Smallish amount of yogurt:
4 cups of milk (whole milk works best, but low fat is just fine)
1/2 cup of powdered milk
1/2 cup of plain yogurt that has active cultures (this is where you get your live cultures)
Some way to insulate your yogurt for 12 hours. I use my crock pot because it is so insulated, and wrap it in a quilt - unplugged, of course.
First, many people will pasteurize the milk before making the yogurt. I don't, but if you prefer, you will want to bring your milk up to 185 degrees F, then let it cool down to 120. Otherwise, pour your milk and powdered milk in a pan on the stove and slowly (stirring constantly) bring your milk up to 120 degrees F. You do not want your stove on high, or it will scald your milk and make it taste nasty. Do this slowly, while stirring, with your stove on medium. Once you hit 120F, turn the stove off and stir for another minute or so. Grab your yogurt that you are using for culture and pour it in a bowl - then pour about a cup of your warmed milk in the bowl and stir them together until your yogurt is nice and runny. This will keep it from clumping when you pour it in your milk mixture. At this point, you want to pour the yogurt in your milk mixture, stir well, (if you want vanilla yogurt, or sweet yogurt, now is the time to stir in vanilla - and/or a quarter of a cup of sugar. I prefer not to sweeten it.) and insulate your entire mix. There are different ways to insulate it, including a commercial yogurt maker, a crock pot, etc. I pour it in my warmed crock pot (not hot, just not cold), put the lid on, and wrap the whole thing in a quilt. --- let sit undisturbed for 12 hours or so. If you don't like tart yogurt, let it sit for 8 hours, if you like it really tart, let it sit more than 12 hours.
After the time is up, stir your yogurt and put it in your fridge --- it's ready! When you want to eat it, you can add a sweetener and/or some fruit compote. Sometimes we just add some jelly to it.
The gallon recipe:
1 gallon milk (whole works best, but low fat is just fine)
1 cup of powdered milk
1 cup of yogurt
Follow directions as above! Again, I use my crock pot to insulate it (keeping it in the base, even). -- wrap it up really well with blankets, towels, whatever works.
Greek Yogurt and Yogurt Cheese:
Once your yogurt is done, grab a strainer, a coffee filter, and a bowl. Put the coffee filter in the strainer, and keep the strainer over the bowl. Pour as much of your yogurt as will fit in the strainer/coffee filter, and place in the fridge (keeping it over the bowl of course). This will strain some of the whey off so that your yogurt is thick. In a few hours, it should be thick enough, but if not, leave it longer.
If you are making yogurt cheese, do as above but leave it there for 12 hours or more. I've left it straining for more than 24 hours.
Throw that whey in your smoothie or something, so it's not wasted! It's very healthy.
*It sounds harder than it is, but I can assure you that the second time around, it's super easy. Once you get the hang of it, you don't even measure.... just eyeball it and it only takes a few minutes once your milk is heated.