Each beer gets its unique flavor from the combination of hops, yeast, and grains used to brew it, and the chemical signatures of those ingredients can be detected using techniques such as PCR and liquid chromatography-mass spectrometry (LC–MS). So it was only a matter of time before scientists in search of the perfect pint began genetically fingerprinting beer to evaluate its quality.
“The former method is to search for useful DNA sequences, which had been reported by other researchers on beer qualities, such as protein Z and lipoxygenase,” said Ohtsubo. To improve on that approach, Ohtsubo's team created novel primers based on species-specific DNA sequences from the main ingredients in beer: barley, yeast, and hops. Using the new method, they identified 16 different barley cultivars in their samples, a feat that could improve ingredient quality control and assist brewers in selecting the best available malting barley for brewing.
Of course, Ohtsubo’s team faced other challenges with their analysis as well. For example, in the brewing process, barley, yeast, and hops contribute polyphenols, which bind with proteins to create an undesirable haze. But in the laboratory, polyphenols are even more troublesome: they bind with DNA polymerase, inhibiting PCR. To separate the DNA from polyphenols and other contaminants, Ohtsubo and colleagues used magnetic beads following the extraction of DNA by 70% ethanol from freeze-dried beer samples.
Together with 16 known primers, they developed seven novel sequence-tagged site primers, which allowed them to identify DNA from yeast, hops, barley, corn, soybean, and rice to analyze the quality of other beers. Ohtsubo's study was published earlier this month in Bioscience, Biotechnology, and Biochemistry (1).
Mass spectrometry is another tool that can be used to evaluate the quality of beer (2). “There's a lot of stuff in beer,” said Christine Hughey, an associate professor at James Madison University's Department of Chemistry and Biochemistry. “There are more than 5000 different compounds we see using liquid chromatography–mass spectrometry.”
In 2010, after drinking a pint of India Pale Ale from Danish craft brewer Mikkeller, Hughey thought: “This is a cool beer. I wonder what it would look like under the mass spectrometer.” So Hughey analyzed a line of Mikkeller beers that had been brewed in a scientific manner—all the variables had been kept constant save the breed of hops used. In that manner, Hughey was able to identify the distinguishing chemical characteristics that each hop variety imparted on the beer.
She's currently developing software that pinpoints which molecular features are unique to a particular hop in a particular year—a unique tool that will surely contribute to the growing field of beer forensics.
1. Nakamura, S., R. Tsushima, and K. Ohtsubo. 2013. A novel method for the preparation of template DNA for PCR from beer to detect materials and to develop DNA markers to evaluate the quality of beer. Bioscience, biotechnology, and biochemistry (April).
2. Colgrave, M. L., H. Goswami, C. A. Howitt, and G. J. Tanner. 2012. Proteomics as a tool to understand the complexity of beer. Food Research International (October).