Bacteria's role in cheese making is important. Those little creatures that sometimes give us infections are also friendly at other times, we know - just how friendly is about to be shown, as I talk about two of my favorite things in the world: bacteria and cheese.
The two main kinds of bacteria used for making cheese are varieties of Lactococcus, which used to be called Streptococcus, and varieties of Lactobacillus. The difference between them is that Lactococcus is a mesophilic bacterium, meaning it likes cooler temperatures (room temp is good), while Lactobacillus varieties tend to like hotter temperatures, and are called thermophilic.
The differences between the kinds of bacteria used in cheese making are what define how many kinds of cheese exist. Lactococcus is a huge strain, as is Lactobacillus, and every kind of each of them is used somewhere in the world to create cheese. Lactococcus has a huge range with regards to the cheese it can make. For instance, varieties of it can make cheddar cheese, colby, feta, or any semi-soft cheese, depending how the application comes across, but also havarti or gouda. Lactobacillus, on the other hand, will make gruyere, a mountain cheese. It should be noted here that if you want a very hard cheese like parmesan, youn need to use streptococcus thermophilus.
Just by looking at that, a pattern should be starting to show: very specific kinds of cheese go with certain bacterial groups. This is true for yogurt as well, which is often used in cheese making courses as the precursor to learning to make cheese. But bacteria are not the only little creatures used to make cheese; blue cheese requires fungi for instance. However, bacteria produce the most different kinds of cheese in general. There are actually an unknown number of the kinds of cheeses, because people are constantly coming up with new ones and new bacteria are always being used.
In both mesophilic and thermophilic bacteria, cheese is made by their fermenting whatever sugars they find. This is exactly what they'd do in the wild; take sugars and ferment them - though in that case, they would end up with energy. Doing it in the cheese mixture helps to solidify the cheese, and makes it taste better - just like a lot of wines do when they are aged. There are also bacteria who grow after the cheese has been allowed to sit, while it is sitting, in fact. This ages the cheese further. In general, the longer a cheese is allowed to sit with those bacteria roaming around inside it, multiplying and eating up any sugars they find, the better it will taste. This is why ricotta and other quick-to-make cheeses have a sweeter taste; the bacteria that were put in them wasn't there for long.
So here we've seen a bit about the role bacteria plays in making cheese. That wasn't so scary. I'm going to go have some gouda now.