Raise your glass for today is International Beer Day!
This global celebration focuses on the appreciation of beer from both those who consume and produce it. As beer is a natural product of microbiology, it was only fitting that we discovered more about the beer-making process with a fermentation microbiologist. We are delighted to be joined by Dr Humberto Martín, who is an associate professor at the Department of Microbiology at the Complutense University of Madrid. He recently chaired the Fermented Beverages session at FEMS 2017. We asked Dr Martín to share his beer journey with us and his insights on how microbiology can be used to produce the best tasting beer (and ales).
How did you first become fascinated by fermented beverage microbiology?
“Although my current research is not oriented to fermented beverages but focused on studying MAPK-mediated signaling in budding yeast, fermentations have been always mysterious and engaging processes for me. I easily remember when I was a child spending my summer holidays in a small village at the west of Spain how I looked bewitched at some neighbors making their own wine, or felt so much attracted by my grandparents elaborating vinegar from the grapes they had collected at the vineyard. I think the microbiology lured my attention from those very interesting and stimulating moments. During my degree in pharmacy, taking the refreshing classes in Industrial Microbiology from Professor Martinez Peinado, I also had the opportunity to observe a fermenter happily operating full of yeast cells: I became hooked by microbiology! After completing my pharmacy degree, I had no doubts in doing my PhD under the supervision of Professors Maria Molina and César Nombela, yeast experts at the Microbiology Department of my Faculty.”
How are microorganisms involved in beer production?
“Although some beers are obtained by autochthonous fermentation by a mixture of brewery-resident bacteria and yeast, as occurring with the lambics of Belgium, or by using complex starters as inoculum, like the acid beers of Flanders, a huge proportion of the beer produced in the world is produced by using a sole microorganism: the yeast Saccharomyces. It is widely established that yeast convert the sugars present in the wort obtained from the malted barley, mostly maltose, into ethanol and carbon dioxide. However, it is less well known that they are also totally essential for the final organoleptic characteristics of the resulting fermented beverage, to the point that the strain used for the fermentation would ultimately determine the type of beer obtained.
For those that are not beer-lovers it is important to remember that two main types of beers exist: ales and lagers. In general, ales are fruity, with complex aroma (lots of esters and other volatile compounds) and they are usually consumed not very cold (around 10-15ºC). In turn, lagers are generally smooth, “clear or light tasting”, and are usually served fairly cold (2-7ºC). Ales are produced by strains of Saccharomyces cerevisiae that ferment at higher temperatures (18-24ºC) and are traditionally called top fermenters, because they tend to trap CO2 bubbles and float at the top of the vessel at the end of the fermentation process. In turn, lager strains, also known as bottom yeast, belong to Saccharomyces pastorianus, which ferment at lower temperatures (8-14ºC) and clump together resulting in flocs that settle at the bottom of the fermentation vessel. Therefore, the yeast strain has a key role in the final attributes of the produced beer.
Moreover, although hundreds of flavor-active compounds are produced along the whole process of brewing, most of them are generated by yeast during the fermentation as alcohols, acids, ketones, aldehydes and esters. The equilibrium among them is essential for the final taste of beer, and therefore the living player in beer production, the yeast, is a key factor determining flavor and aroma balance of the beer. Although yeast that belong to the genus Saccharomyces are the main players in brewing, the view that yeast are the only characters in this process is far from accurate. Microbial activity can be involved in every step of the whole process that results in beer from barley.
First, some microorganisms can be responsible for product deterioration. Fungal pathogens of barley are capable of producing micotoxins that reach the final product, and beer spoilage bacteria is a threat that exists during the whole process. Second, both bacteria and other fungi have a strong influence on the final quality and organoleptic characteristics of the product. For example, the acidification produced by lactic acid bacteria during the mashing of the malt can improve the fermentability of the wort, the foam stability and the flavor of beer. In contrast, bacterial growth during extended mashing can result in negative effects as occurring in butyric acid production by Clostridium, giving cheese-like aromas to the beer.”
What current challenges are we still facing today in fermentation beverage microbiology?
“Fermentation microbiology is currently a hot research topic in different areas. Breweries did not show too much interest in optimizing brewing yeast strains some years ago. They just employed yeasts borrowed from other companies. However, as we have learnt about the importance of yeast traits on the final product, craft beers have blossomed and revealed the huge possibilities that the use of distinct raw materials and yeast strains provide, and big brewing companies are trying to get optimized strains with improved characteristics. To this end, breeding and screening for flavor phenotypes from novel strains is the preferred approach. Although genetic engineering could be extremely useful for shaping the ideal traits of yeast strains, they would be considered as a genetic modified (GM) organism, preventing them from their commercial use. However, it is possible that the CRISPR technology, if regulations and public perception change, is not included as a GM approach and can be used in a near future for improving yeast in order to dial the production of specific aroma active compounds.
Improving the taste is also starting to be approached not only by modifying the nutritional and fermentation conditions, like temperature or pH of the fermentation performance, which has a clear effect on the production of specific compounds like aroma active esters, but also by searching in wild yeast additional flavors to the already known in classic strains. Consequently, one of the most important challenges for the future will likely be the development of screening methods for flavor perception. Those methods should identify improved yeast that, while exhibiting robust adaptation to fermentation in an industrial setting, would be able to provide enhanced characteristics to the fermented beverage.”
With the rise in interest in home brewing and mini breweries, do you think that the world is becoming more interested in microbiology?
“Craft brewing, carried out by small breweries, is offering quality and diversity of beers, and it is experiencing strong growth all around Europe. Similarly, home brewing is on the rise as the proliferation of commercial web pages offering malt or starters clearly indicate. Although it is very likely that this tendency could be already increasing societal interest in microbiology, there is no doubt that this is another good opportunity to call attention to our discipline. In this case the reason to bring the attention is not the threat of a novel emerging pathogen but a much more pleasant motive: useful microbes are getting into our homes!”