The evolutionary story behind soft cheese

White and downy on the outside, creamy and supple on the inside, bloomy-rind cheeses such as Camembert and Brie dominate fromageries the world over. You may not know Penicillium camemberti by name, but you've likely tasted the fruits of its labours. The mould species plays a vital role in both the character and creation of some of the most quintessential French cheeses. Given its cultural and economic importance, surprisingly little was known about its evolution, say scientists from the French National Centre for Scientific Research (CNRS) in Paris.

Similar to the way in which people turned gentler, more docile wolves into man's best friend, bloomyrind cheeses are the result of human selection, the researchers found. From the Middle Ages to the mid20th century, Brie was blue. The journey of cool-toned, bloomy-rind cheeses to the unpigmented icons omnipresent in refrigerated display cases today is likewise the result of a domestication process.

“Penicillium camemberti is the result of a strong bottleneck in the sense that there was a selection of one white mutant, which is now replicated clonally,” says CNRS research scientist Jeanne Ropars, lead author of the study recently published in the journal Current Biology.

At the start of the 20th century, consumers started showing a preference for white rinds over grey-green, and the strain behind the former — P. camemberti — has been cultured ever since. While the cheesemakers of the past weren't aware of the science behind the choices they were making, explains Ropars, they domesticated microorganisms intuitively by selecting particular traits such as colour, growth and production of mycotoxins.

“Back in the day, when they were making cheeses without knowing something was actually growing on them, whenever they had a cheese that was OK for people to eat, they would preserve a piece of that cheese and they would use it as the inoculum (culture) for the next year's cheeses,” adds Ricardo C. Rodríguez de la Vega, an evolutionary biologist at CNRS and study author.

Rich in nutrients, cheese is an exemplary medium for things to grow, he says. And because of their rapid rate of growth, fungi make perfect subjects for studying adaptation. “These organisms are easy to study in a sense because they are small — genomes are small — and they grow very fast. So it makes a fantastic model to study rapid adaptation, in this case to human-generated conditions,” explains Rodríguez de la Vega.

Ropars adds: “Our question was to understand how organisms adapt to new environments — how they can cope with the change in their environment — and cheese was ideal to do that.”

Through their research, they identified the diversification of P. camemberti into two varieties. Using genomic analysis and laboratory experiments, they found that domestication took place in several stages over many generations. The first domestication event resulted in P. biforme — a grey-green, cheese-specific relative, which is often used to make fresh goat's cheese today. Followed by a more recent one, which gave rise to the two varieties: the white and fluffy P. camemberti var. “camemberti,” and the flat and greyish var. “caseifulvum.”

The existence of these two forms of P. camemberti was one of the greatest surprises of their study, explains Rodríguez de la Vega. “Even if they are 99.9999 per cent identical, the two varieties display very different phenotypes in terms of their cheesemaking attributes.”

By shedding light on these “closely related but different lineages,” each bringing its own advantages to cheesemaking, the researchers say they hope to encourage further research into other traits. The study also raises questions, they add, by highlighting the limited number of cheesemaking strains used globally.

While in the past, cheesemakers used local cultures — carried forward in earthenware vessels, wooden cheesemaking tools or past successful batches — today, most buy them from companies known as culture houses. Freeze-dried and sold widely, producers as far apart as Canada and Australia could conceivably be spraying the same strain of P. camemberti on their curds. “Roughly 80 per cent of culture houses' products are quite similar,” David Gibbons writes in The Oxford Companion to Cheese, “without great differentiation from one company to the next.”

This homogeneity is an issue, says Ropars. “Cheese producers are only using one strain and the genetic diversity is degenerating … For them, it would be very interesting to recoup some genetic diversity in P. camemberti to keep the strain alive. Because the only (outcome) is the death of your strain.”

Producers sometimes need to go back to their stock strains when they encounter issues with factors such as growth or the quality of the end product, explains Rodríguez de la Vega.

While cheesemakers initially turned to freeze-dried packets of cultures as a way to achieve more consistency in flavour and texture, this standardization has resulted in less variety.

“In this industrialization, we have lost diversity. And the only way to recover would be to reincorporate genetic diversity into the game. And the only way we have to reincorporate genetic diversity into the game is to clone these strains with something they are more closely related (to),” says Rodríguez de la Vega.

“Having identified P. biforme as the extant, diverse population from which the original P. camemberti was domesticated, we should be able to (recover) genetic diversity.”