To give you the layman's background, yogurt is milk that has had a bacteria go through it, converting the lactose (a form of sugar) into lactic acid. In other words, it's fermented milk. The lactic acid then acts on the major protein in the milk ("Casein" - its the bit that holds all the calcium, phosphorus, carbohydrates and amino acids) and causes it to bind into what you know as yogurt.
The bit that always confuses people is if you're making your own yogurt, where do you get the bacteria? The good news is, you just buy some yogurt at the store with "Live" or "Active" cultures (cultures = bacteria), introduce it to some warm milk and leave it for a number of hours to chew through the lactose. Literally, that's it. You can save a bit of your new yogurt to create the next batch, but apparently it runs out of steam after about six re-uses... at which point you'll probably want to buy a different yogurt from the store and try experimenting with that.
You'll see a whole bunch of recipes on the web that call for various paraphernalia and heating pads, towels, thermos flasks, and you don't need any of it.
So, here's the recipe that I did.
- 1 liter of whole milk.
- 3 tablespoons of plain yogurt with "live" cultures.
- First, heat the milk to 185° in a saucepan over a medium heat. Keep stirring as you don't want to burn the milk on the bottom of the pan. This is just to sterilise it of any bad bacteria you might have in it.
- Now, turn off the heat. Let it cool to 110°.
- Add 3 tablespoons of store yogurt. Mix well.
- Pour the milk into a casserole dish with a cover.
- Pop that into an oven with the light on. (In my oven, the lamp alone keeps things at 90-91°).
- Go to bed, leaving it for about 10 hours. Do NOT jiggle, jostle or poke it once in the oven.
When you open up the oven in the morning, you're greeted with what is unmistakably yogurt. It's warm, but it's yogurt. The longer/hotter you leave it, the tangier it becomes, the shorter/cooler you have it, the less tangy.
Now, the next bit is all about preference for the yogurt style; The yogurt your looking at has a watery substance in it. This is whey. You can leave it in for a runny yogurt, or take it out, to thicken things up a bit. I elected to take mine out using this method:
1. Put a sieve over a bowl. Put a paper coffee filter in the sieve.
2. Spoon in the yogurt and leave it for 5 minutes.
3. Spoon it out into a (sanitised) container for refrigerating.
If you want to go greek style, put the strained yogurt in another coffee filter and leave it to strain in your fridge overnight, to remove even more whey.
So to recap:
- Heat the milk to sterilise it.
- Cool the milk to the point where the heat won't kill the active bacteria from the store bought yogurt.
- Leave it in a warm place, undisturbed, to do it's thing.
- Optionally strain out as much or little whey as you want when it's done.
That's it. No machines. No fancy ingredients. If you use semi-skimmed or skimmed milk, it still works apparently (I've not tried that yet, but endeavour to), just the yogurt is a little more runny due to the lesser fat amount.... and the way the store bought yogurt deals with that is thickeners... you can probably just add some milk powder if you really need thicker yogurt.