The Microbiology of Beer

Most beer drinkers likely don’t give much thought to the mechanics behind brewing a quality beer; yet, it is a fascinating process. A recent lecture series sponsored by the American Society for Microbiology (ASM) described the operations involved in making beer and the role microbes play in brewing beer.¹ The recent event, entitled “The Microbiology of Beer” was moderated by the American Academy of Microbiology director, Ann Reid. The first speaker, Dr. Charles Bamforth, was introduced as a distinguished professor of malting and brewing sciences at the University of California, Davis, endowed by Anheuser-Buschnhiezer and an editor of the Journal of the American Society of Brewing Chemists. In his presentation, Dr. Bamforth described beer as “the finest alcoholic beverage on the planet”, and “absolute nectar”. According to Dr. Bamforth, beer brewing typically begins with a simple cereal grain such as barley. It is malted, sprouted, dried and stored for around four weeks. Next it is ground, mixed with water and mashed. The mashed barley is boiled with hops before it is cooled, and fermented with yeast. Finally, the beer is filtered, allowed to mature and packaged. While these steps are fairly standard from one brewery to the next, getting the right balance of microbes is essential to successful brewing. Yeasts, including ale yeast Saccharomyces cerevisiae and lager yeast, Saccharomyces pastoranus, are arguably the most important microbes involved in the brewing process. A chemist by the name of Emil Christian Hansen (1842-1909) is regarded as making a large contribution to beer brewing by being the first to grow yeast in pure culture and, prior to his discovery, yeast cultures had to be shared among brewers by “back slopping” or recovering yeast from one fermentation and using it in the next. Christian was able to dilute the yeast to a single cell, which then reproduced by budding. This made it possible to fine tune the final product and get much more consistent results. Yeast impacts the quality and overall appearance of the foam, color, clarity, and haze stability of the beer. In addition, yeast also affects the flavor, the gushing- how fast and high of foam will form when it is poured, and the overall wholesomeness of the taste. There are also microbes that negatively impact the brewing process. Fusarium, for example, is a fungus common to moist climates. It can cause extensive damage to barley fields. Hydrophobins and mycotoxins such as deoxynivalenol, are secondary metabolites of these fungi which can also impact the beer. Hops plants are susceptible to microbes as well; verticillium wilt, and powery mildew are common problems. Microcontaminants in water, such as spore forming bacteria and Legionella, can also be problematic. While pesticides and chemicals can be used to treat these problems, most brewers prefer to meticulously monitor and control the entire brewing process. In her presentation, Rebecca Newman, representing Dogfish Head Craft Brewery, described the extensive network of mechanized equipment they use in their brewing process. She also stressed the importance of quality control. Their quality control team involves microbiologists that are constantly checking samples for wild yeast and other contaminants, ensuring the company’s unique flavors are consistent from one batch to the next. Reference

1. Microbe World, Microbes After Hours Podcasts, ‘The Microbiology of Beer.”