I do actually own a yoghurt maker, which was a gift from my parents. It’s a nice round contraption with cute little jars which make great individual serving sizes, and it keeps a constant temperature so a great guarantee of consistent results, and super-handy in winter time. The little jars are a bit of a faff to sterilise though, and at the moment I’m going through a lot of yoghurt because I like to use it as a salad dressing mixed with vinegar, smoked paprika, garlic and hot sauce, so I thought I’d try something new.
UHT soya milk is already sterile, so no need to scald it then wait for it to come down to temperature (110-115F), instead I got a large stock pot (also a gift from my folks!) and filled it 3/4 full of warm water. I got the temperature to around 120 degrees and then stood two sealed litre cartons of milk in the pot (one Value and one Organic one I had left over from when they were on offer for 59p!) and left them for 20 minutes to warm through. I then opened them up and tipped some of the milk into a glass for later (to make a bit of room in the cartons), and tipped a bit more into a measuring jug. I mixed about 6 heaped tablespoons of live plain soya yoghurt into the milk in the jug, and them poured half into each carton, sealed them well up and stood them up in the water bath, which came to just below the tops of the cartons.
The temperature had dropped to just below 110 degrees when I put them back in, but I just put the gas on a low heat underneath until they’d come up to 115, then draped a folded bath sheet over the top and sides. The volume of water kept a good heat (I think it being a warm day probably helped too), and after 7 hours I had yoghurt! It’s a bit lumpy, but I’m just going to be mixing it up with other stuff so I don’t care.
One concern I had (after I’d started making it) was that the cartons tell you to store them in a “cool, dry” place, which the stock pot most definitely was not! I started worrying that the plastic lining of the cartons wasn’t designed to be heated, and would leach harmful bits of itself into my yoghurt, and when I tried to find information on how safe Tetra Paks are to heat food in it was surprisingly difficult, however I did find something assuring consumers that they’re designed to withstand heat such as being left in a hot car, and a car’s interior can get well above yoghurt making temperature in the summer so it looks like it’ll be okay! 🙂