I picked up 211 Things a Bright Girl Can Do at a book sale. The first bright thing described is making yogurt in a Thermos flask. I'd type it out for you, but you can Google 'make yogurt in a Thermos' and get loads of suggestions about types of milk (don't use UHT; I used semi-skimmed), whether to add powdered milk (haven't tried it yet), etc. I basically heated milk to boiling, let it cool (using a candy thermometer to measure the temperature), added yeast I bought from Amazon, poured it into the clean, pre-heated Thermos and wrapped it in some bath towels. The yeast packet said to check that it was setting at 10 hours, so I did; it said it might need to set up to 36 hours but mine was fine after 24. I poured it into jars and put them in the fridge for a few hours and we've eaten it all week.
I gather I can save newly homemade yogurt in the freezer to use in place of the bought yeast. That is an experiment for another day. Meanwhile, I found some store bought yogurt in the deep freeze. When we are away for more than a few days I tend to throw a lot of things into the freezer to use later. As with many things, freezing seems to change the texture of yogurt and of course it separates more than usual. Sometimes a good stir is all that's needed, but I found that straining the thawed yogurt gave me some creamy low fat spread for crackers or bread (much healthier than margarine, pate or hard cheese) and a bit of whey. We were out of bread the next morning so I whipped up some muffins from the 'universal recipe' in the Tightwad Gazette and used the whey as part of the liquid component.
Have you made your own yogurt?