Yeast have us trained – we cook their food for them, and seat them right at the table for the feast. Bellies full, a few belches, belts undone and pants unbuttoned, the yeast will lie down for a nap at the bottom of the fermenter; they get a ride to the party, eat/drink, then sleep – repeat. Not a bad life at all.

Yeast, though, is a capricious creature. Slight variations in temperature, pressure, quantity, among other things, are enough for them to provide a different flavoured beer. The yeast and bacteria that ferment our beers are found floating through the air everywhere; the beer and wine, the yoghurt and bread, the pickles and sauerkraut (except for some of the store-bought stuff). Yeast ferments the sugars into the alcohol that makes beer fun (in appropriate amounts), it makes many little flavour and aroma compounds that makes beer more interesting (if done well), and it makes the carbon-dioxide that helps us to taste those nuanced flavours; in other words, yeast makes beer. Despite its key role in beer, our understanding of the history of yeast is either unknown to us, or largely misunderstood.

One common myth is that all beer before Louis Pasteur was sour, or spontaneously fermented. This has been proven false by many documents and historians, who have shown that medieval authors wrote that beer was either bitter or sweet, and would only become sour if it had spoiled. Some Belgian lambic (a type of spontaneously fermented beer, usually tart and sour) breweries maintain that historically people had more of a taste for sour than our current selves, now that sugar is cheap and widely available. This is possible, however it should be noted that multiple historical sources recognise a discontent for soured beer. Could it have been a regional taste? Sugar was still a luxury item until the 18th century, while according to historian Roel Mulder, lambic seems to have its origins at around the same time or even a little later, in the 18th or early 19th century.

Though it should be noted that the first of beers were most certainly spontaneously fermented, there is enough evidence from ancient Egypt and the medieval times to show that humans not only knew about yeast, but, in fact, had people responsible for yeast: 1st century CE, Greco-Egyptian papri denote a profession known as zymonrgos, or “yeast-maker”; in medieval Bavaria the professional was known as a hefener. This demonstrates that the yeast was bred, cultivated and artificially added, beer was not spontaneously fermented. Certainly artificially inoculated beer can still sour, but adding yeast makes sure the wort will begin fermentation quickly, the yeast outcompete bacteria and produce alcohol, which is bactericidal. This would allow us some time to drink it before much of the bacteria (and thus, sourness) developed further.

From this we know that people learned early on how to transfer yeast from one batch to another. Transferring would have been done by scooping foam from the still-fermenting top of the vessel, dumping new wort onto the old yeast, or by gathering the yeast with a linen or wooden tool and drying it. This process selected for the better brewing yeasts, in a way a non-scientific genetic modification through natural selection. In the days of yore, English brewers called the foam atop the fermenting liquid “godisgood”, when one saw this foam, they knew that the beer was beginning a good, strong fermentation. The yeast that dominates this fermentation was deemed a living organism and named in 1837, then given its biological label in 1838: Saccharomyces,or sugar fungus. Though this argument was not without its controversy. Mere decades later Louis Pasteur would go on to prove this in his seminal work Études sur la Bière. This work detailed the biological nature of yeast, as well as concluding that bacterial infection is the source of a beer’s “sickness”.

The industrial revolution gave way to many new advances in technology, many of which breweries made use of. Lager beer had been produced for centuries in Bavaria and Bohemia, but in the mid-to-late 1800’s and early 1900’s lager beer, specifically of the pale variety (thanks Pilsner Urquell!), was spreading so rapidly that it was obliterating many breweries and beer styles in its wake. Up in the Carlsberg brewery, in Copenhagen, a man named Emil Christian Hansen worked to isolate individual yeast strains from the variety that was normally added to beer. In the late 1800’s he had separated pure cells of yeast, then researching which produced the best lager. In 1908 he had selected the strain which he found was best suited for production. Having singled this out, Hansen had created a pure culture of yeast for brewing that would overtake the brewing world. A century later we would learn that there was likely more than one distinct, independent evolution of lager yeast, one of which is Bohemian. To this day it is unsure who began using lager yeast first, whilst many sources report Bavaria, some historians have more recently claimed to find documents stating that lager brewing was taken from Bohemia to the neighbouring Bavaria; maybe it was both concurrently, we don’t know, but what matters most is that it happened. Lager’s world domination was in part due to colour, in part due to timing and place, and in part due to the scientific advancements in the field of brewing, all of which combined to create something beautiful looking, clean tasting and longer lasting.

Nowadays most beer is made from pure culture yeast purchased from a lab, however, recently wild fermented beers and lambics have seen a revival. Non-commercial yeast adds a special terroir to the beer, something connected to the land, air and region in which it’s brewed. This is what historically helped to create so much of the diversity in our beers today, and the taste of multicultural beer can again be found throughout the world, offering a unique experience and, hopefully, a real pleasure.

Yeast has always been somewhat magical. The “other” famous Michael Jackson notes the relation between the Dutch word gist (pronounced “with a swallowed ‘g’, meaning ‘yeast’) and the English word “yeast”; gist also bears a striking resemblance to the German word geist, which can translate to “spirit”, these words are, in fact, related. The word spirit is also used in relation to alcohols. Yeast has always played that magical role in beer, without it we’d lose much more than just the alcohol, we’d also lose the flavour and health benefits of fermentation. It’s believed that humans developed a love for this taste from wild fermenting fruit, and that this love even went on to help drive us to the agricultural revolution, about 10,000 years ago. It’s been a long journey since then and much has changed, but yeast continues  to create a magical drink for us to taste and share – that much has stayed the same and certainly will for many years to come.