Cyclic voltammetry offers rapid electrochemical quality control for black coffee
A platinum electrode and a voltage sweep may soon replace the cupping table for routine coffee quality control. Researchers at the University of Oregon have demonstrated that cyclic voltammetry can simultaneously quantify beverage strength and roast colour in undiluted black coffee – without sample preparation – opening a credible path to instrument-based flavour assessment for the food and beverage industry.
For decades, the coffee industry has relied on two principal quality metrics: total dissolved solids (TDS), estimated via refractive index, and roast colour, measured by spectrophotometry. Neither technique captures the chemical complexity that distinguishes one roast profile from another, nor can they discriminate between batches that appear identical yet taste markedly different. A study published in Nature Communications now proposes a direct electrochemical alternative that addresses both limitations in a single, rapid measurement.
The research, led by Christopher Hendon and colleagues at the University of Oregon’s Department of Chemistry and Biochemistry, demonstrates that cyclic voltammetry (CV) – an established electroanalytical technique – can be applied to as-consumed filter coffee without modification, dilution, or the addition of supporting electrolytes. The implications for food manufacturers and roasters conducting routine quality control are considerable.
Industry limitations of existing methods
The refractive index method, currently the industry standard for estimating wt.% TDS, is inherently insensitive to solute identity. As the authors note, “the existing quantitative approach cannot discern differences between light-roasted and dark-roasted coffees that achieve the same refractive index.” This means that two chemically distinct brews – and therefore two sensory-distinct cups – can return identical readings, rendering the method inadequate for compositional discrimination.
Liquid and gas chromatography coupled with mass spectrometry can provide molecule-level detail, but are slow, expensive, and impractical for in-line or at-line quality control. Electrochemical approaches previously reported in the literature required significant sample adulteration, diluting coffee to below 0.02 wt.% TDS – nearly two orders of magnitude below filter-strength – before meaningful signals could be resolved.
How the voltammetric method works
The new approach exploits the behaviour of a platinum working electrode immersed directly in brewed coffee. When a cyclic potential sweep is applied, the cathodic features preceding hydrogen evolution – principally hydrogen underpotential deposition (HUPD) – produce a current response that scales linearly with beverage concentration. The authors confirm that “the current passed for the cathodic features that precede hydrogen evolution are linearly related to beverage strength.”
Critically, the same features are progressively suppressed across successive CV cycles as organic coffee material adsorbs onto the platinum surface. The magnitude of this suppression encodes roast information: lighter roasts, which retain higher concentrations of chlorogenic acids (CGAs) and other roast-labile compounds, produce greater suppression, whilst darker roasts – having undergone greater thermal degradation of these species – suppress the signal less. Electrochemical quartz crystal microbalance (QCM) experiments confirmed measurable mass accumulation on the electrode during cathodic sweeps, consistent with a proton-assisted adsorption mechanism.
High-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-MS) confirmed caffeine as a principal adsorbate. Density functional theory (DFT) calculations further demonstrated that 5-caffeoylquinic acid (5-CQA), an abundant CGA isomer whose concentration is strongly roast-dependent, also forms stable complexes across multiple platinum crystal facets. Together, the authors conclude that the technique “captures the ensemble of various organic adsorbates binding to the electrode surface, providing information about the beverage concentration, as well as roast colour.”
Roastery validation and quality control performance
The method’s practical utility was tested in a single-blind trial using four batches of the same coffee, sourced from Colonna Coffee in Bath, UK, all roasted to a nominal whole-bean Agtron target of 93.0 ± 1.0 units. One batch had been rejected by the roastery’s sensory panel for exhibiting undesirable flavours; its actual Agtron value was 98.9 units. Neither refractive index nor colorimetric analysis could distinguish this batch from the three accepted samples. CV analysis, however, identified sample 1 – the rejected batch – as statistically dissimilar to the others across all three scan cycles (p < 0.0039), whilst the three acceptable batches clustered within the same statistical class.
As the researchers note, the test “could help to distinguish between batches of brewed coffee that look identical and have similar dissolved-solid readings but differ in flavour.” For food manufacturers operating at scale, where batch-to-batch consistency is paramount and sensory panels are resource-intensive, this represents a meaningful advance in at-line analytical capability.
Implications for food and beverage manufacturing
The decoupling of beverage strength from roast colour within a single analytical run is the central innovation here. The authors suggest that “a series of simple CV measurements on progressively more dilute coffee will allow a roaster to rapidly construct a quality control calibration curve, enabling quantitative comparisons of separate batches of the same coffee roasted to the same colour.” The technique is also described as sensitive to seasonal crop variation and blend composition – parameters of direct commercial relevance to large-scale coffee processors and ingredient suppliers.
Brewed coffee is self-buffering to approximately pH 5 and sufficiently conductive (2–3 mS cm⁻¹) to permit direct electrochemical measurement without modification, which substantially reduces the analytical overhead compared with chromatographic methods. The cost of the green coffee used in the roasting trials was noted at approximately $10 kg⁻¹, placing the methodology within reach of smaller roasting operations as well as industrial processors.
Outlook
The study stops short of proposing a commercial instrument, but the proof-of-concept is robust. The authors conclude that the electrochemical method “offers a reliable method to measure a critical aspect of coffee composition, as well as beverage strength, simultaneously.” Future work may investigate facet-selective electrode design to improve compositional specificity, and extend the approach to espresso, cold brew, and other beverage formats where compositional variation is equally significant.
Journal reference
Bumbaugh, R. E., Pennington, D. L., Wehn, L. C., et al. (2026). Direct electrochemical appraisal of black coffee quality using cyclic voltammetry. Nature Communications, 17, 3618. https://doi.org/10.1038/s41467-026-71526-5
