I regularly make plain yogurt, and it is much cheaper than buying it from the store. You don’t have quite as much control over the final flavor, but I don’t like it sweetened anyway. There is only an occasional batch that is a bit sour tasting.
I make a gallon at a time. I eat one or two 8 ounce tubs a day, and this is a good amount for me to keep around.
Begin with a gallon of milk and 6-8 ounces of existing yogurt. . I use ½% milk, but any fat content will work, it’s your choice. I buy one new tub of vanilla yogurt for each batch, but I have a friend who just uses one tub from the previous batch, and she says she’s never had a batch fail.
You need a pan that will hold the milk, containers to hold the yogurt, a spatula- I like one with a flat edge, and a dipper of some kind. I also like to have an extra small bowl, and a candy thermometer to be sure of the temperatures.
Pour the milk into the pan, and heat it quickly to scalding, which is 180 degrees F (82 C). You will need to stir most of the time to keep it from scorching on the bottom. This is when I like the spatula with a flat bottom because I can keep running it over the bottom of the pan. Turn the heat off when the milk reaches 180 F. It will look sort of foamy on top, but do not let it boil.
Now just let it sit and cool naturally till it reaches 125 F (52 C). If you forget and it gets cooler the yogurt will still set up fine, but I think that some of my more sour batches came from milk that had cooled below 100 F (38 C).
Incorporate the yogurt into the milk. I like to do this by putting the yogurt into a small bowl, then add a little milk and stir until smooth. Then I add a little more milk and stir again, and finally pour it all into the pan of milk.
Then I just dip the milk into small containers. I used washed 8 oz. yogurt cups with lids that I’ve saved. As they wear out I’m replacing them with ziploc containers of the same size, but a flatter shape. It doesn’t have to be small tubs. You can just divide it into four quarts if you want. I always seem to get 18 cups (tubs) even though the gallon of milk and one tub of yogurt should only add up to 17 cups. I’m probably not filling them to their fullest.
The final step is to place the tubs in a warm location for at least 6 hours. I put them in my Excalibur food dehydrator, because it has a thermostatic control. I can set it to 115 F (46 C). But any warm place will do. You can put it near a heater, in an oven with a pilot light, etc. If it will be on the floor near a door you can cover it with a towel to minimize the effect of drafts.
At the end of 6 hours, you can just check that it has set up properly if you want, but it should be done. Put the containers in the refrigerator. I’ve found that they will keep for about a month, and then may start to get moldy. This may be from re-using containers, but I usually eat it up in plenty of time.
With 18 servings, and a total cost of under $4, even when the milk is not on sale, this works out to $.22 per cup. Of course, I do put some fruit on it, but this is way less than grocery store prices.
My favorite way to eat this is with some chopped fresh or dried fruit, and sprinkled with grape nuts or oatmeal.