By now most coffee professionals and home enthusiasts understand the importance of TDS, the measure of the total number of dissolved solids that have migrated from the roasted coffee to the water in the brewing process. It’s a way to quantify the strength of a coffee and is one of the key pieces of information in assessing a brew, and it’s one of the reasons price-conscious and home-user friendly refractometers like the DiFluid R2 Extract have hit the market in recent years.
But TDS is not the end all be all of flavor. There are other factors that work alongside TDS to produce a desirable cup of coffee, and noted coffee researcher Dr. Christopher Hendon has devised a new way to measure them: electrocute the coffee.
For his most recent paper, published in the journal Nature Communications, a team of researchers from the University of Oregon led by Dr. Hendon sought to look beyond the TDS to determine other factors leading to a coffee’s quality. TDS only tells half the story. It tells you how much, but it can’t tell you if the stuff that made it into the brew is any good; it can’t assess quality. For that one must know the chemical composition. Their working theory is that the chemical composition is determined primarily by roast level.
There are techniques to measure the chemical composition of a coffee, “the gold standard being liquid or gas chromatography coupled with mass spectrometry for soluble and volatile compounds, respectively,” per the paper. But these processes are slow, hard to prepare, expensive, and aren’t entirely actionable for coffee professionals.
For their research, Dr. Hendon and team found a novel new purpose for existing technology. Using a potentiostat, a tool commonly used in electrochemistry to test batteries and fuel cells, they would sent a controlled voltage through a coffee sample and measure the response. They found that less charge passed through darker roasted coffee than lighter ones, which they attributed to dark roasts having a slightly higher pH and well water-soluble materials.
To test their findings, the researchers tried to pick out a “bad batch” of roasted coffee. They were given four different roasts of the same coffee by Bath’s Colonna Coffee, one of which didn’t pass the roaster’s sensory QA process. All the coffees were visually inspected to be the same color; they had Agtron scores of 92.8, 93.6, 93.9, and 98.9. Using the potentiostat, they were accurately able to determine the 98.9 sample was the one out of range.
While itself not a tool to determine objective quality of a cup of coffee—because of the inherent subjectivity of coffee—Hendon hopes that the tool can have real-world use in helping baristas and coffee professionals know when they’ve hit the mark in ways that refractometers cannot. Once a specific coffee has gone through sensory evaluation and determined to be acceptable/good/outstanding, it can be assessed using a potentiostat and that reading can become the benchmark for future brews. “The reason you have an enjoyable cup of coffee is almost certainly that you have selected a coffee of a particular roast color and extracted it to a desired strength,” Hendon tells Ars Technica. “Until now, we haven’t been able to separate those variables. Now we can diagnose what gives rise to that delicious cup.”
Zac Cadwalader is the managing editor at Sprudge Media Network and a staff writer based in Dallas. Read more Zac Cadwalader on Sprudge.
