How can anyone live without natural yoghurt?! What do you put with your nachos? (Well, sour cream, obviously, but thick natural yoghurt is even nicer, to my mind.) What do you dollop on your kedgeree? How do you make raita for curries or tzatziki for a Mediterranean meze? How, in short, do you live?
So: make your own! First thing, slight catch. You need some natural yogurt to start with. You don't so much make yogurt as expand yogurt. The bacteria make the yogurt, you just introduce the bacteria to milk in the right sort of romantic conditions. It sounds like you can buy proper yogurt in the States, but it's rare and expensive, so the idea is you can buy one small bottle as your starter and then just keep it going. Yogurt is expensive; milk is cheap. There's a place called Sohha, I believe. Or you might have a local little deli or something. You don't need much - two or three tablespoons. To make sure it's proper yogurt, ask two questions:
1. Does it have live bacteria? (If not, it's not proper yogurt.)
2. Has it had anything added to it, eg sweeteners, syrups, flavours, fruits, etc? (If yes, it's not proper yogurt.)
The yogurt you make will taste the same as the yogurt you buy (because it's the same bacteria) and different strains of yogurt can taste quite different, so make sure you get one you like. My favourite is a good thick Greek yogurt - in the UK, Yeo Valley Greek-style yogurt is my personal favourite brand.
You will need...
2-3 tablespoons of yogurt
That's it. The amount of milk you use is the amount of yogurt you get. I usually make 8 pints (4 litres) at a time, but I eat a fair amount of yogurt. It doesn't matter if the milk is organic or not, raw or pasteurised, normal or UHT, they all work.
(This is a very country-style recipe... approximations galore! It always just works.)
1. Heat the milk. Pour all the milk in a saucepan and heat it gently. If you stir it occasionally, that helps it not stick to the bottom. It's important to heat the milk: it won't yogurt if you don't heat it. Heat it to just below boiling point. (If you have a thermometer and want to be fussy, you're going for 85 C / 185 F, but you really don't need to be precise. And it's fine if it boils. Just don't burn it is all.) It usually takes me about 45 mins to heat that quantity gently all the way up.
2. Cool the milk. Switch it off to cool. It's the right temperature when you can hold your finger in it for 10 seconds. (Again, for people with thermometers and a frenzy with precision, you're aiming for 46 C / 115 F, but again, you do not need to use a thermometer, the finger method works fine every time as well. Although it does involve a certain amount of yelping before the temperature gets down!) This usually takes 30 minutes to an hour, for me, depending on the ambient temperature.
3. Mix in the starter yogurt. 2-3 tablespoons always does plenty for 8 pints of milk, when I make it, but more won't do any harm at all either - it'll just mean your bacteria have a larger population to start with, and will probably procreate a bit faster.
4. Keep the yogurt safe and happy overnight. You want to keep it warm and snug, but not hot. So pour it now into its individual jars, and then find some way to wrap them up all cosily. I use an old wicker hamper, lined with a blanket and a white cloth, and then tuck them in the blanket, and put it somewhere not drafty and quite warm, like the alcove under the stairs near the radiator:
A cardboard box also makes great insulation; so does newspaper. An airing cupboard would do well, if you have one. Sometimes I put the hamper on an armchair, so they're off the floor, if it's a cold wooden floor. Just think of them as sleeping kittens and treat them appropriately.
By the way, yogurt doesn't swell, it just thickens, so you can fill your jars all the way to the top.
5. Pop it in the fridge. After 12 hours or so, they should be thickening nicely. Pop them in the fridge and usually after 3 days they're the right thickness to eat.
Remember to keep a starter yogurt, for the next batch! My smallest jar with the best seal is reserved for the starter yogurt, and goes right to the back of the fridge, to start off a new batch when supplies start running low.