There’s an ancient battle raging everyday in breweries around the world. The battle is to protect your beer from dastardly bacteria that want to invade and spoil it. We’re not fighting alone, though. The yeast that ferment the beer do a lot of the antibacterial work themselves. They make beer into a pretty inhospitable environment for bacterial growth, with a low pH and lots of alcohol, but bacteria are tough little buggers. Let’s take a little journey through some of the science of beer. This post is a salute to the complex microbiology of beer and beer brewing as well as the men and women who developed and continue to develop modern brewing
No one knows exactly how beer originated, but it is thought to be the oldest fermented beverage. It is very possible that grain stocks contaminated with natural yeasts just happened to ferment, perhaps after getting wet during a flood. Eventually, some adventurous soul tasted the resulting liquid and decided it was good, maybe even great, but it is hard to believe that he or she could have realized that this discovery would change the world. The brewing of beer has been called mankind’s oldest form of biotechnology, though for most of history we didn’t understand anything about the biology behind the technology. We know that the fermenting of various grains, which I’ll generally call “brewing,” goes back at least thousands of years.
How Beer Is Made
Beer (both lager and ale) is made in a brew house. A brew house consists of a grist mill, mash tun, copper, fermenter, fermenting tanks, conditioning tanks and, usually, a kegging or bottling line. In the case of a brew pub there is no bottling or kegging so the beer is drawn to the tap directly from the conditioning tanks.
The traditional brewery (building containing a brew house) was built on at least three levels. This was done to allow gravity to do much of the work of moving the grain, grist, mash, wort and spent grains. It was also important that the fermenting and conditioning tanks be in cellars where the temperature was optimum for the fermenting and conditioning the beer.
Ale can be fermented and conditioned at higher temperature than Lager, but both need cool stable temperatures to produce the best product.
Beer preservation and hops
While hops had been used as a beer preservative for hundreds of years, the antibacterial activity of hops was not scientifically demonstrated until 1888. In 1937, a scientist named J.L. Shimwell showed that hop extracts inhibit the growth of certain types of bacteria more than others. The hop vine produces cones that, when mature, contain granules called lupulin. Lupulin are the most important components for the flavor and antibacterial properties of hops. The lupulin contain chemicals called α-acids and β-acids. The α-acids are toxic to certain types of bacteria but don’t dissolve very well in water. When the hops are boiled with the rest of the grains for brewing, the α-acids convert to iso-α-acids, which more easily dissolve into the beer. Iso-α-acids can inhibit the growth of certain types of lactic-acid producing bacteria, called “gram-positive” bacteria because of their structure. Two groups of gram-positive lactic acid bacteria, Pediococcus andLactobacillus, are responsible for the majority of beer spoilage today. The iso-α-acids of hops act as ionophores, which means they poke holes in the bacteria. This prevents the bacteria from taking up nutrients and making energy to grow and reproduce. However, some strains of these bacteria can develop resistance to iso-α-acids, just like some strains of bacteria found in human infections can develop resistance to certain antibiotics. In the same way that antibiotic-resistant bacteria are a growing concern for doctors, hops-resistant bacteria are a growing concern for brewers. Additionally, other types of gram-negative bacteria exist which are naturally resistant to iso-α-acids. Two important groups of these bacteria that are of a concern to brewers arePectinatus and Megasphaera, which are good at growing in low-oxygen environments such as a beer fermentation vat.
The future of beer
Research on how bacteria become resistant to iso-α-acids and other antibacterials found in hops and other beer ingredients is an active area of food science research. Scientists want to prevent the emergence of resistant strains and/or tackle them when they do emerge. Bacteria are relentless. Their sole goal is to survive and multiply by any means possible, even in your beer. However, as we use science to better understand the world around us, we are continually learning how better to deal with bacteria, including how to better keep them out of your beer.
Brewing is a combination of art and science, and the scientists I mentioned also made significant contributions to our understanding of wine fermentation, but wine development is too large of a topic to talk about in this post. Nonetheless, the stories of the science behind our understanding of fermentation of beer and wine are examples of how scientific research impacts many aspects of our lives, from the beverages we drink to the economic activity of the beer and wine industry. But, as in all areas of science, even with something we take for granted like beer, there’s still a lot more to learn and a lot more work to do. What we understand about the world around us is still far less than what we don’t yet understand.