Alkaline phosphatase is an enzyme naturally produced by mammary cells and present in cow's milk. The concentration of alkaline phosphatase can vary based on feed, season, breed of cows, stage of lactation, and milk yield. Alkaline phosphatase is inactivated at a higher temperature than the usual temperature of pasteurization. Decreased activity of alkaline phosphatase can therefore be used to determine that milk was pasteurized properly and that the pasteurized milk is not contaminated with raw milk. Alkaline phosphatase is able to cleave phenolphthalein monophosphate releasing phenolphthalein. Hardy Diagnostics Alkaline Phosphatase Kit is based on the Rutgers method, which is a stable and sensitive method that provides an easy to interpret color read out within 30 minutes.