Legend says that blue cheese was discovered in Roquefort, France, when a young man snacking on bread and cheese made from ewe’s milk saw a beautiful woman in the distance. He promptly left his meal in a relatively cool cave to approach her. When he returned to his leftovers many months later, he found the first Roquefort blue cheese.
A new study sheds light on the origin story of blue cheese by investigating the genetic history of the blue cheese mold: Penicillium roqueforti. The fungal spores of P. roqueforti create the eponymous blue veins. Researchers in France used genetic data they collected from cheese strains from different environments all around the world. In addition, they performed tests of growth and spore formation of various strains Using both datasets, the researchers reconstructed the various changes blue cheese mold has undergone in the past.
The Roquefort population of blue cheese mold has kept its genetic diversity, likely due to mild selection pressures during the pre-industrial time. Roquefort blue cheese mold grows slower in cheese, compared to industrial strains, and has weaker lipolytic activity. This slow maturation reflects how cheese in this region is made—lack of refrigeration and the use of ewe’s milk, which is only produced between February and July. These strains have weaker lipolytic activity, which means the cheese does not become over-degraded during this time. Lipolytic activity also influences texture. Volatile compounds generated from lipolytic activity creates a signature flavor and pungency. In fact, Roquefort and non-Roquefort blue cheese mold populations have different volatile compound signatures and, therefore, slightly different taste and flavor.
Genetic diversity has been lost in the yeast that make blue cheese. Industrialization of cheese production has created strong selection for cheeses that create mature blue cheese quickly. This mirrors what we have seen in crop and livestock production. Lost genetic diversity reduces our ability to respond to changing conditions and adapt our food production accordingly. Though the cheese-making industry keep multiple strains for either mild or strong blue cheese, genetic diversity is still heavily reduced, or bottlenecked, compared to pre-industrial times.
And back to that legend—how did blue cheese originate? Actually, not from accidental contamination from moldy bread in a caves. First, old French texts suggest that blue cheese molds colonized cheese from within and not on the surface. Genetically, blue cheese molds do not come from food-spoiling molds. Moreover, surveys of caves have failed to find P. roqueforti spores. Nor can researchers cultivaate them from cheese cellars. This leaves one option: blue cheese mold probably came from a plant pathogen of rye, which made its way into the flour and then the baked bread. This idea is also supported by other Penicillium species that tend to infect or decompose plants.
Blue cheese mold provides an excellent example of rapid adaptation and potentially a model for researchers to use when exploring domestication in microbes.