let it thaw before using. Pour the milk mixture into your quart jar and screw on the lid. Place the full jar onto a heating pad set on the lowest temperature. I then usually cover the jar with a large pot. Don't disturb the jar. After 8 hours you have yogurt. The consistency is a little thinner than the store bought kind. But I don't care and neither do my kids. The best part is that you can add whatever combinations you want: fruit, vanilla, sugar....
A gallon of skim milk costs about $2.25 at a large box store in my area. Therefore a quart of milk costs about $.56. Wow! A whole quart of yogurt for 56 cents! Pretty good. We can eat yogurt everyday now if we want.