A Sur­prise in the Yeast

A brewing pro­gram in Philadel­phia has come across a wild yeast that not only floc­cu­lates clear but also nat­u­rally pro­duces lac­tic acid. Is GY7B the next big thing for sour beer? By John Holl

Craft Beer & Brewing Magazine - - Contents -

In what could set a new course for quick-sour­ing beer, re­searchers in Philadel­phia have dis­cov­ered a yeast strain that adds lac­tic acid to a beer dur­ing fer­men­ta­tion.

UPON TAST­ING THE BEER for the first time, Matthew J. Far­ber was con­vinced that he had an in­fec­tion in his fer­men­tor. The as­sis­tant pro­fes­sor of bi­ol­ogy and the di­rec­tor of the Brewing Sci­ence pro­gram at Univer­sity of the Sciences in Philadel­phia had made a pi­lot batch of beer on a Sabco sys­tem in the brewing lab us­ing yeast har­vested in the city.

As­sum­ing that, and based on pre­vi­ous ex­pe­ri­ences, the yeast col­lected—if it was up to the task of fer­men­ta­tion—would be wild, the class reg­u­larly uses the Sour Amer­i­can recipe from Michael Ton­s­meire’s book, Amer­i­can Sour Beers. It’s a sim­ple lam­bic-like beer with Ger­man Pil­sner malt, wheat, oats, and a small amount of Wil­lamette hops.

The stu­dents use this recipe be­cause they want to fo­cus on the yeast fla­vor, says Far­ber.

The batch in ques­tion had a clear lac­tic-acid fla­vor, some­thing that was not added in the brewing process and that had not shown up in any of the other pi­lot batches. Fur­ther con­found­ing Far­ber was that the beer was the pale yel­low he was ex­pect­ing but com­pletely clear.

“We spent a lot of time think­ing there was a con­tam­i­na­tion and then spent so much time check­ing for mi­cro­bial con­tam­i­na­tion. When we kept get­ting the same re­sults, by the fourth batch, we re­al­ized that there wasn’t a con­tam­i­na­tion and that the yeast was mak­ing lac­tic acid in fer­men­ta­tion.”

That’s right. There’s a yeast strain that ex­ists that not only fer­ments beer but also pro­duces lac­tic acid. Far­ber, a long-time home­brewer who has stud­ied brewing for years, re­al­ized what a break­through this is—and that there will also be skep­tics. Af­ter he re­al­ized that the lac­tic qual­ity in these batches of beer was com­ing from the yeast, it was tested and vet­ted at ev­ery level. Now, af­ter months of ex­am­i­na­tion, the univer­sity is seek­ing a patent on the ap­pli­ca­tion of the strain and is talking with a some po­ten­tial part­ners—they de- clined to say which ones—in or­der to get the yeast into the hands of home­brew­ers and pro­fes­sional brew­ers alike.

They call it GY7B for now, and it is, in­deed, a novel lac­tic-acid pro­duc­ing yeast ca­pa­ble of acid­i­fy­ing beer to ph 3.5 in as few as five days with fi­nal at­ten­u­a­tion at two to three weeks.

“It’s ready to go,” Far­ber says. “I want to share this with the world.”

A Lucky Find

Founded in 2015, the Univer­sity of Sciences Brewing Sci­ence Cer­tifi­cate pro­gram is de­signed to teach the tech­ni­cal and mi­cro­bi­ol­ogy as­pects be­hind beer. It’s a team-driven teach­ing model with sci­en­tists and brew­ers teach­ing stu­dents both the prac­ti­cal and real-life sce­nar­ios and trends that go into brewing. The pro­gram cul­mi­nates with an in­tern­ship at a brew­ery.

That’s right. There’s a yeast strain that ex­ists that not only fer­ments beer but also pro­duces lac­tic acid. Now, af­ter months of ex­am­i­na­tion, the univer­sity is seek­ing a patent on the ap­pli­ca­tion of the strain and is talking with a some po­ten­tial part­ners—they de­clined to say which ones—to get it into the hands of home­brew­ers and pro­fes­sional brew­ers alike.

Dur­ing the Mi­cro­bi­ol­ogy of Beer course, stu­dents head out into Philadel­phia to find wild-yeast strains ca­pa­ble of fer­men­ta­tion. A re­search as­sis­tant in Far­ber’s lab found GY7B on a back­yard tree in west Philadel­phia. It was col­lected and brought back to the brew­ery’s lab along with other sam­ples col­lected by the stu­dents. Each strain that is vi­able for brewing, says Far­ber, is put through the half-bar­rel fer­men­tor rather than a cool­ship to let the stu­dents and re­searchers “dis­sect what grows.” Char­ac­ter­iz­ing in­di­vid­ual yeast for their fer­men­ta­tion char­ac­ter al­lows a brewer to be more con­sis­tent as op­posed to the spon­ta­neous fer­men­ta­tion in a cool­ship. Pre­vi­ously, as you’d imag­ine, var­i­ous strains of Bret­tanomyces have been har­vested, im­bu­ing the base beer with the tell­tale fla­vors as­so­ci­ated with that wild yeast.

When new yeast sam­ples ar­rive at the Univer­sity’s brew­ery, they are placed in a 10-mil­li­liter tube where they are eval­u­ated for CO2 pro­duc­tion. They’re then stepped up to a half-liter quick-test fer­men­ta­tion. From there, the pro­gram chooses four sam­ples to step up to the next level. As this lacto-pro­duc­ing yeast went through the tests, it “was par­tic­u­larly vig­or­ous and floc­cu­lent” and af­ter brewing and test­ing again was found to be “pleas­antly acidic.”

From there, the mi­cro­bi­ol­o­gists took over, do­ing me­dia plat­ing to try to dis­sect what was hap­pen­ing, and all along they kept brewing it over and over, get­ting the same re­sults. The find­ings and ap­pli­ca­tion in beer were noth­ing short of a ma­jor in­no­va­tion in brewing.

“It gives me goose­bumps,” says Far­ber.

The Taste

“We couldn’t be­lieve it be­cause be­fore this, we didn’t know of any­one brewing with a lac­tic acid–pro­duc­ing yeast,” Far­ber said last fall, stand­ing in the brew­ery while of­fer­ing a sam­ple of the beer.

The beer has a soft wheat char­ac­ter and a rich­ness from the oats. It’s im­pos­si­ble not to no­tice the lac­tic-acid sour snap that is al­most sa­vory lemon, but there are also hints of melon and tart green ap­ple that is more nat­u­ral than an ac­etalde­hyde flaw. The test­ing of the yeast also re­vealed glyc­erol in the mix, which adds sweet­ness and a full body to the oth­er­wise highly at­ten­u­ated beer.

The clar­ity is amaz­ing in the 6 per­cent ABV ale. The beer floc­cu­lates clean, al­most crys­tal clear, giv­ing it the ap­pear­ance that it has been fil­tered and cen­trifuged, some­thing Far­ber says it has not un­der­gone.

“This is a novel spec­i­men mak­ing unique beer.”

When it comes to all this yeast is ca­pa­ble of do­ing, “I wouldn’t be­lieve these things if I didn’t have the data to sup­port it,” Far­ber says.

When the yeast is fi­nally re­leased and gets into brewing sys­tems, it has the op­por­tu­nity to open up new fla­vors in beers and, po­ten­tially, change the way brew­ers ap­proach mak­ing sour ales.

“It’s a faster, more re­pro­ducible yeast, mean­ing sour beer can be made faster and more con­sis­tently, lead­ing to cost sav­ings and mak­ing more sour beer avail­able to drinkers,” says Far­ber.

Left and Be­low » Matthew J. Far­ber (with mash pad­dle and beer glass) brews with a stu­dent of the Brewing Sci­ence Cer­tifi­cate pro­gram.

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