Once all the powdered milk is blended into the warm water stir a heaping spoonful of yogurt into the milk mixture. For some reason it isn't a good idea to use the blender to mix in the yogurt, too violent? I've tried it and for some reason gentle stirring is better. Put the pan of incubating yogurt in a warm place. I'm showing using a "cooler" with a couple of mason jars of very hot water. I'll close the lid and leave it there for eight hours and will have yogurt. The idea to to keep it warm for 8 hours, you could use the top of the water heater, a heating pad, an oven with a pilot light, anyplace where it stays consistently warm for several hours. It can stay there from 8 to 12 hours. I wouldn't leave it any longer than that.