Yeast hunting at historic Caucasus mountain brewing sites: Investigations for special brewing yeasts in Georgia

Mathias Hutzler (Technische Universität München, Germany), Lia Amiranashvili (Georgian Technical University, Georgia), Juan Eizaguirre (Universidad Nacional del Comahue, Argentina), Giorgi Kvartskhava (Georgian Technical University, Georgia) and Martin Zarnkow (Technische Universität München, Germany)

The most successful beer in the world is lager, which is fermented at low temperatures. The lager beer marketed in Bavaria has been scientifically brought up to world level at the Technical University of Munich (TUM), among others. The basic raw materials need for producing this kind of lager are the same as for most beers: barley and hops. However, the key to the success of lager is the cold-tolerant yeast known as ‘bottom-fermenting yeast’ (due to the fact that it that settles on the bottom of the fermentation vessel bottom after fermentation). This yeast is a hybrid whose exact "parents" have not been found yet.

For several years, brewing and beverage experts Mathias Hutzler and Martin Zarnkow have been linking the field of yeast hunting (generating novel yeast strains from the environment, indigenous fermentations, brewery raw materials and the brewing environment) with historical contexts. Mathias Hutzler focuses on the isolation and characterisation of the brewing potential of yeasts and Martin Zarnkow focuses on historical brewing processes and the linking of the scientific data with archaeological and anthropological facts. Together they are working on the newly created thematic complex of ‘Archeo-Fermentation’ at the Weihenstephan Research Centre for Brewing and Food Quality at the Technical University of Munich, Germany (Bellut et al., 2018, Hutzler, 2021, Hutzler et al., 2019, Meussdoerffer and Zarnkow, 2016, Michel et al., 2016, Bellut et al., 2019, Methner et al., 2022a, Methner et al., 2022b, Pieczonka et al., 2022, Hutzler, 2022, Hutzler et al., 2021, Dietrich et al., 2020). So, in 2016, they decided to turn this body of accrued knowledge to tackle the questions of the origins of the key to the world’s most successful beer. From their research, they know that hops came to Central Europe from Georgia and that many other fruits also originated from this country, the authors had a hunch that the potential place of origin for the ancestors of bottom-fermenting yeast might also be in Georgia.

For their investigations, they put together a team of experts, including local scientists and experts Giorgi Kvartskhava (wine and fermentation expert and chemist), Lia Amiranashvili (wine and fermentation expert and microbiologist) and Juan Eizaguirre (biotechnologist and expert on cryotolerant yeasts and their isolation). In addition, the TUM team (Mathias Hutzler and Martin Zarnkow) and the Argentinian yeast scientist, Juan Ignacio Eizaguirre (Universidad Nacional del Comahue, Bariloche), contacted Lia Amiranashvili and Giorgi Kvartskhava from the Georgian Technical University (GTU) in Tbilisi, Georgia. See Figure 1. The researchers planned their expedition so that they could cover different sites in Georgia (especially in its isolated high mountain areas) in order to analyse the microbial biodiversity of the region and to also conduct anthropological studies on brewing in the high mountain region of the Caucasus.

Figure 1: On a ‘yeast hunt’ in the High Caucasus. Researchers Martin Zarnkow, Juan Eizaguirre, Giorgi Kvartskhava and Mathias Hutzler (from left to right) in Akhieli, a community in the Khevsureti region, Georgia. Photo courtesy of Juan Ignacio Eizaguirre.

Lush forests with great biodiversity

Yeasts occur everywhere in nature; there are more than 1,600 known species, each with different properties. The biological diversity of the environment is also reflected in the biodiversity of yeasts and, thus, in the diversity of yeast-fermented foods and beverages. The scientific team hypothesizes that the fermenting yeast they are looking for is both cold-tolerant and that it may thrive in beer wort (i.e. a very sugary liquid). With these two factors as the compass by which to orient our search, the initial focus of the expedition was on two mountain regions: Tusheti and Khevsureti. Here, the team was not only able to venture into lush native forests, but also had the good fortune to visit traditional mountain breweries. See Figure 2.

Figure 2: Historic Caucasus mountain brewery in the Tushetian village of Khakhabo (approx. 300 years old). Photo by Juan Ignacio Eizaguirre.

The head brewers not only showed the team around their brewing facilities, but also provided valuable insights into local brewing processes. In the mountainous regions of Georgia, traditional rules of conduct during the brewing process are very important, and some of them are quite strict. The team was also able to sample and taste the regional beers. See Figure 3. Most of the beers that are produced by them are refreshing and slightly sour with low carbonation. The flavour profile is clove-like and slightly fruity with a pronounced malt body. In this way, these beers are similar to other typical mountain beers insofar as they are the result of fermentation ambient temperatures in so-called fermentation houses (which can be quite cold in those mountain regions).

Figure 3: Traditionally brewed beer from the Tusheti region of the Caucasus. Photo by Juan Ignacio Eizaguirre.

Across country - over hill and dale

Some of the sites visited exhibited surprising and unexpectedly large biodiversity; the team found ancient forests with large nut, apple, pear and plum trees. It soon became abundantly clear why some call Georgia the ‘Garden of Eden’. Within two weeks, the team was able to collect about 200 samples of substrates and samples, such as soil, bark, leaves, fruits and fungi, as well as numerous samples related to the brewing process.

Figure 4: Hops samples grown at 1800 m.a.s.l.; the cultivation of yeast from hop sample in liquid medium, isolation of Saccharomyces sp. yeast on agar plat; microscopic picture of isolated yeast strain; yeast strain can be used to produce experimental Georgian, Caucasus beer. Photos by Mathias Hutzler and Margit Grammer.

Figure 5: Historic brewery sample; cultivation of yeast from brewery sample in liquid medium, isolation of Saccharomyces cerevisiae yeast on agar plat, microscopic picture of isolated yeast strain; yeast strain can be used to produce experimental Georgian, Caucasus beer. Photos by Mathias Hutzler and Margit Grammer.

The team also took samples of hops, which grow wild in the region and are also found at altitudes up to about 1800 metres. See Figure 4. The team visited four high-altitude breweries in the villages of Khakhabo, Shenako, Akhieli and Roshka, each with its own special features. See Figure 5. The journey was quite arduous even despite making use of a four-wheel drive vehicle. At one point, it took the team seven hours to cover only 70 kilometers! The route included passes at 3,000 m.a.s.l. and countless tracts of dangerous roads undivided from oncoming traffic. But it was worth it, and not only was the unbelievably beautiful panorama in the High Caucasus a constant companion on the tour, but the anthropological information we learned at our destinations were highly interesting.

Tradition and microbiology

Some of our interviews with the brewers provided exciting new insights into historical brewing and its transfer to beer today. For example, one brewer told us that he retreats to the forest (where the sacred sites of the region are located) one month before the brewing process. He purifies himself (he does not eat meat or have sexual contact). Only after this process does he return to the village. See Figure 6.

Figure 6: Mathias Hutzler taking plant samples harbouring yeast at a ‘holy site’ or ‘sacred grove’ close to the Tushetian village of Khakhabo. This was a site where brewers had to purify themselves for a period of one month before the start of the seasonal brewing process. Photo by Juan Ignacio Eizaguirre.

After our interviews, the team developed a theory that such customs could bring us closer to the question of where the yeast comes from. Men and women have different microbiomes on their skin, which can have diverse influences on the fermentation of beer in ancient processes. This can be reflected, for example, in different pH values or aroma profiles of the beers. The brewer's microbiome-- which is influenced by the nature of the ‘sacred groves’ among other things--also plays a role in the brewing process when it comes into contact with brewing utensils and raw materials. The authors suggest that, during these visits, yeast transfers took place, and the yeasts we are looking for entered the brewing process. Research is ongoing as we further test this theory in follow-up studies.

Diversity of brewing yeasts

All in all, the team was able to gather valuable information in the Caucasus to understand how the brewing process evolved, including the ingredients used and the way beer was consumed. As researchers, we were delighted with Georgia’s deep biodiversity, culture and history and the friendliness of its people in opening our eyes to the way that they all tied together. While Georgia is world famous today for the wines Georgians ferment in large clay amphorae called qvevris, it may be known for a wide variety of brewery yeasts tomorrow!


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