I got into Yoghurt making a long time ago. I was on this whole "gotta cut down on sugar" kick. It would have been a lot healthier if I had quit shooting dope, but hey, first things first you know? Anyway, I am acting like a sugar cop in the store and I get a carton of plain yoghurt. When I read the label I notice that it had high fructose corn syrup in it. I'm trying to cut down on sugar and these bastards are plotting to pour karo syrup down my throat. I figure enough's enough so I start doing a little research about it.
The first thing you need is a half gallon of milk. Some people prefer skim milk, and that's fine with me. I use skim milk from time to time, but most of the time I just use what ever is in the fridge. Put this on the stove over a high medium heat. To the milk add a can of evaporated milk and 2 cups of nonfat dry milk. This increases the milk solids that are present and will improve the consistency of your end product. Heat until a covering of small bubbles is present and it is almost boiling. If it does boil it's no big deal, it just makes a horrid mess is all. The main thing you want is for the temperature to reach at least 180° for a minimum of two minutes. This kills any other bacteria that might be present and readies the milk for the introduction of the bacteria we want. Let the milk cool down to a little above body temperature (warm, not hot) and add the yoghurt starter. There might be a skin formed on top of the milk. In Poland this is called a ploika and is eaten on hunks of bread. Mine go to the dogs, if they don't get their issue they might not let me move away from the stove. For a half gallon batch, half of a small carton of plain yoghurt (and don't forget to read the label in case the syrup spies have been active in your neighborhood). The best way is to scoop some of the boiled milk over the yoghurt culture in a 2 cup measure and mix it until smooth. Stir it into the rest of the boiled milk and then transfer to a clean, airtight jar. (I like the Kerr small canning jars, single serving size) If you don't have a yoghurt maker (I love my Danvier) you can use a rack style dehydrator, or barring all of that put the stove on warm (you're going for an average temp of not less than 110° yet not more than 120° I found that the "warm" setting on the oven dial with the door slightly cracked worked just fine. If you are using the oven method you will want your jars in a bain marie which is a fancy ass french way of saying put the jars in a 12" by 8" baking pan and the add water around them. This will ensure that the yoghurt sets up evenly in your containers.
Leaving it alone for about eight hours should do the trick, but the longer you leave it in the heat the tighter your yoghurt will be. If you pick up one of your jars and it looks and feels solid in the jar, you're done.
There are some variations. In India they will take the finished yoghurt and strain out much of the liquid through a cheesecloth. It makes a cheesier, denser yoghurt. There are a lot of things to do with it from here. I substitute it for around half of the mayonaisse when making tuna or potato salads. There are lots of Turkish, Lebanese and Indian dishes that use yoghurt.
Since this isn't pasturized again there will be live culture stuff present and you'll want to make new yoghurt after two weeks in the refridgerator. Give this one a try and you'll end up hating the stuff they pawn off on you at the store as much as I do.