The answer should be quite straightforward: “Cheese is milk which has been concentrated and preserved.” Preservation is, in a nutshell, the slowing down of the natural progression of putrefying organisms. In natural cheese-making one uses the following scientifically and historically sound methods of preservation:
Extraction of Moisture
All organisms have a minimum required moisture intake necessary for survival. This requirement will increment relative to the energy used. Whilst a micro-organism is reproducing it will use more energy thus, by making less moisture available we restrict it’s capability to reproduce, or even to survive at all if we so wish.
Removal of Energy Sources
In milk, the main energy source comes in the form of lactose (milk sugars). The lactose is dissolved in the water content of milk. If we reduce the moisture we also reduce the available energy.
The lactose is used mainly by the acid producing “starter” bacteria so, by encouraging the growth of these we reduce the lactose available to spoilage organisms.
All organisms have an optimum acidity at which they will operate best. By controlling the acid production we, again, control the spoilage organism’s survival and reproductive capabilities. We also control the actions of desirable organisms of course.
Salt inhibits the energy uptake of bacteria. The tolerance to salt will depend on the individual species of the bacterium and will vary from one species to another. The amount of salt used in cheese-making will depend on the type of cheese and the organisms that we wish to restrict. Salt is not used simply as a flavor enhancer.
Unfortunately, the answer is nowadays not so simple. Large-scale cheese production includes the use of a mind-boggling array of additives and preservatives. In Britain today at least 75% of home production contains genetically modified material via G.M rennet. I would expect the percentage to be somewhat higher in the U.S.
Often the justification for genetically modified food production is that it helps to feed under-developed third-world countries. The other side of this argument is that it has lead to extreme unemployment in the agricultural sector. Smaller scale production would give us better quality and safer food and also a better quality of life for many.