LeBrew·
Agtron Colorimeter vs. Traditional Visual Assessment: Which Is the Ultimate Judge of Coffee Roast Color?
Abstract
In coffee roasting, color change has always been a key indicator for determining the roast level. Traditionally, roasters rely on visual observation of the beans’ transformation—from the yellow-green of raw beans to light brown, dark brown, and even near black—combined with crack sounds and aroma for a subjective assessment. However, this method has significant limitations:
Strong influence of lighting: Judgments of the same batch of beans can vary greatly under daylight versus warm light.
Inability to quantify by eye: Perception of “brown” cannot be precisely graded.
No insight into internal roast uniformity: Appearance alone makes it difficult to determine the roasting consistency of the bean’s core.
To overcome these uncertainties, the Agtron colorimeter has been widely adopted in modern coffee roasting. This instrument uses near-infrared spectrophotometry, projecting light at a specific wavelength (e.g., 850 nm) onto the surface of coffee beans, measuring the reflected light intensity, and converting it into a standardized scale from 0 to 150:
Higher values (e.g., #90) indicate a lighter roast with higher reflectance.
Lower values (e.g., #40) correspond to a darker roast with lower reflectance.
For example, an Agtron reading of #55 is often regarded as an objective benchmark for a City Roast, eliminating reliance on the roaster’s experience or lighting conditions.
However, the Agtron is not infallible: for coffees such as honey-processed beans, which are rich in sugars, surface caramelization can create a darker appearance that may mislead the instrument into reading it as a dark roast, even though the actual flavor profile might still lean toward bright acidity and light sweetness.
However, the Agtron is not a flawless tool: for coffees such as honey-processed beans, which are high in sugar content, surface caramelization can darken the beans and mislead the instrument into reading them as a dark roast, even though the actual flavor profile may still lean toward bright acidity and a light, sweet character.
Objectivity and Reproducibility of Agtron Readings
In coffee roasting, consistency and standardization have always been goals pursued by roasters worldwide. The Agtron color system, with its outstanding quantifiable reproducibility, has become a foundational “flavor language” in the roasting industry.
The LEBREW RoastSee Fusion was created specifically to align with this color value system. Compared with the LEBREW RoastSee C1, it offers greater stability and higher precision, enabling roasters to judge roast levels with even greater accuracy.
1. Exceptional Measurement Stability
The Agtron system employs a sealed measurement chamber and standardized calibration tiles, ensuring that measurement discrepancies between different units are kept within ±1 unit.
Take the LEBREW RoastSee Fusion as an example:
-
Repeated measurements of the same reference sample (Agtron #55) result in a maximum deviation of only 0.5 units.
-
By contrast, visual comparison with a color tile can have an error margin of up to ±10 units.
This allows roasters around the world to “speak the same language”: Whether in New York or Tokyo, roasters—using different machines—can replicate the same nutty-chocolate flavor profile simply by targeting Agtron #65 ±1.
2. Whole Bean vs. Ground Sample: Dual-Channel Diagnostics for Roast Uniformity
The Agtron system enables dual measurements of both whole beans and ground coffee, helping to assess the roast level from the outer surface to the bean core.
| Measurement Item | Meaning | Example Value |
| Whole Bean Color | Degree of surface caramelization | 62.3 |
| Ground Sample Color | Degree of roast development in the bean core | 54.8 |
| Roast Delta (RD) | Difference between surface and internal roast levels | 7.5（=62.3–54.8） |
It introduces a key metric—Roast Delta (RD)—to quantify roast uniformity:
-
RD > 30: Often seen in certain light-roasted Ethiopian coffees, where an underdeveloped core may produce grassy notes.
-
RD < 5: Common in dark roast blends, where uniformity is high but flavor complexity may be lacking.
This “invisible parameter beyond the reach of the human eye” is a vital reference for optimizing roast curves and fine-tuning flavor profiles with precision.
Combining Two Methods to Improve Evaluation Accuracy
In coffee roasting, instruments and sensory evaluation are not opposing forces but complementary decision-making tools. In practice, a three-layer integration framework can be established:
1.Build a “Color Value–Flavor” Database
Connect numeric measurements with sensory language to enable predictable flavor adjustments.
-
After each roast, record:
-
Whole bean value / ground sample value / RD value
-
Cupping flavor notes (sweetness, acidity, aftertaste, mouthfeel, etc.)
-
-
Example record:
-
When Brazil Yellow Bourbon has an RD < 8, cupping reveals a “sticky mouthfeel.”
-
After adjusting the roast curve to raise RD to 9.5, the flavor transforms into “clearer nutty notes and a cleaner finish.”
-
-
As the dataset grows, roasters can predict: numeric change → flavor change, ultimately creating a personalized flavor control map.
2. Identify Instrument Blind Spots — Incorporating Sensory Evaluation into Quality Control
Using a dual approach of “human eye + instrument” helps to overcome technological limitations.
Although the Agtron can accurately assess color, visual assistance is still needed in the following aspects:
| Visual Feature | Issue Description | Reasons for instrument blind spots |
| Roasting Defects (Quakers) | Underripe beans develop pale yellow patches after roasting, negatively affecting flavor. | Uneven surface coloration is hard to detect through average color values. |
| Oil Presence on Surface | Dark roasts may appear glossy or dry, indicating degrees of carbonization and oil retention. | Agtron measures only color and cannot assess the physical presence or state of oils. |
3. Visual Perception Calibration: Building a “Sensory Scale”
Double-blind training helps minimize human visual error and improve consistency in roast assessment.
-
Implementation Method:
-
Roasters first visually estimate the roast level of the beans.
-
Then, they verify their judgment with Agtron measurements.
-
Through repeated training, they gradually correct sensory bias.
-
-
Case Review: In one test, five roasters misjudged anaerobic-processed beans with an Agtron value of #78 as “medium-dark roast.” The misperception occurred because caramelization from the processing method darkened the bean surface. Based on this, the team adjusted its evaluation standard: “For specially processed beans, ground sample values take precedence over whole bean values as the basis for judgment.”
Through such training, teams can establish a shared sensory standard, reduce human error, and enhance flavor consistency.
Agtron and Sensory Synergy Q&A
Q1: How can small roasteries achieve Agtron color calibration at low cost?
A1: Choosing the LeBrew RoastSee C1 is the ideal solution.
The LeBrew RoastSee C1 adopts dual-spectrum detection technology (NIR + VIS), combining precision with portability, and is highly regarded by roasters worldwide. For those seeking more advanced, all-in-one functionality, the LeBrew RoastSee Fusion can also meet professional needs.
-
Lower cost compared to CM-100 or Agtron M-Basic
-
Optional carrying case, perfect for small studios or competitions
-
Maintains high sensitivity without sacrificing accuracy for affordability
An excellent choice for budget-conscious professional roasteries striving for consistency.
Q2: Why can coffees with the same Agtron value taste different in cupping?
A2: The Agtron value reflects the roast endpoint, not the process.
The Agtron value describes only the final color after roasting, while flavor is heavily influenced by the roast curve.
Take Colombian coffee at Agtron #58 as an example:
| Development Time | Cupping Flavor |
| 60 seconds | Peanut-skin astringency, underdeveloped acidity |
| 120 seconds | Caramel sweetness with a more pronounced red-apple finish |
Conclusion: Roast development time and temperature gradient must be analyzed alongside Agtron values—color is just one part of the bigger picture.
Q3: Why do honey-processed coffees show Agtron values that don’t match their flavor?
A3: Surface caramelization can mislead the reading—ground sample values should be prioritized.
Honey-processed beans are rich in surface sugars, which easily caramelize during roasting. This often makes the whole-bean Agtron value appear lower (e.g., #55), even though the bean core still reflects a light roast flavor.
-
Solution: Rely on ground sample values
-
If the ground sample value is >75 and the RD value >15
-
The coffee should still be classified as a light roast, showing bright fruit acidity and a delicate body
-
Note: For coffees with special processing methods—such as honey or anaerobic fermentation—ground values should take precedence over whole-bean values when judging flavor.
Q4: In what situations can visual judgment not be replaced by instruments?
A4: During anomaly detection and in the fine-tuning of flavor artistry.
-
When the Agtron analyzer reports an abnormally high RD value (e.g., RD > 25), human inspection is required to check for:
-
Quakers (underdeveloped beans)
-
Uneven roasting (color blotches or scorching spots)
-
-
In competition-level roasting or delicate flavor adjustments, roasters often rely on visual cues such as:
-
Oil sheen on the bean surface
-
Roast uniformity
-
Color variations from different processing methods
-
Conclusion: Instruments and sensory evaluation must work hand in hand—neither can fully replace the other.
The finest roasters are those who know how to build a bridge between spectral data and sensory experience. When an Agtron reading signals that the RD value has crossed a critical threshold, they draw upon visual memory to anticipate potential flavor risks. And when the human eye catches a fleeting chestnut hue, they turn to numbers to validate the exact point in the process. It is through this two-way empowerment that coffee roasting evolves from an esoteric craft into a rational science.
Recommended instruments:
Have Questions or Suggestions?
If you have any feedback or would like to know more, feel free to contact us at:
service@lebrewtech.com
