It's easy to follow the directions on the recipe, but what's going on? The science of food is where the magic happens. There are many great references (one of my favorites if you want to get to the fundamentals of what is going on is Food Science from Guelph University), on the complex nature and reactions of milk and dairy products but here are some key points:
Start with the milk. Using cow's milk as an example. It a blend of 3.3% proteins, 4.6% sugars and 3.9% fat in water with various minerals - so about 12% - 13% solids.
Of special interest for the moment is that the sugars are mostly Lactose and the Protein mostly Casein.
The art of making cheese, yogurt and a whole world of other products is how this process is manipulated and fine tuned. How quickly this all happens, how completely, how much sugar is left and how much acid, how it is aged.... Just like wine, cheese is a natural product and once we start the ball rolling with bacteria they will eat what they can until you stop them or they run out of stuff to eat or die. Each will produce specific byproducts that will have taste and smell and texture.
The art is in how this is managed - one path leads to Yogurt the other to Camembert....but it all started with milk.
Like most things - the biology and the chemistry of these every day events are a wonder.
Adventures in Cheesmaking
This all started out as a curiosity. Like most stuff we eat there is a rich history behind it. Centuries of experimentation. Cheese is just another example.
From the horse back tribes of the Asian Steppes to the Silk Road camel caravans to Romans Legions to European Monks to today, milk was a great source of nutrition but spoiled quickly and was heavy to transport.
The answer was cheese.