The lab techniques for accurately testing the qualities of a batch of coffee are out of reach, for even the most maniacally obsessed coffee nerds in search of the perfect cuppa joe. But what if you could instead electrocute your brew to determine if it's indeed good stuff – right in the mug?
That's what chemists at the University of Oregon got up to recently, in a study detailed in Nature Communications this month. They found their simpler method goes beyond what most traditional tests reveal, while also being far quicker and easier to carry out, without the need for chemical additives or special preparation.
The current industry standard of using a refractometer to measure Total Dissolved Solids or TDS can only tell you how strong a coffee is. It cannot distinguish between a light roast and a dark roast if they have the same concentration. The team's cyclic voltammetry method for testing coffee directly in its 'as-brewed' state can measure both strength and roast color simultaneously.
To set up the electrochemical test, the researchers used a specialty green coffee from Cauca, Colombia (El Tambo). They roasted 1.75 oz (50 g) batches in-house at six different roast levels, ranging from light (75.8 Agtron) to dark (55.7 Agtron). After resting the roasted coffee for a week to allow for carbon dioxide off-gassing, the beans were ground and brewed using a 1:13.5 coffee to tap water ratio, and allowed to sit for four minutes without stirring.
After filtering the samples through V60 paper to stop the brewing process, they were cooled to room temperature. Next three small probes were placed into cups of black coffee: a platinum disk (the working electrode), a platinum wire (the counter electrode), and a silver/silver chloride reference electrode.
A machine called a potentiostat sent a range of electrical voltages through the coffee. As the voltage changed, the potentiostat measured the resulting electrical current. The amount of electrical current that flows is directly linked to how much coffee material is dissolved in the water. These signals from the coffee appeared weaker when using darker roast samples, owing to the the roast‑dependent molecules adhering to the platinum electrode during the experiment.
Unlike the conventional refractive index method, this electrochemical approach can distinguish between light-roasted and dark-roasted coffees with the same overall dissolved solids content, offering a faster, more sensitive way to assess coffee quality.
Now, you might not have a bunch of electrodes at the ready at home, but this sort of setup could be more accessible than lab equipment for commercial establishments that want to distinguish between batches of brewed coffee that look identical, but differ in flavor.
The study appeared in Nature Communications.
