Evaluating coffee quality by electrochemical methods: Cyclic Voltammetry opens up a new direction for quality control

Two cups of coffee with the same TDS index are not necessarily the same in terms of flavor. One cup may be roasted light, rich in acidic characteristics and fruity flavors, while the other cup may be roasted dark, with a different body and a more pronounced bitter taste. However, if only a refractometer is used to measure the total dissolved solids, the roaster may receive very similar numbers.

This is an important issue in coffee quality control: measuring dissolved solids does not necessarily mean understanding the full chemical composition of the beverage.

A study published on April 28, 2026, in Nature Communications has introduced a new approach. Scientists used the cyclic voltammetry method, also known as Cyclic Voltammetry (CV), to evaluate both the density of the beverage and some related component characteristics at the same time.

This study is notable because it not only seeks to measure a single compound such as caffeine or chlorogenic acid, but also exploits the overall electrochemical reaction of multiple components in the same coffee sample.

1. Why is the TDS index not enough to evaluate coffee quality?

TDS (Total Dissolved Solids) is the ratio of total dissolved solids in the beverage. In the coffee industry, a refractometer measures the refractive index of the solution and uses a calibration model to estimate TDS.

For example, when measuring filtered coffee, the device may display a TDS of 1.35%. This means that approximately 1.35% of the beverage's weight is estimated to be dissolved solids.

This index is very useful for controlling density and extraction efficiency. When combined with the coffee dry matter dosage and beverage weight, the brewer can calculate the extraction yield.

However, there is a limitation: a refractometer does not accurately determine each compound in the solution. Different dissolved solids can contribute to the refractive index signal in different ways.

Two coffee samples with the same TDS may differ in:

• The amount and ratio of organic acids.
• Caffeine and related compounds.
• Polyphenols, especially the chlorogenic acid group.
• Compounds formed in the Maillard reaction and thermal degradation.
• The dissolved solid composition changes depending on the origin, processing, and roasting level.

Therefore, TDS describes the overall density but does not provide sufficient information about the chemical nature that gives rise to the sensory experience.

2. How does Cyclic Voltammetry work?

Cyclic Voltammetry is an electrochemical analysis method, in which the potential is scanned in one direction and then reversed over a specified range. During this process, the device records the current response between the electrodes and the solution.

For the 2026 coffee research, the system used three electrodes:

• Working electrode: Platinum (Pt) disc, where the electrochemical reactions being monitored occur.
• Counter electrode: Platinum wire, completing the electrical circuit.
• Reference electrode: Ag/AgCl saturated with KCl, providing a stable potential reference.

A potentiostat controlled the potential between the electrodes and recorded the current response.

In the study, the researchers did not focus on quantifying caffeine or a specific acid in the raw coffee sample. They monitored the signal region related to hydrogen adsorption on the Platinum surface and proton reduction before gas formation.

Notable feature is that this signal changes with the concentration of dissolved substances and the chemical composition of the coffee.

3. Why does roast color affect the electrochemical signal?

The Platinum electrode surface has the ability to interact with organic molecules in the coffee. When the sample is scanned through multiple cycles, a portion of the coffee material accumulates on the electrode surface, reducing the number of active sites that can participate in the reaction.

This phenomenon is called electrode fouling, which can be understood as the decrease in surface activity due to material deposition on the electrode.

The study found that caffeine is present in the adsorbed material. Chemical simulations also showed that caffeine and 5-caffeoylquinic acid (5-CQA), a chlorogenic acid isomer, can interact with Platinum crystal faces.

This helps explain why the chemical composition of the coffee can change the electrochemical signal over repeated scans.

During roasting, caffeine is not the only component that determines this change. Chlorogenic acid, heat-altered products, and other organic compounds also contribute to the overall reaction of the sample.

4. Experimental results: How do light and dark roasted coffees differ?

To check the effect of roast level, the research group used a specialty Arabica coffee from El Tambo, Cauca, Colombia.

The samples were roasted to six profiles by gradually increasing the development time and final temperature. The results obtained a color range from 75.8 Agtron in the lightest sample to 55.7 Agtron in the darkest sample.

After roasting, the samples were left to rest for seven days to release CO2, then brewed using the SCA cupping method.

To separate the effect of roast color, the samples were diluted and standardized to a TDS level of 1.00 ± 0.02% before measurement.

Notable result is that the lightest roasted sample produced a current passing through the signal region studied about 50% higher than the darker roasted samples at the same TDS level.

This shows that two samples with the same density measured by refractometer can still produce different electrochemical reactions due to differences in chemical composition after roasting.

It is essential to emphasize that a 50% difference is a result of the sample set and specific experimental conditions. This ratio cannot be applied as a rule for all coffee varieties, growing regions, or roasting machines.

5. Experiment to distinguish between successful and unsuccessful roasts

The most practical part for the roaster lies in the quality control test performed together with Colonna Coffee, a specialty roaster in Bath, UK.

The research team received four batches of the same coffee, produced by the roaster according to a target green bean color of approximately 93 ± 1 Agtron.

Out of the four samples:

• Sample 1 had a color of 98.9 Agtron and was rejected by the roaster due to being too light, accompanied by unsatisfactory sensory characteristics.
• Sample 2 achieved 93.9 Agtron.
• Sample 3 achieved 92.8 Agtron.
• Sample 4 achieved 93.6 Agtron.

Each sample was prepared five times in random order and evaluated using electrochemical methods.

The results showed that all four samples had TDS values that were statistically insignificant. Color measurement and refraction also failed to clearly distinguish the rejected batch from the accepted batches.

In contrast, the electrochemical signal in the initial cycle indicates that sample 1 is significantly different from the other three samples. Upon comparison with the information from the roaster, the researchers correctly identified the sample to be discarded.

6. Can voltammetry replace a refractometer and cupping?

At present, the answer is no.

The refractometer still has a significant advantage in terms of convenience, measurement speed, and implementation in coffee shops or roasters. It provides the necessary data to track TDS and extraction efficiency.

Agtron or color meters are still useful for controlling roast color. Cupping still plays a role in directly evaluating sensory attributes that a comprehensive electrochemical signal cannot fully describe.

Voltammetry has the potential to add another layer of information: electrochemical reactions are sensitive to the total chemical composition of the beverage sample.

7. Limitations to be aware of before applying to a roaster

Although the research results are very noteworthy, there are still some technical issues to be addressed before this method can be introduced into the normal production process.

The measuring device is still laboratory-based

The research used a potentiostat, a three-electrode system, and a carefully prepared Platinum electrode. This is not a simple configuration equivalent to a handheld refractometer.

Electrode fouling

Electrode fouling is indeed a part of the signal that researchers exploit, but it also creates a requirement for cleaning and standardizing the electrode state between measurements.

The calibration curve may depend on the type of coffee

The authors note that the shape of the relationship between charge, TDS, and roast color may be specific to each type of coffee. Therefore, a suitable calibration curve should be developed rather than applying a set of common parameters for all origins.

Need to be verified by multiple brewing methods

The main experiment used the cupping method and some controlled roast samples. Additional research is needed on espresso, phin, pour-over, cold brew, and other brewing methods to determine the potential for application.

The study also discloses that the two authors have a financial interest in Overpotential, a company developing electrochemical technology applied in food. This information should be noted when evaluating the study, although the paper has undergone scientific peer review.

Significance to the coffee roasting industry

The value of the study lies not in creating another index for roasters to pursue, but in the ability to recognize chemical differences that standard measurements may miss.

In specialty coffee production, two batches may have similar colors, similar TDS after brewing, but still differ in composition and sensory experience.

If Voltammetry is developed into a high-repeatability measurement system with easy calibration and suitable cost, this method could support quality control by batch, track the stability of blends, and detect deviations that colorimetry or refractometry may not detect.

For roasters, a reasonable direction now is to view electrochemistry as a research tool and quality control supplement, not a replacement standard for TDS, Agtron, or cupping.

References

1. Bumbaugh RE, Pennington DL, Wehn LC, et al. (2026). Direct electrochemical appraisal of black coffee quality using cyclic voltammetry. Nature Communications, 17, 3618. Published on 28/04/2026. DOI: 10.1038/s41467-026-71526-5.
2. Nature Portfolio (2026). Brewing up a quick test for great coffee. Explanation of research results and potential applications. Nature Asia.
3. Guinard JX et al. (2023). A new Coffee Brewing Control Chart relating sensory properties and consumer liking to brew strength, extraction yield, and brew ratio. Journal of Food Science. Tra cứu DOI.
4. Specialty Coffee Association. Specialty coffee technical documents and standards