Line a colander with a large cotton towel or double thickness of cheesecloth, and place the colander in the sink. Add 6 cups low-fat plain yogurt. Let stand for 15 minutes then place the colander over a bowl. Cover with plastic wrap and refrigerate for 24 hours. Gathering the edges of the towel together, gently squeeze out any remaining liquid. Transfer the yogurt cheese to an airtight container. Makes 2 cups. Cover and chill for up to 1 week.