器具:Thermometer, pots, a cooler, glass jars, and a measuring cup.
Sterilize: put jars in a pot filled with 1" of water, boil for 15 minutes, leave them in the pot until needed.
Heat milk slowly in a pot to 85-90℃ (185-195F). Then cool the pot of milk in a pot of water to 50-55℃ (122-130 F).
Mix 250ml of warm milk with the yogurt thoroughly. Then pour the yogurt-milk mixture back into the warm milk, mix well.
Pour the yogurt-milk mixture into the sterilized jars and cover them with lits.
Place the jars into a cooler. Then put a bowl of boiling water into the cooler with the jars to keep the cooler warm.
Wait for 3 hours or until the yogurt has gelled. Put the finished yogurt into the fridge.