Well, unlike the gravy the talented Mr Kelly sings of, anyone can make homemade yoghurt... providing you have a thermos or other temperature controlled capsule to keep it in while the cultures do their thing. I first started making yoghurt myself after reading Julie's post on it at Towards Sustainability - and I do love it when other people have done all the research for me! I played around with her methods, and have perfected my own method to come up with a consistent yoghurt of just the right texture and flavour for us.
I use an Easiyo thermos. I used to use the Easiyo sachets, but wanted a recipe that was more sustainable and contained less additives. Here is how I do it.
Ingredients (for first batch)
1 litre UHT milk
4 tablespoons powdered full cream milk (this thickens the yoghurt - I like mine thick and pot-set)
2 - 4 tablespoons biodynamic plain yoghurt (make sure it does not contain gelatine; most biodynamic yoghurts don't. I used Jalna - with the yellow lid)
Mix the yoghurt and the powdered milk together with a bit of the UHT milk until smooth. Add the rest of the UHT to the mixture in an Easiyo container and mix well. Pour boiling water into the Easiyo thermos to the recommended point and insert the container. Seal and let it sit for 14 hours (overnight). If set in the morning, refrigerate.
For continuing batches of yoghurt, keep two to four tablespoons of the previous batch to 'seed' a new one.
Scientifically speaking (and this is not a strong point of mine) using an Easiyo themos and UHT milk negates the need to meticulously pre-heat the milk to a particular temperature in order to kill off the 'bad' bacteria. UHT is already heat treated, and the thermos keeps the temperature steady for long enough for the yoghurt to form.