PHILADELPHIA — A yeast scraped off the bark of a dogwood tree in a Philadelphia cemetery is winning accolades in the beer industry – both for the sour flavor it produces and the time it saves in the brew house.
Captured in West Philadelphia's Woodland Cemetery and isolated in the brewing sciences lab at the University of the Sciences in West Philadelphia, the yeast produces both alcohol and the lactic acid needed for the types of sour beers, such as kettle sours, that are becoming ever more popular with drinkers.
Making sour beer typically requires a short delay in the brewing kettle with an inoculation of bacteria or a long delay in the wooden barrels associated with Belgian-style sour ales. Philly Sour yeast, the brand name for the yeast found in Philadelphia and now sold worldwide by Lallemand Inc., produces sour beers without the extra step.
"We can skip that whole kettle sour process, so it's saving us a full 24-plus hours of time in our kettle when we otherwise would be stuck just not being able to brew beer," said Joel Sprick, quality manager at Levante Brewing in West Chester. "That time savings alone has been really, really beneficial to us."
Since Lallemand started selling Philly Sour last year, the yeast, now coming from a facility in Denmark, has been welcomed widely, based on the Instagram hashtag #phillysour, which shows posts from all over the United States, across Europe in England, Sweden and Russia, and even as far away as South Korea.
Beers made with the yeast are winning praise. An editor at Beer and Brewing, a trade publication, made a wheat beer that he described as "softly tart, not sharply so" and "simple but delightful." A Delaware County reviewer of Pushing Up Petals Philly Sour from Punch Buggy Brewing in Kensington said the beer had "a nice raspberry pucker."
Tired Hands Brewing Co. in Ardmore and Free Will Brewing Co. in Perkasie are also among the Philadelphia-area breweries that have used Philly Sour and were happy with the results.
Philly Sour – and the increasingly popular Norwegian yeasts called kveik – are bringing wider attention to yeast, beer's mostly unsung heroes. For years most of the news out of the $29 billion craft brewing world has been about hops and the race to load beer with more and newer varieties of the flower buds that give beer its bitterness but also enticing herbal, citrusy and piney flavors.
"I don't know if the enthusiasm for hops will ever really wane, but with so many beer options available, there is definitely the space for some breweries to focus more on other ingredients," said Gerard Olson, owner of Forest & Main Brewing Co. in Ambler, which every spring forages for yeast from flowers on the property and uses them for that season's saisons.
Matt Farber, the University of the Sciences professor who isolated the Philly Sour yeast after one of his students found it more than five years ago, by contrast, described his approach to the cultivation of yeast as "ivory tower."
The process starts with Farber sending students out into the neighborhood with Ziploc bags to collect samples, leavings, scrapings from bark and other materials that might have yeast on them. Those materials are tested for fermentation.
If they do ferment, the next step is isolating individual types of yeast in petri dishes. "That's how we can get something like Philly Sour to market," Farber said. It also helps ensure safety from what Farber called "opportunistic pathogens" that can be found in some mixed cultures and yeast strains that can harm people with weakened immune systems, he said.
After a few rounds of brewing in the laboratory with the yeast off the dogwood tree, Farber was convinced that they had something special and potentially valuable commercially.
Kurt Grunwald, an alumnus of Farber's brewing science certificate program and now quality manager at Tired Hands, recalled tasting one of the trial batches in 2017 when he was a student there and finding it hard to believe that the beer had not been soured in a wooden barrel.
Because the university owns any intellectual property that comes out of his lab, Farber had to report it. "The university decided to move forward with commercialization," he said.
Part of the licensing strategy involved the application for a patent, not on the yeast itself, but on the process of making sour beer with the yeast from Woodland Cemetery. To get that patent, the university and Farber will likely have to prove that Philly Sour is a new yeast species.
But some experts say Philly Sour is a strain of Lachancea thermotolerans. That type of yeast has been commercially available for years, according to Chuck Skypeck, technical brewing projects manager at the Brewers' Association, a trade group for small and independent breweries.
Bryan Heit, a home brewer and microbiologist at Western University in Ontario who blogs at Sui Generis Brewing, said his analysis of the information submitted for a provisional patent shows that Philly Sour is not a new species of yeast.
"I'm not a fan of the patent, but I really like the yeast. It's got a nice flavor profile," Heit said on an episode of the Milk the Funk podcast last month.
Molly Browning, East Coast technical sales manager for Lallemand, acknowledged that other souring beer yeasts have been on the market. "We've been able to promote it globally as something that's really unique," Browning said.
Among the competitors are yeasts from Lachancea LLC, which in 2016 licensed its first strain of lactic-acid-producing yeast, according to company cofounder John Sheppard, a professor of bioprocessing science at North Carolina State University.
Farber said Philly Sour "differs in critical DNA sequences" and in other ways that "collectively provide evidence for a unique" species. Further, he said, none of the other lactic-acid producing yeasts on the market "produce the same sour beer flavor or fermentation performance."
Philly Sour might not be one and done for Farber. The scientist said he has other promising yeast strains in his lab but nothing he's ready to talk about and nothing as exciting as Philly Sour.
"Philly Sour was the unicorn. It was that serendipitous discovery that, honestly, fell into our laps," he said.