Yogurt is easy and cheap to make! Scald on quart of milk on the stove top to kill all bad bacteria. Pour the hot milk into a large mayonnaise jar and cool to 112 degrees. Maintain the temperature of 112 degrees in your oven, and add a small container of plain commercial yogurt to the warm milk. Stir the mixture thoroughly. Keep the Mixture in the oven at 112 degrees for four to ten hours. The longer the yogurt is left, the tarter the yogurt. A small amount of this yogurt can be used to start the next batch.