By now, most coffee professionals and home enthusiasts understand the importance of TDS, a measure of the total dissolved solids that migrated from roasted coffee into the water during the brewing process. This is a way to quantify the strength of your coffee and is one of the key pieces of information when assessing your brew, and one of the reasons why refractometers are inexpensive and home user cordial, such as DiFluid R2 extract have appeared on the market in recent years.
But TDS isn’t the end all be all for flavor. There are other factors besides TDS that influence the preparation of a desirable cup of coffee, and renowned coffee researcher Dr. Christopher Hendon has developed a modern way of measuring them: electrocuting the coffee.
For his latest work published in the magazine A team of researchers from the University of Oregon, led by Dr. Hendon, sought to go beyond TDS to determine other factors that affect coffee quality. TDS only tells half the story. It tells you how much, but it can’t tell you whether the material that went into the brew is good; is unable to assess the quality. For this you need to know the chemical composition. Their working theory is that the chemical composition depends primarily on the degree of firing.
There are techniques for measuring the chemical composition of coffee, with “the gold standard being liquid or gas chromatography combined with mass spectrometry for soluble and volatile compounds, respectively,” the article says. However, these processes are ponderous, tough to prepare, exorbitant and not entirely feasible for coffee professionals.
As part of their research, Dr. Hendon and team discovered a modern, novel purpose for existing technology. Using a potentiostat, a tool commonly used in electrochemistry to test batteries and fuel cells, they sent a controlled voltage through a sample of coffee and measured the reaction. They found that less charge passed through the darker roasted coffee than the lighter roast, which they attributed to the obscure roast having a slightly higher pH and materials that were highly water-soluble.
To test their findings, the researchers tried to select a “bad batch” of roasted coffee. They were given four different roasts of the same coffee from Bath’s Colonna Coffee, one of which failed the roaster’s sensory quality control process. All coffees were visually inspected for the same color; they had Agtron scores of 92.8, 93.6, 93.9, and 98.9. Using a potentiostat, they were able to accurately determine that the 98.9 sample was out of range.
While not a tool in itself to objectively determine the quality of a cup of coffee – due to the inherent subjectivity of coffee – Hendon hopes the tool could have real-world applications in helping baristas and coffee professionals know when they have achieved their goal in a way that refractometers cannot. Once a particular coffee passes sensory evaluation and is deemed acceptable/good/outstanding, it can be rated using a potentiostat, and this reading can become a reference point for future brews. “The reason you drink a nice cup of coffee is almost certainly because you have selected a specific roast color and extracted it to the desired strength,” says Hendon Ars Technica. “Until now, we haven’t been able to separate these variables. Now we can diagnose what gives rise to this delicious cup.”
