|MadSci Network: Microbiology|
This is an excellent question. Two key factors which influence the growth of all microbes (bacteria, mold, yeast) are pH and water activity (or available water). Water activity is not the same as water content, but they are related. In keeping with this, high moisture cheeses will generally grow mold faster, so very hard cheeses like parmesan will take a long time to mold, cheddars will be faster, mozzarella faster still, and ricotta or cottage cheese fastest of all. Now this assumes pH differences between these cheeses do not play a role, but in reality they might. For a related discussion of cheese safety, see my presentation "Say Cheese" here: http://www.foodsci.rutgers.edu/schaffner/presentations.htm. Note that this is a technical presentation, written for adults, but it does give pH and water activity values for many cheeses. Your parents and teachers may be able to help you with understanding the more difficult parts. Other information you will need to think about for your experiments: (1) Some mold is toxic - be careful, ask teachers or parents for advice. (2) Mold can't grow unless it's spore are present, and not every package you buy at the store may contain spores. Will you rely on naturally occurring mold or will you add some yourself? (3) If you add some yourself, where will you get it? Moldy bread? (4) If you rely on natural contamination, how will you be sure that all your samples have equal contamination? (5) Some cheese already contains mold... Blue cheese is blue from mold! (6) Don't forget, some mold is toxic - be careful, ask teachers or parents for advice. Good luck and happy experimenting!
Try the links in the MadSci Library for more information on Microbiology.