While it may seem obvious, cheesemaking starts with milk. High quality, fresh milk is key to making any cheese. Cheesemakers agree that unpasteurized milk produces the most high-quality, delicious cheeses. Also known as "raw" milk, care must be taken when transporting the unpasteurized milk to avoid its contamination. The pasteurization process in which milk is heated to remove bacteria and germs, can sometimes affect the enzymes of the cheese. It impacts the ability of cheese curds to form, as well as the taste of the final product. If you don't raise cows, goats or sheep, or live near people who do, unpasteurized milk can be difficult to procure. In that case, any type of milk may be used to make cheese. This includes whole, 2% or skim milk.
In the cheesemaking process, milk proteins, or "caseins," are transformed into curds, forming the basis of cheese. This is done by the addition of a "starter culture" to milk which transforms the lactose found in milk to lactic acid. Starter cultures are typically a bacteria. The bacteria undergoes a process that can be compared to the way yeast is used in brewing beer. There are several types of starters used in cheesemaking. The type of cheese you're making determines the best starter culture to use. For example, some starers are ideal for making mozzarella, while others are better suited to feta or camembert. Starter cultures help determine the flavor and texture of the finished cheese.
In serious cheesemaking, when the pH is at the proper level, animal or vegetable-derived rennet is added to the mixture. Rennet is an enzyme that works with the starter culture to transform the mixture into curds. This is essentially the "curdling" of the milk. Typically, the larger the curd, the softer the cheese. At this point, the cheese can be concentrated in a number of ways, such as by salting or pressing into a mold. Cheeses such as gruyere, require that the curds cook further. Fresh cheeses, such as ricotta and cottage cheese, are ready to eat at this point.
To make a firmer, aged cheese such as cheddar, the curds need to ripen. The ripening process has many factors such as time, temperature, humidity, bacteria and salt. During this process a mold may form which you'll recognize as the rind of a cheese.
The influences of milk, starter cultures, rennet and the concentration process all help determine the taste, smell and look of a finished cheese. There are many established best practices in cheesemaking to help you create your ideal cheese. However, once these general concepts are understood, there is ample opportunity to experiment. The fascinating cheesemaking process rewards patience and attention to detail, but is a fun and rewarding experience.