Biochemist finds solution to ‘acid shock’ in craft brewers’ sour beer production

Indiana University researchers have found that conditions common in the production of certain types of craft beer can inhibit the successful production of these beers, jeopardizing a growing segment of an industry whose impact economy was recently estimated at $55 billion.

The conditions, chief among which is high acidity, threaten yeasts typically used in the production of sour beers, one of the fastest growing segments of the craft beer industry. The book, which appears in the journal Food Microbiologyalso reports a method for overcoming the condition, dubbed “terminal acid shock”.

The lead author of the paper is Matthew Bochman, an assistant professor in the Department of Molecular and Cellular Biochemistry at IU Bloomington College of Arts and Sciences and a craft brewing consultant. The research was conducted in conjunction with Upland Brewing Company, a small craft brewery based in Bloomington, Ind.

“This study shows that pre-adaptation of yeast into a readily available, nutritionally dense substance composed of yeast extract, peptides, sugar, and the beer being brewed can ensure proper bottle conditioning of sour beers. “Bochman said. “Simply using untreated dry yeast or rehydrated yeast in water alone should be used with caution in the production of ‘extreme beers’ such as sours.”

The article’s other authors are Caleb Staton and Adam Covey of Upland Brewing; Cody Rogers, graduate student at IU Bloomington; and Devon Veatch, a student at the Ivy Tech Community College of Indiana.

Terminal acid shock occurs when craft brewers add additional yeast to beers after fermentation to create carbonation before bottling, the last step in the traditional brewing process. The problem does not generally affect large commercial breweries that use forced carbonation.

The beer used in the experiment was developed by Upland Brewing, whose previous attempts to brew a variety of sour beer, called “Cauldron”, failed two years in a row due to complications during the bottling phase. , resulting in the loss of 1,600 gallons of beer. Beer. The variety, aged in charred oak barrels filled with Michigan cherries, has a pH of 3, typical acidity for many sour beers.

To conduct the study, Bochman and his colleagues observed the reaction of six strains of brewer’s yeast – or Saccharomyces cerevisiae – exposed to organic acids such as acetic and lactic acid produced by bacteria during brewing. The six strains used in the study are commonly referred to as barrel- and bottle-conditioned brewer’s yeast; California brewer’s yeast; Brewer’s yeast Hefeweizen; Champagne yeast; American ale yeast and pilsner lager yeast. The first and fourth strains were the least affected by pH changes.

“Our analysis revealed that terminal acid shock was not completely lethal to yeast cells, although nearly a third of the yeast died in some experiments,” Bochman said. “The acid, however, significantly inhibited the metabolism of the surviving yeast.”

This slowed metabolism is responsible for the microbes’ inability to “exhale” the carbon dioxide that creates the carbonation during bottling. But the fact that the majority of the yeast survived meant the researchers found they could revive the microorganism by incubation in a nutritionally dense substance typically used in labs called YPD, which contains yeast extract, peptides and sugar.

“Normally breweries just rehydrate dry yeast with water and sugar before bottling, but the acids are too harsh,” Bochman said. “Exposing the yeast to a mixture of YPD and non-carbonated beer a day before bottling boosts the microbes enough to survive in a highly acidic environment.”

The bottling method could become increasingly important as sour beers gain popularity, with the number of varieties exploding in recent years, Bochman said.

“The results of his research have solved a real technical dilemma in the bottle packaging of our sour beers,” said Staton, director of sour operations at Upland Brewing. “As a company, we are committed to sharing information with researchers, as well as the brewing community, as this only drives quality in our industry. We hope this work can be used by other breweries to solve similar problems. “

Additionally, Bochman is the recipient of $13,000 from the Johnson Center for Innovation and Translational Research at IU Bloomington. The one-year grant funded the creation of Wild Pitch Yeast, LLC, a company that helps craft brewers and home brewers extract brewer’s yeast from local sources such as berries, flowers and tree bark , offering the results for resale.

The company has already banked about 300 yeast strains, mostly from Midwestern states such as Indiana, Ohio, Kentucky and Pennsylvania. Bochman has also filed intellectual property disclosures on a number of strains for potential licensing. His partners in the venture are Rob Caputo, executive director of the Brewers of Indiana Guild, and Justin Miller of Black Acre Brewing in Indianapolis.

Comments are closed.