In making your own yogurt, add half (1/2)c. nonfat dry milk to a quart of milk (homogenized). Heat the milk to boiling. It should be a rolling boil, not just a simmer. Cool it to 115 degrees F. (when drops of milk on inside of wrist feels warm). Mix half (1/2) c. of this cooled milk with 2 Tbsp. commercial yogurt and stir until smooth. Then add mixture to remaining milk. Pour it into the container you are going to eat it from. Put these on a tray and set in a warm place where it will not be disturbed which could break the curd. Let it stand overnight or until it has set. Refrigerate the coagulated yogurt until used. Save 2 or more tablespoons of the yogurt to repeat the process.