A Staff Report from the Straight Dope Science Advisory Board

What makes blue cheese blue?

November 9, 2004

Dear Straight Dope:

What kind of cheese is blue cheese without the blue? Does it develop from the beginning or is it a type of cheese that gets moldy?

Your suspicions are correct, DB. Blue and blue-green cheeses can be made from most cheese bases, whether the milk is from a cow, sheep, or goat. The main thing that makes a blue cheese blue is mold.

Cheese making generally consists of three basic steps. The first step is precipitation of the milk into curds, the second is concentration of the curds and removal of the whey by pressing and draining, and the third is aging or "ripening." The purpose of ripening is to allow bacteria and other microbes to act on the curds and transform them into the final product. It's during this last step that an ordinary cheese can become a blue cheese, using a blue-green mold such as Penicillium roqueforti. This mold grows within the cheese and breaks down complex organic molecules into simpler ones, smoothing out the fibrous structure of the cheese and providing the sharp flavor and smell associated with blue cheeses.

Blue cheeses were originally a product of the environment in which they were ripened. In the case of Roquefort, the Roquefort caves in which the cheese was stored were teeming with Penicillium roqueforti.  The circumstances surrounding the discovery of Roquefort are the subject of legend and history. The earliest legend has it that a shepherdess left her lunch of cheese curd and rye bread in a cave, and when she returned to find it weeks later, she discovered Roquefort cheese. The Roman historian Pliny (23-79 AD) wrote of a cheese from a mountainous region of France near the Mediterranean that might have been Roquefort, and it is reputed that even Charlemagne himself was served Roquefort at the monastery of St. Gall in 778.

Here's how Roquefort cheese was originally made:

The farmers would collect the milk, curdle it with rennet, then scoop the curds by hand into molds. A powder made from grating moldy bread was sprinkled into the curds . . . The bread was stored in the same damp caves that aged the cheese, and in a few weeks it turned blue and was ground to dust for cheese making (reference 1)

The name Penicillium roqueforti sounds like penicillin because it's related to the common and useful antibiotic mold. This relation is more than just skin-deep, as blue ripened cheeses do seem to inhibit the growth of harmful (and other) bacteria, such as Clostridium and Staphylococcus. However, lest you think that eating lots of Roquefort will clear up that nasty infection, know that most cheeses contain relatively small levels of antibiotic mold relative to that found in concentrated pharmaceuticals.

In modern blue cheese production, the mold comes from a highly controlled "starter" batch. For home made blue cheese, the mold is taken from the previous batch of cheese. This mold is introduced into the ripening cheese by poking long skewers through the mixture, which also allows air introduced to assist in the mold growth. However, to maintain a quality product with a consistent look and feel, some modern production methods mix the mold with the curds before they're pressed, so no skewering is involved. While cheese purists are divided somewhat on which technique produces a better cheese, I can find no evidence of a preference in the consumer market.

Blue cheese making is a serious business, so much so that the names of some blue cheeses are legally protected. Roquefort, for example, has been protected by a French crown patent since 1411, when it was declared that "only the cheese of Roquefort-sur-Soulzon could be called Roquefort cheese" (1). French cheese makers generally don't risk uncertain quality control by allowing their cheese to acquire its mold from the Roquefort cave air and soil, and instead use a starter like most cheeses. English Stilton cheese, another blue cheese, is also protected by legal trademark and has been declared a "protected designation of origin" by the European Union, and thus can only be legally made and branded as Stilton in the counties of Derbyshire, Leicestershire, and Nottinghamshire in England. Maytag blue cheese was originally invented by Fritz Maytag, son of the founder of the appliance company, working in conjunction with Iowa State University. Thankfully, Maytag blue cheese production does not require aging the cheese in a washing machine, nor that a friendly Maytag repairman be involved in the cheese making process. Although he's a nice enough fellow to ask around for tea.


(1) "Salt, A World History" by Mark Kurlansky, 2002

(2) "On Food and Cooking" by Harold McGee, 1984

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