Okay, here's the thing you need to know about yogurt. It's really really easy. I tell you this at the beginning, before you read all about getting a thermometer and temperatures and bacterial process and all, because I was intimidated by yogurt for years. I would read the directions, in numerous books, and then put them down and relegate yogurt making to the someday when I have a lot of time to figure it out category in my head. I don't want you to do the same thing. So I'll say it again, making yogurt is simple.
Now, I'll probably be very long winded about making yogurt because I like to understand WHY things work. "Why mommy? Why?" I'm not that different from my 6 year old after all. "But why mommy? Why shouldn't I pee on my little sister in the bathtub? She's laughing."
Here's the other thing you need to know about yogurt. You will save a lot of money making it yourself. Say one gallon of milk is $3. One quart of good quality yogurt is usually $3-4 minimum. That means if you are buying yogurt you are paying $12-16 per gallon. If you make a gallon of yogurt guess how much it costs? That's right, $3, give or take the price of a gallon of milk. If you like yogurt, you really want to know how to make it yourself.
The first thing you will need is a pot large enough to hold the amount of yogurt you want to make. I don't recommend trying to do more than a gallon at a time. It takes too long to heat and burns on the bottom, and too long to cool. But you can start with less. You will have exactly as much yogurt as milk that you start with so you will need containers to hold them. My personal preference is glass mason jars. They seal nicely, don't leak, don't leech dioxins when they are warmed and look pretty. I went through a lot of plastic containers before I caught on. But you can use whatever you want. Really. It doesn't even need a lid. The picky among us may want a wire sieve, but that's completely optional.
So for you who like it laid out all neat and tidy instead of lost in the narrative, here's your list.
Large Stock Pot or Sauce Pan (Heavy bottomed is best.)
Candy thermometer (Can be found in the baking section of every grocery store chain in North America I think. But I'll tell you what to do if you haven't got one too. Yogurt makers have been going by feel for centuries.)
Whisk or spoon for stirring
(See that jar with a bit of yogurt in the bottom? That's
from my last batch, to use to start this one.)
Milk (Whole, Skim, and every thing in between. Personally I think whole milk tastes better and makes creamier yogurt, but low fat will work just as well.)
1 tbsp of your favorite brand of plain unsweetened yogurt, as long as it reads on the side, "Active bacterial cultures".
And please tell me that your favorite yogurt doesn't have gelatin or cornstarch in it, because those people who make that slop don't know how to make yogurt. Well, they probably do, but they're cheating you into thinking that it's creamier with additives. Anyway, you could go out and buy a yogurt starter like yo-gourmet or the like, but it's a whole lot simpler to just use some yogurt you already have. Their instructions are way to complex in my opinion, though that's how I started.
Yogurt is a simple bacterial process, just like bread. You introduce the bacteria to the milk, get it nice and cozy so that the bacteria thrive and they eat their way through all of the lactose and in turn give you yogurt. Before you get all grossed out by that, consider that you have a lot of bacteria and microorganisms in your body right now and you want the stuff in yogurt in you, because it's good for you, and then the bad bacteria has less space to run around and eventually almost moves out altogether complaining about over crowding. So that's why you need a little bit of yogurt from somewhere else. It already has live bacteria in it for you to add to the milk.
The rest is just all about temperature. You get the milk hot enough to pasteurize it so that the only thing alive in it is the bacteria you want to grow and nothing else. Then you get it cool enough to not kill the bacteria and then keep it warm enough that they stay active until they have spread through out the yogurt. Got that? Good. Here we go.
Pour the milk into the pot. Set the heat beneath the pot to medium/medium high. (There are those who will tell you that you should put it on low and stir constantly to keep from burning but those people don't make yogurt that often I don't think. Higher heat warms it faster before the stuff on the bottom starts to stick and burn.) Put the thermometer in the milk, it should have a clip for the side of the pot, and stay close by stirring from time to time.
The hardest part about making yogurt is keeping the milk from burning. It takes so long to heat up that you have usually forgotten that you have anything on the stove and you have gone off to fold laundry or have a shower or something. If you get at all engrossed in movies, do not try to watch one while making yogurt. You will forget about it until it's boiling over the top and burnt on the bottom. Oh wait, that's just me? Never mind. Magazines are good. Yogurt making is a good time to read a magazine. On a chair or stool in the kitchen. Next to your milk. So you don't forget.
Watch your yogurt, stirring occasionally, until it reaches 180F, or 80C. If you have no thermometer, stand over it and watch until the outside edges are bubbling vigorously and there is a lot of steam coming off the milk.
Here's for the list people.
Preheat oven to 110F. Or just set it on the lowest possible setting just when the light comes on, no more. Heat milk to 180F, 80C. Remove immediately from heat. Allow to cool to between 110-115F, about 54C. (Or if you have no thermometer, until you can hold your pinkie finger in the milk for a full 10 seconds without it burning.) Skim the skin off the top. Add the tbsp of yogurt. Stir together. Pour into storage containers. Place storage containers in the warmed oven. Turn the oven off. Wait 4 to 8 hours before opening. When the milk stays firm when the container is tilted remove from oven and place in fridge.
There you're done. That wasn't so hard was it?
Oh the sieve? That's for people who want a very smooth yogurt. You can pour the milk through it into the storage containers to catch any lumps.
I don't usually bother sterilizing my equipment. But I do try to get it very clean, rinsing in very hot water and soap just before I use it all. I don't want anything that isn't healthy bacteria growing in my milk.
Be sure to save a little bit of this batch of yogurt to use for starting your next batch.
For breakfast pair it with Muesli.
Alternate Methods of Incubation
How to "Rescue" Yogurt that Doesn't Turn Out
Greek Style Yogurt, and Making Yogurt Cheese