Mould in Cheese

An old legend has it that Roquefort cheese was first discovered by a shepherdess who left her cheese curd and rye bread lunch in a limestone cave. When she returned several weeks later she found the cheese had developed a mouldy bluish colour and a pungent taste.

Whether the shepherdess’s story is folk tale or fact, the very first blue-mould cheeses were indeed simple products of their environment. In the case of Roquefort, the damp, airy caves found in the village of Roquefort-sur-Soulzon were naturally teeming with Penicillium mould. When cheeses were stored in the caves, the mould took up residence in them, giving the curd a creamy texture, piquant flavour and bluish-green mottling that is now famous.

How Does Mould Work?

The moulds used in cheese production are common moulds that are widespread throughout nature. As types of fungi, they belong to the same family as mushrooms and yeast. They also share many characteristics with plants. But unlike plants, moulds do not make their own food through photosynthesis. Instead, they produce special enzymes that work to break down and absorb organic substances. When used in blue cheese production, these enzymes literally eat away at the cheese, turning complex molecules into simpler ones. As a result of this mould process, the fibrous structure of cheese is transformed into a more creamy-crumbly texture, and the sharp flavour and assertive aroma we know and love are created.

Modern Production

The moulds most commonly used in modern cheese production include Penicillium roqueforti, Penicillium glaucum and Penicillium camemberti. It’s interesting to note, as relatives of the antibiotic penicillin, these moulds also work to restrict the growth of harmful bacteria (Clostridium, Staphylococcus) within the cheeses they produce.

While mould has been an ingredient of Roquefort, Gorgonzola, Stilton, and other blue cheeses for centuries, modern cheese makers generally no longer rely on floating mould spores in limestone caves to ripen their cheeses. Because consistency and quality are of the utmost importance in the present-day market, mould use has to be more closely controlled. This can be accomplished using two different methods.

In the first method, pressed cheese curds are inoculated with skewers of mould during the closely monitored ripening process. This allows air to enter and assist mould growth as the cheese ages. In the second method, a Penicillium mould is mixed with the cheese curds before they’re pressed. With this process, no skewering is involved and the cheese maker is assured his cheeses will have a very consistent look and feel.

Surface-Ripened Cheeses

While most of our attention has been focused on the great blue-veined cheeses, moulds also play a role in producing creamy-rich, white cheeses such as Camembert and Brie. Known as surface-ripened cheeses, mould works here to ripen the cheeses from the outside in.

With Camembert, Penicillium camemberti may be mixed with the milk, sprinkled on the curd, or skewered or rubbed into the cheese during ripening. As the cheese cures, the mould develops into a thin, greyish, outer rind. While the mould growth does not penetrate the cheese, the enzymes do infuse the interior, creating Camembert’s characteristic semi-liquid interior.

Brie, which is similar to Camembert, is surface-ripened with inoculations of Penicillium camemberti or Penicillium candidum. These mould enzymes cause the interior of the cheese to soften and the outside to develop a felt-like layer of white mould. Eventually this white mould produces a secondary growth of yellow mould loaded with the bacteria Brevibacterium linens. Without the use of mould, our beloved Brie would not have its edible downy rind and delectable buttery flavour.

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