Question: Why do the directions on the package of yogurt culture say to add three tablespoons of dry milk powder to each liter of milk before heating for a firmer yogurt? I’ve noticed that some other recipes give similar advice, too. But, the directions on your website say to use just milk and yogurt culture. In fact, you explicitly state, “No other added ingredients!”
Jerri’s answer: You can add dry milk powder if you want, but there’s no need to. Your yogurt will come out thicker if you incubate it longer.
Yogurt can come out less thick if you don’t thoroughly mix the culture throughout the milk. When that happens, you get a runny layer near the top and thicker yogurt underneath…or even the exact opposite. All you have to do is mix the two layers together and refrigerate, and it will thicken.
One tip for getting a good mix is to sprinkle the dried yogurt culture on top of the warmed milk and let it sit there until it dissolves. This usually only takes about a minute. Then, mix thoroughly. If you start mixing before it dissolves, the dried culture can clump, and then you won’t be able to mix it in thoroughly.
Another reason why your yogurt might not thicken properly is because it didn’t incubate long enough at 105° F. In other words, the temperature decreased too quickly. You need to find a warmer place to keep your incubating yogurt.
And then, of course, using milk with less milk fat, like lowfat 2% milk, will yield a thinner yogurt. The same thing happens with raw milk if the cream has been skimmed off the top.