Yeastie Boys trial bacteria-free sour beer

New Zealand brewers Yeastie Boys have become the first beer makers in Britain to produce a sour beer with a new strain of yeast that does not require bacteria to produce lactic acid.

Normally a sour beer gets its sharp taste by lactic acid produced by bacteria – in sour mash, kettle souring or adding bacteria in the fermenter – and alcohol produced by saccharomyces yeast.

This new yeast strain, produced in the US, does both jobs, reducing the pH to create the tart taste of sour beer and producing (low) alcohol through fermentation.

Yeastie Boys creative director, Stu McKinlay, explained: “I picked up on whispers of this amazing yeast, last year, and our head brewer JK was immediately fascinated with the idea of using a brewer’s yeast that removed the traditional need for bacteria to produce a sour ale.

“It took a lot of asking around, a little dumpster diving, and over a year of elapsed time between our first chat and getting Heaven Up into kegs and cans.
“Introducing bacteria to a brewery not only comes with risks but adds fairly significant changes to the brewing and/or fermentation processes”

Head brewer James Kemp added: “This new yeast enables brewers to use standard processes, and gain the complexities of traditional sour fermentation, while lowering usual risks associated with creating sour beer. We expect to see a lot of UK breweries using this yeast in the years ahead.”

The beer made with the new yeast, a 3.8% Berliner Weisse-inspired brew called ‘Heaven Up’, is also out now.

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