Beer is usually made using yeast strains that scientists are familiar with. Common brews like Heineken are created with Saccharomyces strains, which started out as a wild fungus that has been tamed over many generations. The resulting yeast ferments sugar into carbon dioxide and of course, alcohol. Brewers making beer with wild strains of yeast are not sure what they might be working with though, and scientists and brewers wanted to know more about it.
Cody Morris was a brewmaster at Epic Ales when he invited researchers to check out his yeast in action. They toured the brewery, which included casks of so-called 'wild' beer. The investigators zeroed in on one. “We opened it and it was alive,” said Maitreya Dunham, a geneticist at the University of Washington in Seattle who participated in this work. The yeast they saw was hard at work. “It was definitely an actively fermenting mixture,” she noted.
Samples were taken of the brew so that back in the lab, the scientists could learn more about the microbes inside. This was a great opportunity to test a method the team had been developing called Hi-C sequencing. In that technique, a mass of different microbial DNAs can be disentangled because it is treated in a way that causes pieces of DNA with a common origin to crosslink together.
“The inference is that if two pieces of DNA are crosslinking to each other, they must have come from the same cell,” Dunham explained.
With this tool, the team was able to find a totally new kind of yeast, as well as a hybrid of a known strain. The yeasts belong to the genus Pichia, and the hybrid was named Pichia apotheca, Greek for “warehouse” - a nod to its origins in the “Old Warehouse” brew.
These wild strains seem to work with other microbes. The researchers were unable to brew beer with the P. apotheca strain by itself. They also found several other strains in the warehouse beer - Saccharomyces and another yeast genus entirely, Brettanomyces, often found in wild beers.
This work may help scientists understand why microbes spontaneously start fermenting. It also establishes Hi-C as a good way to investigate microbes in beer production.
“This paper provides a proof-of-concept for using this method to study other spontaneously fermented beers,” commented bioengineer Ronn Friedlander, Ph.D., a co-founder of Aeronaut Brewing in Somerville, Massachusetts. He was interested to see that the microbe mix identified by Dunham and colleagues is very similar to a blend sold to brewers as a wild yeast, the “Roeselare” blend by Wyeast. It contains a Belgian-style ale strain, Saccharomyces, Lactobacillus, Pediococcus, and two Brettanomyces strains, Friedlander said.
Friedlander suggested that wild beer fermentation might be more predictable than thought. “This might point to specific niches that must be filled in a microbially stable, aging beer,” he said.
Sources: Science News, Nature