Making cheese

The artful transformation of milk into cheese occurs in three stages: In the first stage, lactic acid bacteria convert milk sugar into lactic acid. The second stage involves the addition of rennet and the subsequent curdling of the casein proteins and drainage of the watery whey from the concentrated curds. The third stage is ripening. Protein and fat-digesting enzymes present in the milk, from the bacteria and molds, and from the rennet work together to create the unique texture and flavor of the cheese.

Nearly all cheeses are curdled with a combination of starter bacteria acid and rennet. Acid and rennet give different curdle structures. Acid yields a fine, fragile gel; whereas rennet produces a course but robust, rubbery one. Fresh cheeses and small, surface-ripened goat cheeses begin with predominantly acid coagulation. Large semihard and hard cheeses curdle in rennet-dominant coagulation. Cheeses of moderate size and moisture have moderate content of both.

After curdling, the excess water is drained from the curds. For soft cheeses, whole curd is allowed to drain by gravity alone for many hours. The curd of future firmer cheeses is precut to increase surface area and is actively pressed to expel more moisture. Cut curd may also be cooked in its whey to 130° F/55° C to further expel whey and encourage flavor production by bacteria and enzymes. All cheese is later placed into molds and pressed to its final shape and moisture.
Salt is added to new cheese either by mixing it with the curds or applying dry salt or brine to the whole cheese. In addition to taste, salt inhibits the growth of spoilage microbes and acts as a regulator of cheese structure and the ripening process. Salt draws moisture out of the curds and firms the protein structure. Most cheeses contain 1.5 to 2% salt by weight.

Ripening, or affinage, refers to the process of bringing cheese to the point at which flavor and texture are at their best. Cheeses are said to be alive. They begin young and bland, mature into fullness of character, and eventually decay into harshness and coarseness. The length of vitality depends on the type of cheese. The cheesemaker manipulates the maturation process by controlling the temperature and humidity. Specialist cheese merchants in France are also affineurs; they buy freshly made cheese and carefully mature it in their own premises to sell at their best. Industrial producers ripen their cheeses only partly, then refrigerate them to suspend their development before shipping. This technique maximizes shelf life and stability though quality suffers greatly.