Beer as we know it wouldn’t be possible without yeast. In addition to converting sugars into ethanol and carbon dioxide (providing the booze and the bubbles), different brewing yeast strains can contribute all sorts of different flavor and aroma characteristics to the final product. Hop and malt additions may receive top billing on the average craft beer label, but one sip of a clove-and-banana-laden German-style hefeweizen or a peppery Belgian saison should be sufficient proof of yeast’s ability to carry the team when called upon. Many U.S. brewers do favor relatively neutral yeast strains, but, even without directly contributing significant flavors or aromas, the choice of a yeast strain will still ultimately affect how those other ingredients in the beer are perceived.
The inherent difficulties of managing these colonies of single-celled organisms has influenced the course of brewing history, and today our understanding of these for-hire enzymatic pouches remains a bit patchy. We can’t easily observe them at work. They frequently arrive to us in ways as ill-befitting of their importance as dehydrated packages that look like they might just as easily contain a teabag. Even Germany’s Reinheitsgebot Purity Law initially gave them the shaft (yeast wasn’t scientifically understood for another few hundred years). Yet brewing yeasts still manage to reassert their quiet presence—as well as remind us they’re never entirely under our control.
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Yeast are miniscule, generally unicellular fungi. They exist to create more yeast, to find sugars and other nutrients to sustain themselves long enough to procreate, and along the way they just so happen to transform mixtures of sugar, hops, and water into something more special than their constituent parts. They usually procreate by a budding process, via which they create genetically identical copies of themselves that grow to the same size as the original within a matter of hours.
They do not, as far as we know, dream of greatness.
Yeast’s role in the fermentation of beer didn’t become well established until the late 1800s, when Louis Pasteur published his Études sur la Bière (Studies on Beer) and Emil Hansen managed to isolate an example of bottom-fermenting yeast at Carlsberg Laboratory in Copenhagen. Up until then, although brewers knew that harvesting the rich foam from a fermenting batch of beer could be used to initiate the next ferment (without the need for divine intervention or breaking out the old brewing sticks), the technological capabilities up until then hadn’t progressed sufficiently far for them to be able to do all that much about it. The international scientific community gradually honed the skills needed to isolate, identify, and transport yeast strains safely, and the organisms responsible for the magical parts of the brewing process were finally becoming understood.
In Amber, Gold & Black, beer historian Martyn Cornell carefully details what happened shortly afterwards. In 1897, the British chemist Horace Brown told a European audience of findings in America that had yielded the ability to package bottled beer that, unlike its bottle-conditioned predecessors, “would remain ‘bright’ in the bottle. It did not take long for the technology to cross the Atlantic.” Breweries were soon marketing these new and improved “sparkling” ales (which were artificially carbonated, instead of naturally carbonated by being bottled with yeast), thereby saving thirsty consumers from yeast’s unseemly appearance. Innovations for removing yeast and improving the stability of the final product would eventually involve all sorts of things, including centrifugal filtration, pasteurization, and fining agents like isinglass, gelatin, and Irish moss.
Yeast was unavailable for comment on these developments.