Homemade Yogurt

This recipe was kindly given to us by Bob and Carol Ahlers on TIME ENOUGH.  It makes a delicious, pourable yogurt that's wonderful on all sorts of things.  And it's really good for you!  It's unlike most yogurt you buy in a typical grocery store; that stuff usually has weird things like xanthan gum or agar in it to make it thick.  If you like your yogurt gelatinous instead of milkshake consistency, you can add a little bit of unflavored gelatin once your yogurt's all set up.  But we like it just the way it is.

First, come up with some way that you can incubate your yogurt at a consistently lukewarm temperature.  
We use a liter-sized insulated thermos bottle and place it in a not-too-hot, not-too-cold corner of the galley.  If you don't have a thermos, you could wrap towels and blankets around your pot to keep it warm, stash it in one of those hot/cold bags, or maybe keep it in a closed oven that has a pilot light.  You'll have to experiment, or just go buy a thermos.  If you eat a lot of yogurt, your thermos will pay for itself quickly.  

Make sure your containers and any utensils you use are absolutely squeaky clean before you start.

3 cups water mixed with 1.5 cups of good quality powdered milk
3 cups of milk

2 tbs of plain, fresh, unsweetened yogurt

Stirring constantly, heat your milk slowly until it almost simmers - look for small foamy bubbles around the edge of the pot.   When you see the bubbles, remove your pot from the burner and let it cool to wrist temperature (about 105-112 degrees). Stir the 2 tbs of yogurt into the cooled milk, and then incubate your mixture for 6 to 8 hours.  

So how can you start off with two tablespoons of yogurt and end up with 3 cups?  What's happening during the incubation period is a little like what happens when bread dough rises.  Your starter culture of yogurt (the two tablespoons) contains lots of different bacteria (the beneficial kind), and when you give the little beasties all that yummy milk to roam through, they feast on the sugar that's present (called lactose) and rapidly multiply.  It's important to make sure that the milk has cooled down enough before adding your starter culture, since high temperatures will only kill them.  If the milk's too cool, the bacteria will still grow, but at a slower rate.  

If your first attempt doesn't quite work, review the essentials again:  spotless containers and utensils, a good starter culture of yogurt, and a consistently nice temperature that's not too hot.   It may take a couple of tries to get everything right.  Once you've got the hang of it, and you always make sure to have at least 2 tbs on hand, theoretically you never need to buy yogurt again, just milk!