There are three main categories of cheese in which the presence of mold is a significant feature: soft ripened cheeses, washed rind cheeses and blue cheeses.
Soft-ripened cheeses begin firm and rather chalky in texture, but are aged from the exterior inwards by exposing them to mold. The mold may be a velvety bloom of Penicillium candida or P. camemberti that forms a flexible white crust and contributes to the smooth, runny, or gooey textures and more intense flavors of these aged cheeses. Brie and Camembert, the most famous of these cheeses, are made by allowing white mold to grow on the outside of a soft cheese for a few days or weeks. Goats’ milk cheeses are often treated in a similar manner, sometimes with white molds (Chèvre-Boîte) and sometimes with blue.
Washed-rind cheeses are soft in character and ripen inwards like those with white molds; however, they are treated differently. Washed rind cheeses are periodically cured in a solution of saltwater brine and other mold-bearing agents that may include beer, wine, brandy, and spices, making their surfaces amenable to a class of bacteria Brevibacterium linens (the reddish-orange “smear bacteria”) that impart pungent odors and distinctive flavors. Washed-rind cheeses can be soft (Limburger), semi-hard (Munster), or hard (Appenzeller). The same bacteria can also have some impact on cheeses that are simply ripened in humid conditions, like Camembert.
So-called blue cheese is created by inoculating a cheese with Penicillium roqueforti or Penicillium glaucum. This is done while the cheese is still in the form of loosely pressed curds, and may be further enhanced by piercing a ripening block of cheese with skewers in an atmosphere in which the mold is prevalent. The mold grows within the cheese as it ages. These cheeses have distinct blue veins, which gives them their name and, often, assertive flavors. The molds range from pale green to dark blue, and may be accompanied by white and crusty brown molds. Their texture can be soft or firm. Some of the most renowned cheeses are of this type, each with its own distinctive color, flavor, texture and smell. They include Roquefort, Gorgonzola, and Stilton.