The origins of Lager yeast - a theory

Schlenkerla Smoke Kiln

century old lagering rock cellars underneath Schlenkerla brewery

The dominating beer style, at least by volume, in the world today is lager beer. This term derives from the fact, that in the classic hand craft version it needs to ferment and lager for weeks or even months to fully develop its aroma and flavor (industrial breweries have developed various techniques in the last decades to shorten the largering time, but as this theory here is a historical approach to the topic these very new technologies shall not be taken into account). By comparison most ales will reach their final rate of fermentation in only a few days. The main reason for this different behaviour is the temperature at which the fermentation and lagering takes place. Lager beer yeast, i.e. bottom fermenting yeast, typically ferments best at temperatures around 8°C, whereas ale yeast, i.e. top fermenting yeast, usually needs 15°C and more. And as with many chemical processes, fermentation is quicker at higher temperatures.

Lager beer became dominant at the end of the 19th century with the invention of artifical cooling, which enabled brewers to produce this style independently of outside conditions. In Germany these are mostly Pilsener style beers, which are similar to (but not identical) to Pilsener beers coming from the city of Pilsen in Bohemia, Czech Republic. (Note: The term "Lager" in English is used in a much broader meaning than in German. The former is basically any bottom fermented and lagered beer, the latter is usually a relatively mild hopped full beer of 11-12% original gravity as it is common in southern Germany; Germans do not name Pilsener a Lager beer.)

In some publications one can read, that the very existence of Lager yeast is based on the cooling technology invention, but that is a myth. Before artifical cooling it was common to brew bottom fermenting lagers in the winter and top fermenting ales in the summer. Only brewers who had access to natural cool storage, e.g. rock cellars, where able to brew lager style in the summer, too. And these lagers were often favoured over ales, as they were considered to be better digestable (even some modern studies suggest that ale yeast  produces more esthers and hence increases the risk of headaches for the drinker). This favourism can be seen in old court records from the city of Nuremberg dating back to the 14th century, in which brewers without rock cellars sued other brewers with rock cellars for illegally selling "cold" (i.e. bottom fermented) beer in the summer (there was a city law against this pratice to prevent competition between breweries). These historic rock cellars - like the one at Schlenkerla dating back to 14th century and still in use today (see image) - usually have temperatures between 7° and 10° C.

Another legend found in many texts around beer is, that brewers in the past did not know yeast and that all beer was fermented spontaneously. This might have been the case around the time of invention of beer some 10.000 years ago. But with the arrival of monastery-breweries and hence a scientific and hand-craft approach to brewing in the 8th century A.D. spontaneous fermentation became uncommon apart from a few exceptions like Lambic beers. At the latest then brewers very well knew what yeast was, and what they needed it for. Some people also claim that yeast was unknown since it was not mentioned in the famed Bavarian Beer Purity Law of 1516 as an allowed ingredient, but there is another explanation for that: An ingredient is used up in the production process, whereas yeast as natural organism thrives on beer, i.e. at the end of fermentation there will be more yeast than at the beginning, and from that point of view it is not an ingredient. Sounds all very theoretical and speculation? No! There is proof for the assessment (see comment on the 22nd November 1500) that yeast was well known: There are court records from the city of Munich from 15th century, in which brewers and bakers fought over who had the yeast monopoly, i.e. who had the (financially attractive) right to supply the other party.

In fact, yeast was so important, that there was an own profession to handle it: The Hefner (or Häfner, German for "yeaster". It is pronounced like the well known name Hugh Hefner, the founder of Playboy, and yes: he is of German ancestry and therefore probably came from a family of yeast handling craft men). Hefner remains a common name in Franconia today. The Hefner's job was to harvest the yeast at the end of fermentation and prepare it for the next batch. The left over beer in the yeast was pressed out and sold as affordable beer to poor people.

Yeast is a living organism, and according to the theory of evolution by Charles Darwin,  the fittest (i.e. the best environmentally adapted) organism will survive. And so the pieces fall into place: The natural temperature in (Franconian) rock cellars is around 8°C. The first batch of beer started with a mix of yeast strains and the strain that coped best with rock cellar environment (i.e. 8°C) multiplied the most. The yeaster harvested this yeast mix at the end of fermentation, and added it to the next batch of beer. The well adapted yeast had a head start (since it was larger by proportion already due to the stronger growth in the first batch) and hence outgrew the competing yeast strains even further. This process happened in each batch over and over again, for months, years, decades and even for centuries. In effect, it is a breeding program for yeast strains working best at 8°C. So quite possibly Franconian breweries were breeding Lager yeasts at least for the last 600 years, and since Franconia and Bohemia (today Czech republic) are neighbouring areas and culturally very similar, it can be assumed that Bohemians did the same. Both the Franconian Lager (which Schlenkerla Smoked Beer is a special version of) and Czech Pilsener are representatives of these old beer styles. With the invention of artifical cooling this fermenting technique became available everywhere and anytime, and so Lagers and Pilseners left their "birth ground" with their yeast and conquered the brewing world.

One last interesting fact: The ammonia ice machine was invented by Franconia-born Carl von Linde in the 1870s and supported by many breweries. So one could argue that without Franconia and breweries, there would be no fridges in the world today. You're welcome!

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