Molds and bacteria for cheese making: not all molds come to harm!

Imagine someone proposing, “I’ll give you 100 euros if you eat this food, but know that it has billions of bacteria and moldin it.” I don’t know about you, but I would hesitate a little and probably turn down the offer! Yet, if the same person offered me a taste of Gorgonzola, the nice creamy kind, well: I would jump at it. Yet, it is the same thing.

Cheeses are the masterpiece of microorganisms. Communities of microbes diverse in nature, shape and size live together and collaborate in transforming milk proteins into an incredible variety of cheeses, each with distinctive flavors and smells.

It must be said that blue cheeses, led in Italy by gorgonzola, do not exactly meet everyone’s taste. I bet that even among you who read the first paragraph of this article there are some who would not flock to gorgonzola, but would definitely stay away from it. In fact, the spicy flavor and very intense smell of this cheese are too strong for some palates. But where do these scents and aromas come from?

Molds and bacteria in blue cheese or blue cheese

Blue-veined cheeses, that is, those streaked with green or blue veins (hence the English name of blue cheese ), are stracchino-type cheeses that are aged for 50 or more days, and have the special feature of harboring molds. They are good, desirable molds because they are responsible for so many biochemical transformations that make cheese tasty and odorous.

One of the most famous molds hosted in blue cheeses is Penicillium roqueforti , which is used precisely in the production of gorgonzola, its French cousin, roquefort, and other cheeses in this category.

The curious thing is that originally these molds came to “contaminate” the cheeses spontaneously, because perhaps they were processed or ripened in caves or other damp places that favored the growth of these microscopic filamentous fungi. Today, however, we no longer leave the colonization of the wheels and the ripening of the cheese to chance, but the molds are selected in a very precise way, checking well that only the desired ones are present, and their spores are inoculated into the milk (before or after coagulation) so as to be sure that they are present in the finished product and that they confer always the same organoleptic characteristics reproducibly.

The forms that are ripening are then pricked with long metal nails. Not for violence, eh, but to allow air to get right to the heart of the molds and thus create a suitable environment for mold growth.

Along with molds, bacteria also grow in blue cheeses. These bacteria degrade almost all of the lactose during the long aging process, thus making the blue meats suitable even for those who are intolerant to this natural sugar.

Molds and bacteria in flowered rind cheeses

Other molds of dairy interest are found on a second type of products, so-called “bloomy rind” cheeses. These cheeses, such as Brie and Camembert, are covered with a white mold rind, Penicillium camemberti, which is safe for eating (in fact, the rind of Brie can be eaten).

These molds are added to the milk before coagulation or sprinkled over the molds, which are then left to ripen for several weeks. Again, bacteria play an essential role in creating thearoma and texture of the cheese, in cooperation with molds.

Among the bacteria that can grow in these cheeses, such as Camembert, is Brevibacterium linens, which is also present on our skin and is responsible for producing strongly odorous molecules.

Who knows why, in our minds, these odorous substances are perceived differently if they come from an inviting cheese or from a person’s feet? We are such weirdos!

Mold on the rind of Taleggio cheese: a photograph

In conclusion of this article, could I leave you without a photograph taken under a microscope? Of course not! I wanted to take a look at the mold I found on the rind of Taleggio, one of my favorite cheeses.

Mold on the rind of taleggio cheese
Mold on the rind of taleggio cheese. 400× magnification, methylene blue staining.

In the process of making taleggio cheese , molds are not voluntarily inoculated into the mold, but grow spontaneously on its surface. The most common genera are Penicillium, Mucor, and Geotrichum. Their presence on or in the cheese paste is accepted because they are nontoxic molds, and their quantity is monitored so as to always ensure quality products.

Conclusion: yay for mold!

Thus, we have seen that not all molds are bad, not all are to be associated with inedible foods and, therefore, to be avoided. Some, indeed, are our valuable allies in the production of typical products such as blue-veined and flowered rind cheeses, true masterpieces protected by certifications guaranteeing their origin and quality, and which the rest of the world envies us.

Sources:

Lecocq J. and Gueguen M., Effects of pH and Sodium Chloride on the Interactions Between Geotrichum candidum and Brevibacterium linens, Journal of Dairy Science, 1994, 77 (10), 2890-2899, DOI:10.3168/jds.S0022-0302(94)77229-5.

Deetae P. et al, Production of volatile aroma compounds by bacterial strains isolated from different surface-ripened French cheeses, Appl. Microbiol. Biotechnol., 2007, 76 (5), 1161-71, DOI:10.1007/s00253-007-1095-5

Cantor, M. D. et al, Blue cheese. Cheese: Chemistry, Physics and Microbiology, 2004, 175-198, DOI:10.1016/S1874-558X(04)80044-7

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