The purpose of this experiment was to determine whether skim milk or whole milk turns sour first. This was determined by finding the pH of the whole milk and the skim milk every twelve hours or until the pH drops. To carry out his experiment five trials were conducted. 250 milliliters of the whole milk, skim milk and distilled water were poured into five cups each. The whole milk, skim milk and distilled water were left out at room temperature for five days. The pH was tested every twelve hours until both the skim milk and whole milk's pH dropped to five. The whole milk's pH dropped first, then the skim milk's pH dropped. The water remained at a pH of six for five days.

Skim milk stays fresh longer than whole milk because of the amount of lactose in whole milk. Whole milk contains more lactose than skim milk. When bacteria turns the lactose into lactic acid, the milk turns sour and curdles. The more lactose the milk has, he more nutrients the bacteria has to thrive. Therefore more lactic acid is formed and when lactose is turned into lactic acid the milk turns sour and curdles. It is important for milk consumers to know these results, so they can chose whether they would prefer a kind of milk that stays fresher longer. Who wouldn't want their milk to stay fresher longer?