Electrochemical Profiling of Coffee Quality

Explore advancements in cyclic voltammetry as a tool for objectively measuring beverage strength and roasting levels. Based on recent research, this method decouples roast color from intensity—unlocking new opportunities for quality control and standardized evaluation.

Roast Measurement via Electrochemistry and Image Analysis: Recent Research on Coffee Roasting Progression

In recent years, electrochemistry—specifically cyclic voltammetry (CV)—has emerged as a powerful tool for objectively measuring roast progression and beverage strength. Traditional methods such as colorimetric analysis or Agtron values provide surface-level indicators of roast but struggle to capture the deeper biochemical changes that define coffee quality. New research is showing that CV can directly track the molecular transformations taking place inside the bean during roasting, offering a more precise lens on coffee chemistry.

Electrochemical Signatures of Roast Chemistry

A landmark study by Wada, Takahashi, Muguruma, and Osakabe (2021) investigated six roast levels using coffee extracts analyzed via CV on carbon nanotube electrodes. Alongside electrochemical data, the researchers quantified chlorogenic acids (CGAs) with HPLC, revealing two distinct signals:

• A reduction current near +0.27 V correlated directly with CGA concentration. As roasting intensified, CGAs degraded and the signal diminished.
• A second reduction peak at +0.10 V grew stronger with darker roasts, suggesting the emergence of new electroactive compounds—likely late-stage Maillard products or melanoidins.

The dual signal behavior highlights how CV not only tracks the degradation of antioxidants like CGAs but also reveals the formation of roast-specific compounds that influence flavor and body.

Decoupling Roast Color from Strength

The most recent leap forward comes from a 2025 preprint by Bumbaugh and colleagues, An Electrochemical Descriptor for Coffee Quality. Their work shows that CV can simultaneously measure two orthogonal parameters: beverage strength and roast level, even when visual color misleads.

By focusing on the protonic electrochemical response—the region preceding hydrogen evolution—they demonstrated that:

• Current in this region scales linearly with beverage strength (total dissolved solids).
• Suppression of protonic features over successive scans tracks roast darkness, linked to compositional changes such as melanoidin formation.

This means a roaster can now measure strength and roast independently, overcoming a long-standing challenge in coffee evaluation.

Connecting CV with Biochemistry

Earlier biochemical research provides context for what CV detects. Studies by Farah (2005), Perrone (2012), and Bekedam (2008) mapped how roasting degrades CGAs, generates lactones, and incorporates phenolic fragments into melanoidins. These transformations underpin antioxidant activity trends: lighter roasts retain CGAs, medium roasts balance antioxidant potential, and very dark roasts lose much of it.

CV mirrors these patterns: diminishing CGA peaks, the rise of new redox signals from melanoidins, and altered electrode interactions as large molecules adsorb to surfaces. The correlation between molecular chemistry and electrochemical response strengthens the case for CV as a reliable QC tool.

Practical Insights from Recent Studies

Across these investigations, several actionable themes emerge for the industry:

• Objective roast tracking: CV provides quantifiable peaks tied to CGA degradation and melanoidin growth, offering roasters a scientific gauge beyond color swatches.
• Strength vs roast independence: Electrochemical descriptors allow producers to validate marketing claims (e.g., “light but strong” brews) with objective data.
• Field and industrial application: Portable CV devices and standardized electrode protocols pave the way for on-site QC at origin and inline monitoring in large roasting plants.

Caveats and Challenges

Researchers caution that electrode material, scan rate, and brew concentration all affect results. At very dark roast levels, non-CGA compounds interfere with electrochemical signals, requiring careful interpretation. Moreover, successive scans reveal that darker roasts may suppress signals due to surface adsorption of large molecules. Standardization of methods will be crucial for industry adoption.

Toward Standardized Electrochemical QC

Together, these studies mark a turning point in how roasting is evaluated. By bridging electrochemistry with biochemical insights, cyclic voltammetry enables a dual measurement system: one axis for strength, another for roast chemistry. In doing so, it decouples roast color from beverage intensity—unlocking a more nuanced and standardized approach to quality control.

Beyond Color—Decoupling Roast Intensity from Hue

Recent Research: Electrochemical Markers Correlating with Caffeine, Acidity, and Phenolic Content

Modern studies are increasingly using electrochemical techniques—cyclic voltammetry (CV), square-wave voltammetry (SWV), modified electrodes, and related sensors—not just to detect flavor or roast color proxies, but to directly quantify components such as caffeine, phenolic compounds (including chlorogenic acids), and acidity. Below is a review of some of the most relevant recent findings, what markers have been identified, how strong the correlations are, and what that means for turning CV into an actionable QC tool.

Key Studies & Findings

1. Recent Advances in Electrochemical Sensors for Caffeine Determination — Tasić, Petrović Mihajlović et al. (2022)

What they did: Reviewed many sensor designs from ~2014 onward, especially carbon-based electrodes (glassy carbon, graphene, carbon nanotubes, etc.), often modified with nanomaterials or composites, to improve sensitivity and selectivity for caffeine.

Electrochemical markers:

• Caffeine shows well-defined oxidation peaks in CV or SWV at potentials that depend on electrode material, pH, and modifier.
• The current magnitude (I_pa, anodic peak current) is proportional to caffeine concentration; shift in peak potential can occur with interfering species or electrode modifications.

Relevance to roast / real coffee contexts: Many of the sensors are tested on beverages or extracts, but not always full roasted coffee brews. However, the findings show that caffeine is electrochemically accessible, measurable, and distinguishable with relatively low detection limits when the electrode is designed well.

2. Electrochemical Bio-Sensor of Caffeine in Food Beverages — Vinothkumar et al. (2024)

What they did: Developed a sensor using a nanocomposite (AgVO@g-C₃N) for real-time electrochemical detection of caffeine in food/beverage matrices.

Markers & findings:

• They saw clear oxidation current peaks for caffeine at particular potentials depending on buffer/pH.
• Demonstrated that even in complex matrices (other organics, possibly interfering phenolics) the sensor can quantify caffeine with useful sensitivity.

3. Simultaneous Electrochemical Detection of Caffeine, Theophylline, Guaiacol — Kushwaha et al. (2024)

What they did: Designed a modified glassy carbon electrode capable of detecting caffeine, theophylline, and guaiacol simultaneously in real samples including green coffee, coffee, and tea. Used both CV and DPV.

Markers:

• Oxidation peaks for caffeine appear in buffer around ~1.3 V, depending on electrode and modifiers.
• Linear relationships: current (oxidation) vs concentration for each analyte. For caffeine, detection limits were in the nanomolar range with good sensitivity.

Significance: Demonstrates that caffeine is electrochemically resolvable in complex beverage extracts and can be quantified even among interfering species.

4. Intelligent Electrochemical Sensor Discriminating Coffee Quality — Grasso et al. (2025)

What they did: Developed a “smart” electrochemical sensor that tested espresso samples made with beans differing in moisture content and grind size, then applied multivariate statistical methods (PCA, PLS-DA) for classification.

Markers & correlations:

• Compared electrochemical sensor signals to laboratory measurements of polyphenols, antioxidant activity, and caffeine.
• The sensor discriminated sample groups with ~86.6% accuracy.
• Results show that changes in moisture and grind affect extraction, which in turn change caffeine and phenolic content; the sensor tracked those differences.

5. Effect of Roasting Degree on Phenolics, CGA, Caffeine, Antioxidant Capacity — Jung, Gu, Lee & Jeong (2021)

What they did: Examined how roasting degree (Light-medium, Medium, Moderately Dark, Very Dark) affects total phenolics (TP), total flavonoids (TF), chlorogenic acids (CGA), and caffeine in espresso and drip coffee from Java arabica.

Findings:

• TP, TF, and CGA decrease as roasting degree increases.
• Caffeine content increases somewhat from Light-medium to Medium, then levels off or declines in very dark roasts.
• Antioxidant assays also decrease with darker roast, aligning with reduced phenolics and CGA.

How Electrochemical Markers Map to Caffeine, Acidity, and Phenolics

Component	Biochemical Behavior	Electrochemical Marker(s)	Strength of Correlation	Caveats
Caffeine	Fairly stable under roasting; increases with extraction; rises from light to medium roast, then may drop at very dark.	Oxidation peaks at ~1.2-1.4 V depending on electrode and pH; peak current proportional to caffeine concentration.	Strong: sensors achieve low detection limits and consistently distinguish caffeine in complex matrices.	Signals depend on electrode chemistry, electrolyte, and pH. Interferences possible in brewed coffee.
Phenolics / CGA	Decline sharply with roast; high in light roasts; major contributor to bitterness, acidity, and antioxidant activity.	Redox peaks at CGA potentials; suppression of acid redox/protonic features with increased roast.	Good: biochemical assays match electrochemical trends; smart sensors also correlate polyphenol content.	CGA peaks overlap; transformations in darker roasts alter signatures; electrode fouling possible.
Acidity	Generally decreases with roast as acidic compounds degrade; often tracks CGA decline.	Protonic current features before hydrogen evolution vary with acid concentration; suppression linked to roast.	Moderate: controlled studies show correlation with acid content; sensors distinguish samples by acidity.	Acidity includes many compounds; electrochemistry may capture total acid reactivity, not sensory acidity.

Deep Dive: “An Electrochemical Descriptor for Coffee Quality” (2025)

This study explicitly decouples roast darkness, strength, and composition. Using multiple electrode types and fast scan rates, the authors identified protonic features that scale with beverage strength but are suppressed as roast progresses. Even when direct detection of caffeine or CGA is complicated by the matrix, the aggregate behavior in these regions serves as proxy markers for acidity, phenolic content, and caffeine.

What This Means for QC and Roast Monitoring

• Caffeine: Quantifiable with high sensitivity if electrodes and conditions are standardized.
• Phenolics: Well-mapped declines with roast; electrochemistry provides a real-time QC marker.
• Acidity: Harder to isolate, but protonic redox regions provide useful proxies.

Composite electrochemical markers are proving more robust than trying to track every compound individually. For practical QC, integrals over potential windows can serve as effective proxies for phenolic retention, acidity, and caffeine contribution.

Limitations and Gaps

• Most caffeine studies use simplified matrices, not full brewed coffee.
• Electrode fouling and variability remain technical hurdles.
• pH and buffer conditions influence outcomes, requiring standardization.
• Sensory acidity doesn’t always equal chemical acidity; calibration is needed to link data to taste.

Summary

Recent research shows that electrochemical methods can reliably track caffeine, phenolics, and acidity in coffee. Trends include:

• Caffeine: linear oxidation peak currents, highly sensitive sensors.
• Phenolics: declining electrochemical activity with roast, aligning with antioxidant loss.
• Acidity: suppression of protonic features with roast, providing a chemical proxy for flavor changes.

These findings support the use of cyclic voltammetry and related techniques as tools for quality control, enabling more precise thresholds for caffeine, phenolic retention, and acidity—well beyond the limits of color-based roast measurement.