Lager is overwhelmingly the world’s most popular style of beer, accounting for over 90% of all beer consumed. The common misconception regarding lager is that it is a “modern” beer, only made possible by the introduction of technology into brewing in the latter half of the 19th century. In fact, the roots of lager brewing in Bavaria are very much older than that, dating back to the Middle Ages.
“Lager” can be defined as a beer created by cold fermentation with yeast that settles to the bottom of the fermenting vessel, and which undergoes long, cold maturation. The period of maturation gives lager its name in English – the German verb zu lagern means “to store”. Lager is therefore different from ale-type beers which are fermented warm with a yeast that rises to the top of the fermenter, and are not necessarily matured.
Techniques of bottom fermentation and cold maturation were current in Bavaria by the 15th century. The Bavarian climate, with its cold winters and hot summers, created the conditions in which lager brewing could evolve.
The brewing season in Bavaria officially ran from Michaeli (29th September) to Georgi (23rd April) – brewing could not take place during the summer because the beer would spoil. It was therefore necessary to brew sufficient beer by late April to last until late September.
The benefit of lager brewing was that lager was more stable than top fermented beers and would last all through the hot summer, provided it was kept cold. Also, the cold fermented beer had fewer, if any, background flavours, and therefore had a “cleaner” flavour. Cellars, caves and tunnels were constructed to provide summer storage, and ice from lakes and rivers was cut at the end of winter and packed into the beer stores to assist the cooling process.
Around the 15th – 16th century, something extraordinary happened which would eventually change brewing forever – a new yeast strain evolved which allowed beer to be fermented at low temperatures.
In the early Middle Ages, brewers had relied upon wild, airborne, yeast strains to ferment their beer, which typically results in a mixture of top and bottom fermentation. The disadvantage of using wild yeast is the considerable risk of infection from unwanted yeast strains. To avoid this, by the middle of the 14th century, brewers were retaining yeast from one brew and pitching it into the next, rather than relying upon airborne yeasts. Top fermenting yeasts of the Saccharomyces Cerevisiae type were the most common, but bottom fermenting strains were emerging. In 1420, brewers in Munich were given permission to use bottom-fermenting yeasts.
Genetic studies carried out at Stanford University in California have proved that lager yeast was formed several hundred years ago as a hybrid of top fermenting Saccharomyces Cerevisiae and a yeast called Saccharomyces Bayanus. This is remarkable because the genetic structures of the two strains are very different.
The only environment that would have been suitable for such a hybrid yeast to emerge and survive hundreds of years ago would have been a Bavarian brewery, which would have provided malt sugars for the yeast to consume at low temperatures.
Of the hybrid yeast’s two parents, it is the Saccharomyces Bayanus that prefers low temperatures. Over time, cold conditions would have led to the loss of some of the Cerevisiae genes and the retention of the Bayanus genes. This process would have been encouraged by the brewers selecting the portion of the yeast which had settled to the bottom to pitch into their next brew.
An unlikely hybrid, something analogous to a cross between a horse and a pig, had occurred and cold fermentation became possible. By accident, largely because of the extreme Bavarian climate, a huge breakthrough in brewing had taken place which would one day affect the way that nearly all the world’s beer would be brewed.
Lager had been born, somewhere in Bavaria, sometime in the 16th century.
Lager brewing was to remain a largely rural tradition, peculiar to a fairly remote corner of Europe, largely ignored, until the middle of the 19th century, when it was taken up and perfected by some of the greatest brewers that ever lived.