History and Genetics

I have become fascinated by the transition from the production of ales to the production of lager beer in Bavaria in the 15-16th centuries. Many sources suggest that Bavarian brewers were the first to discover that beer could ferment in the cool storage of caves and cellars. It is difficult to say when this cold fermented beer first appeared. In fact, it may be that there is no single point in time at which lager beer appeared. Several sources cite a 1420 Munich Town Council record as mentioning “cold fermented” beer that is assumed to be a predecessor of what we call lager beer today (German Beer Institute, 2006; Jackson, 1999). On the other hand, at least one author suggested that lager beer didn’t emerge until 1500 (Mosher, 2004), yet another suggested that the mid-19th century ushered lager into Munich and Vienna (Noonan, 1996).

So, we do not have unequivocal evidence of a point in time when lager beer emerged. We also do not know the process by which these lager yeasts came into being. Modern genetic investigation and knowledge about the effects of selective pressure on yeast strains by brewers may give us some possible explanations. Recently, some investigators suggested that lager yeasts emerged over a transition period during which yeast hybridized to enable previously thermotolerant yeast (ale yeasts) to become cryrotolerant. Today we dub these cryrotolerant species lager yeast and they are able to ferment in cold temperatures. The distinction between the two types of yeast is somewhat artificial. There is considerable overlap in some yeast species’ ability to tolerate temperatures.

First, a little terminology is in order. While there are hundreds of species of yeasts that have been described in scientific literature, only a few have been specifically linked to the production of quality drinks and breads. Saccharomyces cerevisiae is the most frequently used yeast species in baking and wine-making (although many strains of this species exist). It is also a thermotolerant yeast that is used to produce ales at higher temperatures and is sometimes called a top-fermenting yeast. S. pastorianus (sometimes called S. carlsbergensis) is a cryrotolerant yeast that can ferment at cooler temperatures and is often referred to as a lager or bottom-fermenting yeast.

Early research suggested that the cold-fermenting S. pastorianus was a hybrid of S. cerevisiae and another species, S. bayanus (Martini & Kurtzman, 1985; Rainieri, 2006). S. bayanus has often been used as a synonym for S. uvarum, which is a dubious assumption based on the most modern genetic analysis of the S. uvarum genome (Rainieri, 2006). I won’t get into that controversy here! The view taken by most researchers was that the non-S.Cerevisiae component of S. pastorianus’ genotype was accounted for by the genes contributed by S. Bayanus.

This view, that S. Cerevisiae and S. Bayanus hybridized to produce S. Pastorianus, is questioned by Libkind, et al. (2011) in recent research. They isolated a yeast from Patagonia, S. eubayanus, that is a 99.56% match to the part of the genome of S. pastorianus that is not attributable to S. cerevisiae. Essentially, these authors suggest that today’s major lager yeast is a hybrid of S. cerevisiae, the traditional ale yeast, and a yeast that has never been isolated in Europe, but hails from the New World, namely S. eubayanus.

This poses some temporal problems. If lager beer was being produced in 15th century Europe, it could not have been a S. cerevisiae/S. eubayanus hybrid since a potential carrier of S. eubayanus from the New World would have to pre-date known voyages from South America, which would be well into the 16th century.

Several possibilities may account for this (and this list is not exhaustive).

1. Lager beer as we know it today actually emerged later than the 1420 reference cited above.

2. Some hybrid, yet unidentified, may have produced lager beer in the 15th century.

3. S. eubayanus may have been transported to Europe sometime in the 16th century and hybridized with S. cerevisiae to become the preferred yeast for producing lager beer, making the 1420 date dubious.

4. S. Eubayanus existed in Medieval Europe and hybridized with S. cerevisiae even though the former has never been isolated in the wild in Europe.

What seems reasonable to assume is that at some point in history, a hybridization occurred such that previously thermotolerant yeast evolved into a cryrotolerant species under the selective pressure of brewers who observed and tasted the benefits of cold fermentation. These benefits go beyond merely the fermentation temperatures. Genes in lager yeasts code for different proteins that affect specific metabolic processes of the yeasts and determine which, and at what levels, the yeast can process different types of sugars (but that is an issue for another paper).

Adventures in Yeast – Part II. Do we have a new candidate for the “missing” yeast component?

References

German Beer Institute. (2006). Retrieved from http://www.germanbeerinstitute.com/history.html.

Jackson, M. (1999). The birth of lager. Retrieved from http://www.beerhunter.com/documents/19133-000255.html.

Libkind, D., Hittinger, C. T., Valerio, E., Goncalves, C., Dover, J, Johnston, M., Goncalves, P., & Sampaio, J. P. (2011). Microbe domestication and the identification of the wild genetic stock of lager-brewing yeast. Proceedings of the National Academy of Sciences, 108, 14539-14544.

Martini, A. V., & Kurtzman, C. P. (1985). Deoxyribonucleic acid relatedness among species of the genus Sensu Stricto. International Journal of Systematic Bacteriology. 35, 508-511.

Mosher, R. (2004). Radical brewing. Boulder, CO: Brewers Publications.

Noonan, G. J. (1999). New brewing lager beer. Boulder, CO: Brewers Publications.

Rainieri, S., Kodama, Y., Kaneko, Y., Mikata, K., Nakao, Y., & Ashikari, T. (2006). Pure and Mixed Genetic Lines of bayanus and pastorianus and Their Contribution to the Lager Brewing Strain Genome. Applied and Environmental Microbiology, 72, 3968–3974.

Keg Image courtesy of cbenjasuwan at FreeDigitalPhotos.net