Study: Why green Bayley Hazen Blue cheese turned white

The second was the scraping of samples from the rinds of 50 blue cheese wheels. The importance of those samples, though, wouldn’t become clear for many years.

Researchers have used the proposal-day material as a time capsule to prove that a mold species in the cheese cave rapidly evolved, transforming a signature cheese before its makers’ eyes.

The cheese, called Bayley Hazen Blue, is aged in underground vaults for three to four months while wild microbes from the air colonize its rind. The end product used to be mottled with vivid green. Over a couple of years, those cheeses changed from green to white. Lab experiments showed that a mold species in the cave had mutated, losing its ability to make pigment — like cave-dwelling animals that evolve in the dark to be albino.

The results were published last month in the journal Current Biology.

“There’s a lot of luck in this,” said Benjamin Wolfe, a microbiome scientist at Tufts University. His lab studies cheese from Jasper Hill Farm in Greensboro, Vermont, along with other aged and fermented foods.

His former adviser, Rachel Dutton, had been in Greensboro years earlier for her own lab’s research when she happened to meet Charlie Kalish, a farm intern at the time. In 2016, Kalish wanted to propose to Dutton at the farm where they’d met. He enlisted help from Wolfe.

“I was part of a scheme,” Wolfe said. “I told her, let’s go sample Bayley Hazen Blue!”

First she said yes to Wolfe about the trip to Vermont. Then she said yes to Kalish in the cheese cave. (They were married later that year.)

The cheese wheels in the cave that day had their usual distinctive rinds: a “very avocado-limey-green color,” Wolfe said. But not long after, they began to fade.

“It was subtle at first but became obvious over a period of months,” said Mateo Kehler, who founded Jasper Hill Farm with his brother Andy. By 2022, the Bayley Hazen Blue wheels that the cheesemakers had put into their vaults just months earlier emerged not green, but snow-white.

The cheesemakers weren’t mad about it. White cheese is potentially an easier sell to consumers than a bright green one. They were curious, though.

“Evolution in action”

The color change might have meant that a new microbe was dominating the cheese rind ecosystem. Continuing research at Tufts, though, hinted at a different explanation. The scientists knew the green color came from a mold called Penicillium solitum. In the lab, they’d noticed that mold grown from the farm sometimes spontaneously switched from green to white. The reason was a mutation in a gene that makes melanin.

The scientists wondered whether a similar change had happened to the wild P. solitum population in the cheese cave. Then Wolfe remembered his rind samples from 2016, which were still sitting in a lab freezer.

By collecting new samples in 2022 and comparing their genetics with those of the older samples, the researchers saw that mutant P. solitum strains had taken over. And the mutants lacked the ability to make melanin.

“Melanin is pretty costly,” Wolfe said. An organism that lives in the dark and doesn’t need to protect its cells from the sun can save energy by not manufacturing this molecule. Many cave-dwelling animals — including fishes, salamanders and worms — have also lost their melanin-making ability over time and have evolved to be colorless.

This is a “perfect example of evolution in action,” said Sam O’Donnell, a fungal genomicist at the University of Wisconsin at Madison who wasn’t involved in the research.

A similar kind of evolution seems to have happened under the eye of historical cheesemakers. Brie and Camembert cheeses both get their furry white rind from the French mold Penicillium camemberti. But that mold’s wild ancestor was bluish-green.

Wolfe considers these changes “unintentional domestication.” Not unlike domestic chickens or dairy cows, cheesemaking molds look different from their wild ancestors because of humans and our tastes.

Now Wolfe is helping the Vermont cheesemakers to test whether their discovery can lead to new cheeses.

They started with two of the farm’s signature cheeses, which — unlike Bayley Hazen Blue, colonized by free-floating cave microbes — are usually made by deliberately adding the traditional P. camemberti. This time, the cheesemakers instead used the mutant white P. solitum mold.

The initial trials are “very promising,” Kehler said. “Rinds are snow-white, delicate and thin. Flavor is mushroomy.

“I think we are onto something special,” he said.