Fresh milk has a pH value that is typically between 6.5 and 6.7, making it slightly acidic. A pH greater than 6.7 indicates that the udders producing the milk are inflamed by pathogens, and milk with a pH lower than 6.5 indicates heavy bacterial action and milk spoilage.
The pH number of a solution is inversely proportional to the concentration of hydrogen ions present. Acids release hydrogen ions and have a lower pH, while bases accept hydrogen ions and have a higher pH. Milk is composed of 87 percent water, but its acidity originates in the milk proteins present. The milk proteins and the milk salts allow milk to act as a buffered solution, meaning it resists changes in hydrogen ion concentration, keeping the pH value to a narrow range.