A newborn is usually salty-yet-bland in flavor and, for harder cheeses, rubbery in texture. These qualities are sometimes enjoyed — cheese curds are eaten on their own — but usually cheeses are left to rest under carefully controlled conditions. This aging period (also called ripening, or, from the French, affinage) can last from a few days to several years. As a cheese ages, microbes and enzymes transform its texture and intensify its flavor. This transformation is largely a result of the breakdown of casein proteins and milkfat into a complex mix of amino acids, amines, and fatty acids.
Some cheeses have specific bacteria or molds intentionally introduced to them before or during aging.
The blue cheeses (Roquefort, Stilton, Gorgonzola): Penicillium mold is added to the curd before molding. During aging, the blue molds (Penicillium roqueforti or Penicillium glaucum ) grow in the small fissures in the cheese, imparting a sharp flavor and aroma. The same molds are also grown on the surface of some aged goat cheeses.
The soft cheeses Brie and Camembert, among others, get a surface growth of another Pennicillium species, the white-colored Penicillium camemberti. The surface mold contributes to the interior texture and flavor of these small cheeses.
Some cheeses are periodically washed in a salt-water brine during their ripening. The salty environment nurtures the growth of the Brevibacterium linens bacteria, which can impart a very pronouncedodor (Limburger) and interesting flavor. The same bacteria can also have some impact on cheeses that are simply ripened in humid conditions, like Camembert. Large populations of these "smear bacteria" show up as a sticky orange-red layer on some brine-washes cheeses.
