The Chemistry of Beer
As summer break quickly approaches, it is that time of year when many science teachers take their love of chemistry and microbiology out of the classroom and move it to the garage for a home beer brewing adventure. Whether you enjoy brewing your own, or simply enjoy the fruits of others’ brewing efforts, the art of beer is all about science.
Some might question the scientific validity of such studies; however, beer has a place in some historically significant scientific discoveries. Some of Louis Pasteur’s bacteriology work focused on how to prevent beer from spoiling. Søren Sørensen developed the pH scale while he worked at Carlsberg Brewery. And scientists working at breweries developed methods still used today to determine protein concentrations. This industry also produced much of our knowledge of yeast genetics. In fact, brewing beer touches on so many science concepts that some collegiate chemistry departments now have elective courses—geared toward non-chemistry majors—to study the chemistry of beer brewing.
Water is the most abundant ingredient in beer; therefore, water chemistry can have a major impact on the resulting flavor, either accentuating flavor or contributing to undesirable flavor components. Different styles of beer utilize water with different hardness levels and pH, so the water chemistry must be precisely measured and adjusted. The first step that any aspiring home brewer should take is a thorough water analysis. Magnesium serves as an enzyme co-factor required by yeast in the fermentation process and must be present; however, excess magnesium can cause a bitter taste to the beer. Sodium is another ion that is involved in the flavor of beer, yet in excess, it can poison the yeast and negatively impact the fermentation process. Chlorine, which is often added to municipal water sources, should also be avoided because it can give the beer a swimming pool-like odor and corrode your beer-making equipment. Brewing salts, such as gypsum, calcium sulfate, calcium chloride, magnesium sulfate, sodium chloride, or calcium carbonate, may be added to adjust the ion levels in the water.
Yeast play a vital role in beer production and influence the flavor of the resulting product. Most beers are brewed with 1 of 2 species of yeast: Saccharomyces cerevisiae (top fermenting yeast) or Saccharomyces pastorianus (bottom fermenting yeast). Some non-Saccharomyces strains, such as Brettanomyces bruxellensis and Brettanomyces lambicus, are also used. Most commercial brewers (and a growing number of home brewers) keep the strain of yeast they use as a closely guarded secret. Identifying a strain of yeast can prove to be a difficult task, involving such skills as chromosome mapping and PCR. It is also important to keep yeast strains separate to avoid contamination; even then the strain of yeast may change over time due to selective pressures associated with the brewing process. Different strains of yeast can also have different optimal fermentation temperatures, which can certainly impact the brewing process. Oxygen, nitrogen, and sugar content all play a significant role in fermentation and need to be measured, monitored, and adjusted.
Specific gravity also plays an important role in beer production as well as the overall taste experience. A properly calibrated hydrometer measures specific gravity. The high specific gravity of the wort, due to sugars from the grains, decreases during the fermentation process as the yeast convert those sugars to alcohol and carbon dioxide; therefore, the difference between the specific gravity of the wort and that of the finished beer reveals the alcohol content of the finished beer. The specific gravity also impacts how “thick” the beer feels in your mouth.
A little science knowledge also is helpful when determining what type of container to use to store the finished beer. Beer contains iso-α-acids, which are light sensitive and break down into chemicals that produce a “skunky” taste. Storage in amber bottles, rather than those made of clear or green glass, minimizes the amount of light that penetrates the glass.
Here’s hoping you have a great summer. Cheers!