What is Pasteurization?

Louis Pasteur was a famous scientist.  As you know when you leave milk out it spoils.   When Pasteur was alive, people thought that certain cows were more likely (than others) to cause milk spoilage because they produced an inferior type of milk.  However Pasteur thought it might have to do with bacteria.  He set up an experiment where he used two glasses of milk. In one of the glasses he added boiled milk.  He discovered that the boiled milk did not spoil as fast as the un-boiled milk. He told his colleagues; and when his colleagues tried the experiment, they got the same results.

1. What was the problem for Pasteur?
2. What do you think was his hypothesis?
3. What was the manipulated (independent) variable?
4. What was the dependent variable he measured?
5. Which group was the control:  the boiled milk, or the unboiled milk. Explain.