Put 2 cups of milk in a quart jar. Cover with a double thickness of cheesecloth and secure it with an elastic band. Let stand at room temperature for 24 hours. Blend in 2 cups of whole wheat or unbleached white flour, mix well, replace the cheesecloth and let stand, preferably outdoors, in a warm place until the mixture is very bubbly. Water can be substituted for the milk, thus eliminating the first 24 hours of this process but milk give the mixture a special flavor. Put the mixture into a container that allows room for expansion. Keep covered in the refrigerator. When the starter is used it should be replenished with equal amounts of milk or water and flour. This mixture should be used and replenished every week. If you do not bake regularly pour out half the starter and replenish it with fresh water or milk and flour every week.