Here's my yogurt recipe. It is by no means perfect, but its a good jumping off point. I've made yogurt 3x and each time I make it I tweak something. From what I've read, it takes some practice to get your yogurt to where you want it in terms of consistency and taste. I've gathered my recipe from various sources. One of the best is here (crockpot version). There are lots of other recipes that call for boiling the milk on the stove to some exact temperature, etc, etc. Here's one here. I found the crockpot way really easy for me and only one pot to clean! So here's what I do:
Homemade Vanilla Yogurt
1. Pour 8 cups of milk into crockpot and mix in 1/2 cup of sugar and 1+ tablespoons of vanilla. (I've used whole and skim and I don't see a difference in consistency so I'm sticking with skim.) Cook on low for two and a half hours. (Can add 1-2 packets of unflavored gelatin or dry milk to help thicken yogurt.)
2. Turn crockpot off and let the yogurt cool for 3 hours. (I think this is where I have problems. You have to cool the milk to 105-110 F before adding the starter yogurt. I'm not sure I'm getting it cool enough. I may try the next batch with a thermometer.) Let me stress that this is an essential step. I accidently skipped it once and ended up with sour smelling milk the next morning, not yogurt. :-)
3. Remove 2 cups of warm milk from the crockpot and whisk 1/2 cup of starter yogurt in. (I use Dannon All Natural.) Dump mixture into the crockpot and stir.
4. Cover crockpot and wrap with a large beach towel and let it sit for 8-12 hours. You will have yogurt after that!
5. If the yogurt is too runny for you, here's what I did. I lined a colander with coffee filters and placed it over a large bowl and dumped the yogurt into the colander. I let it sit in the fridge for about 12 hours and came back to thick yogurt. (I'm told its like Greek yogurt consistency.) I'm going to cut the draining time next time because it was a little too thick. By the way, the stuff you drain out is called whey and I guess its good for you. Some people add it to smoothies, etc.
You can also add fruit to your yogurt to make different flavors. Just be aware that it will make the yogurt thinner.
A 32 oz container of yogurt is $2.99. A half gallon of milk will cost you about $1.50. You will use 1/8 of the yogurt so about 40 cents worth. Your cost to make about 60 oz of yogurt is less than $2. Less if you get the yogurt and milk on sale. So its definitely a money saver if your family likes yogurt.
Edit: Right after I wrote this I went to strain the rest of my yogurt, but it was already thick! I had added two packets of unflavored gelatin with the milk in step 1 and it must have thickened more as it cooled in the fridge. I had excluded this because previously I had used 1 packet of gelatin and it hadn't worked, but I guess 2 packets did the trick! I plan on trying to thicken my next batches of yogurt with dry milk because I think this will be cheaper than gelatin in the long run.