Ordinary, but skimmed milk - mumsnet says you need to boil it for ~10 mins and then let it cool to ~40C before adding the live yoghurt culture. Working well so far!
UHT is usable, and doesn't need to be boiled, but for that added convenience it costs nearly twice as much.
UHT is usable, and doesn't need to be boiled, but for that added convenience it costs nearly twice as much.