This summer, I have been trying to concoct my own yogurt without a lot of success. Apparently, the process is tricky and takes some practice. My first batch was laughable, and resembled only slightly thick milk. After some online digging, I found out I was heating my milk too hot and then killing my starter. The next batch, which I only heated to 120 degrees F (instead of 180F like I previously was told), had all the yogurt on the bottom and a thin layer of whey and milk on top. But at least I was seeing progress.
Third times the charm in this case. After two botched batches I finally got it right, even if it is a bit runnier than store bought. Now I feel confident posting it here.
Plain Homemade YogurtWash out two 500 ml glass canning jars. Set aside. Place a full kettle of water on the boil. Doesn't need to be boiling, but near boiling.
You will need:
1 liter (4 cups) of milk
1/4 to 1/2 cup of plain yogurt
Yogurt makes more yogurt, who knew? Make sure you buy yogurt with *live bacterial cultures*. Any milk will do, from skim milk to whole milk or even raw milk.

In a saucepan warm up milk to 120 degrees F. Use a cooking thermometer and keep any eye on the temperature. Remove from heat and let cool slightly. Take about 1/2 cup of warm milk from pan and mix with your yogurt starter. Then add it back to the sauce pan.
Pour the milk/yogurt into the two jars. Place on the lids and put them both into a insulated cooler.

Take your kettle of near-boiling water and pour the water into the cooler, all around the jars. Close lid. This will need to stay for about 8 to 10 hours. You can do more. I was pushing 12 hours incubating before I found success. When time is up place both jars in the fridge. The mixture will thicken as it cools so you won't know if it worked until a few hours later.
Depending how my next few batches go, I may cave and buy a yogurt maker. Yogurt makers regulate the incubating temperature and provides more consistent batches. I wanted to try this version with the mason jars and cooler, using materials I had on hand before I dole out money on yet another kitchen appliance.