* Special hint To make yogurt at home, an active (living) yogurt culture is needed as a starter. Commercial, unflavored cultured yogurt, from the supermarket is usually used as a starter. Yogurt starter cultures can also be purchased at health food stores, but are quite expensive compared to commercial cultured yogurt. Once you start making yogurt at home, save some of your homemade yogurt to start your next batch. For best results, however, purchase commercial cultured yogurt to replenish a homemade culture every four to five batches. For thick, firm yogurt, place cold, pasteurized milk in the top of a double boiler and stir in nonfat dry milk powder. Stir in sugar or honey if sweeter, less tart yogurt is desired. Sprinkle gelatin over the milk. Let stand for 5 minutes to soften gelatin. Heat milk to 200 degrees F and hold for 20 to 30 minutes, stirring gently to dissolve gelatin. Continue from Step 3 under thin yogurt.