Lactose. Polarised light micrograph of crystals of the sugar lactose found in milk. It has the chemical formula: C12. H22. O11. Lactose is a white sugar occurring in solution in the milk of all animals. Human milk contains 6% lactose; cow's milk contains 4%. It is commercially prepared by evaporation of the whey obtained in cheese-making. Like table sugar (sucrose), it is a disaccharide consisting of two basic sugar units: glucose and galactose. Unlike sucrose, however, lactose is tasteless. Magnification: x63 at 35mm size.