Milk like most other foods that we can consume allows the growth of micro-organisms that use the nutrients in milk and in many cases are harmful for our health. To extend the useful life of milk it is pasteurized. But just pasteurization alone does not allow the milk to be stored at any temperature. The rate of growth of harmful bacteria increases as the temperature at which the milk is stored is increased.
Milk can be safely stored for up to two weeks if the temperature it is kept at is close to 32 F. Harmful bacteria cannot grow in milk when the temperature it is kept at is below 45 F.
At higher temperatures, the rate of growth of harmful bacteria is very fast. It has been observed that with every 18 F increase in temperature above 45 F, bacteria grow at twice the rate.
To design your report you could keep the milk exposed to the environment and at different temperatures. Record how long it takes for the milk to get spoiled, this can be inferred from the milk splitting.