Does soy milk contain the same sugar as cow's milk? Extract lactose (milk sugar) from three types of milk and weigh what crystallizes out. You heat low-fat milk, powdered milk, and soy milk with acetic acid to remove the protein. Then you add ethanol to the remaining liquid and let it cool slowly. As each solution cools, lactose crystals form at the bottom. Weigh the crystals from each type. Fresh and powdered milk yield nearly the same amount, but soy milk produces almost three times less.