This New Yeast Strain Saves Sour Beer Brewers Time, Space And Money

As brewers try to right their balance sheets and pinch pennies in the precarious post business-reopening phase of the coronavirus, they’re seeking new ways to bring economic efficiencies into their craft. A radical new yeast discovery in Philadelphia can help them do that.  

The yeast, colloquially called Philly Sour and now available for commercial and home sale, drastically reduces the time it takes to ferment a beer brewed to taste sour. Sour styles, which remain as popular as ever through the pandemic, can normally take months or years to fully mature as the usual wild yeast strains that lend their sour power slowly work to acidify the beer.  

Philly Sour, on the other hand, can ferment the liquid in ten days total, without the need to follow the traditional method of aging in wooden barrels. Further, the scientist behind the isolation of the strain believes it doesn’t carry the ominous risk of contaminating other parts of the brewery, as do the other known souring yeasts. He recommends following proper sanitation protocols anyway.

“We have screened hundreds of strains with at least 40 different students and I’ve found a handful of fermenting yeasts but this was the unicorn,” says Matt Farber, director of the Brewing Sciences program at the city’s University of the Sciences, whose undergraduate assistant discovered the yeast on a tree while foraging in a West Philadelphia park. “This is the one that does something unique for the industry in terms of changing the way we think about sour beer production.”

After many rounds of brewing trials to ensure their initial results weren’t a fluke, Farber and his students determined the strain does, in fact, produce both lactic acid and ethanol during the primary stage of fermentation. No other known yeast can do that.

“I’m not sure what sure business this yeast had in Philadelphia but we’re going to put it to work,” Farber says.

Several years into the trials, USciences partnered with Canada-based Lallemand Brewing to develop and market the yeast for sale. It’s Lallemand’s first non-saccharomyces (standard brewers yeast) dry yeast.

Lallemand says in a statement, “WildBrew™ Philly Sour … will produce sour beer in 7-10 days at 25°C (77˚F). (Ed note: sour ales typically ferment between 69-72˚.) The acidity produced is described as smooth, elegant, and subtle. The resulting brew is highly balanced with flavor notes of red apple, peach and honeydew melon.”

Some Philadelphia-area breweries who offered to experiment with Philly Sour before it hit the market haven’t concluded their efforts yet but Farber notes from his own lab’s batches, “We’ve liked how saison strains complement the acidity.”

It’s not the first time one of Farber’s discoveries has made news. In 2018, he and a graduate student developed a medium to rapidly test beer for the presence of a disruptive and dangerous diastaticus yeast contamination.