Since it crops up quite a lot (and since most of the yoghurt in the supermarkets is now "low fat") I thought I'd mention my Greek yoghurt recipe again.
Greek yoghurt is just strained yoghurt. Yogurt is just milk fermented at 35-45'C. Technically Greek yoghurt has a certain mix of bacteria, and I've tried making it with various different sorts of starter - including Greek and Turkish - but I honestly can't taste the difference. Any starter will do. It's the straining that has the biggest impact on flavour and texture.
So, you need something that keeps the heat stable, and something to strain with. I use a toaster oven and a piece of fine cheesecloth, but I've also used a thermos-type container, and that works fine too.
- Take a litre of full-fat milk and pour it into a microwaveable container. I use an earthenware pot because I can just put that straight in the oven (see below). Better-quality milk makes better-quality yoghurt.
- Microwave it on high until it's somewhere between 40 and 45'C. If you don't have a thermometer, just taste it - when it's pleasantly warm, but not hot enough to make a hot drink with, it's done. Takes 2-3 minutes in an average 800W microwave. Stir once or twice to maintain even heating.
- Mix in 1-2 tablespoons of fresh, live yoghurt (it will say "live cultures" on the pot). These are quite hard to find among the fakes and low-fat offerings, but most supermarkets carry at least one brand.
- If you're using a thermos, you have less leeway with the microwaving process - make sure it really does reach 45'C, and goes no higher than 48'C. Let it cool to 45-46'C if necessary. Then add the starter and pour into the thermos.
- If you're using a toaster oven, do an experiment beforehand to maintain a pot of water at around 40'C, and mark the appropriate position on the dial. Again, you can just taste-test if necessary. Most toaster ovens can do this, but they don't have a mark for that low temperature, so this is very much a trial-and-error thing. Use a heavy pot to smooth out the temperature variations inside the oven due to the on-off thermostat action. We're aiming slightly lower than 45'C to avoid any potential culture die-off from short excursions up to 50'C.
- Leave it there for 6-10 hours. It's done when it looks like blancmange. The timing isn't really important, although longer times tend to produce a more tart result.
Put your cheesecloth into a colander or a large sieve, and suspend it over something to catch the runoff (or just put it in the sink). Pour the yoghurt in. It's done when it reaches the desired texture, but you should find roughly 40% of it runs off as liquid, which takes an hour or so. Spoon out the yoghurt and put in a clean container.
Make sure all your equipment is clean! You don't need to sterilize stuff, but a good rinse with boiling water is sensible.
Tip: you'll get a somewhat milder flavour, and a creamier texture, if you use UHT milk. You can achieve a similar effect by heating the milk to about 90'C and then letting it cool.
It sounds complicated, but it's literally a few minutes in the kitchen once you get used to the procedure. I make a batch every 3-4 days, so I've always got some in the fridge.
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