Yogurt is made into a sour ingredient by using a live sour culture when making the yogurt. As the yogurt sours, it starts to develop small beads of water on the surface of the yogurt. Increased amounts of water indicate an increase in the intensity of the sour flavor. As the yogurt reaches the desired level of sourness, which can be determined by tasting it, place the yogurt in the refrigerator to maintain the desired flavor and intensity.