The New Science of Roast: Why the Coffee Industry is Moving to Visible Light Measurement
From Infrared to Visible Light
Why the Coffee Industry Is Rethinking How We Measure Roast Color
For decades, roast color has been one of the most powerful predictors of how coffee will taste. Long before we had gas chromatography or advanced sensory panels, roasters learned a simple truth: color tracks chemistry. As beans brown, flavor develops. As they darken further, bitterness and carbonization take over.
Yet despite how central roast color is to flavor, quality, and consumer expectation, the specialty coffee industry has never shared a truly universal way of measuring it. That is now about to change.
According to a new white paper published by the Specialty Coffee Association, the industry is preparing to move away from infrared-based roast measurements toward a visible-light standard grounded in physics, human perception, and open science. This shift is not cosmetic. It is fundamental.
FROM THE ARTICLE, YOU WILL LEARN:
- How coffee literature and research transform professional standards.
- The move from invisible NIR measurements to human-centric visible light standards.
- Why NIR is considered a proxy rather than a direct measurement of roast color.
- The application of CIELAB (Lab*) in modern roasting technology.
- The significance of the Universal Coffee Color Curve discovered by UC Davis.
- Practical steps for baristas and roasters to adapt to these new scientific standards.
How Roast Color Is Measured Today: Near-Infrared Reflectance
Most professional roasters today rely on devices derived from the Agtron system. These instruments measure near-infrared (NIR) reflectance, typically in wavelengths between ~780 and 2500 nm.
Near-infrared light is invisible to the human eye. It interacts not only with surface color, but also with chemical bonds and internal structure. That is why NIR is widely used in agriculture and food science to estimate moisture, protein content, or fat composition.
In coffee roasting, NIR readings correlate reasonably well with roast development, which is why they became popular. They are:
- Highly repeatable
- Fast
- Robust in industrial environments
But from a physics standpoint, there is a critical limitation: NIR does not measure color. It measures how much infrared light is reflected, not how brown the coffee actually looks. Two coffees with identical visual color can produce different NIR readings depending on:
- Bean temperature
- Surface texture
- Internal porosity
- Oil migration
- Grind size
Even worse, infrared radiation is temperature-dependent. A coffee measured warm can give a different result than the same coffee measured cold, without any real change in roast development. This is why the SCA white paper explicitly states that NIR measurements should not be called “roast color” measurements at all. They are proxies. Useful ones - but proxies nonetheless.
Why Visible Light Changes Everything
Visible light occupies a different part of the electromagnetic spectrum: roughly 380 to 700 nm. This is the light humans actually see. When we describe coffee as cinnamon, medium, or dark, we are describing visible reflectance, not infrared behavior.
Modern color science already has a global standard for this: CIELAB (Lab*), developed by the International Commission on Illumination (CIE). In the CIELAB system:
- L* represents lightness (from white to black)
- a* represents green-red
- b* represents blue-yellow
Crucially, numerical distances in CIELAB correspond closely to how different colors appear to human observers. This is why the system is used in photography, printing, packaging, food quality control, and industrial design. Coffee is finally catching up.
The UC Davis Breakthrough: A Universal Color Curve
Research conducted at the UC Davis Coffee Center revealed something remarkable: when roast color is measured using visible light (CIELAB), coffees from different origins, processes, and roast styles all follow the same predictable trajectory as they darken.
This so-called universal coffee color curve shows that roast development progresses smoothly and consistently from tan to brown to black, regardless of how you get there. From a physics perspective, this makes sense:
- Maillard reactions create brown chromophores
- Caramelization deepens absorption in the blue region
- Carbonization reduces overall reflectance
The visible spectrum captures all of this directly. This finding is what enables the SCA’s proposal: a non-proprietary, visible-light roast color standard that anyone can use.
Why This Matters More Than You Think
1. A Common Language for Roasters
Today, one roaster’s “medium” is another’s “dark.” A visible-light standard allows roast color to be communicated unambiguously, across brands, countries, and roasting philosophies.
2. Better Consumer Trust
Research shows roast level is the single most influential purchasing factor for specialty coffee consumers. Standardized color measurement reduces disappointment and builds confidence.
3. Open, Device-Agnostic Measurement
CIELAB does not belong to any manufacturer. It can be measured by dedicated instruments, lab spectrophotometers, or even calibrated camera systems. This democratizes quality control.
Expert Perspective: What Roasters Should Do Now
As someone working at the intersection of physics, roasting technology, and measurement systems, here is the key point many are missing: This is not about replacing your current meter.
Infrared, visible-light color, and even digital image analysis all track the same underlying phenomenon: the progression of roast development. They simply observe it through different physical lenses. What will change is how we communicate, not how we roast.
Practical recommendations:
- Keep using your existing NIR-based tools for internal consistency
- Start correlating your profiles with visible-light color data
- Focus on repeatability, not absolute numbers
- Expect future standards to reference ranges, not single values
Most importantly: do not confuse precision with truth. A repeatable measurement that does not measure what you think it measures still has limits. Visible light brings us closer to what actually matters: what the coffee looks like, and therefore how it tastes.
The Bottom Line
The SCA’s move toward visible-light roast color measurement is not a trend. It is a correction. For the first time, roast color measurement is being aligned with:
- Human perception
- Established color science
- Open standards
- Fundamental physics
Infrared helped the industry grow. Visible light will help it speak clearly. And clarity, in specialty coffee, is long overdue.
Frequently Asked Questions
No. NIR measures infrared reflectance, which is invisible to humans. While it correlates with roast development, factors like bean temperature and texture can change NIR readings without changing how brown the coffee looks.
CIELAB numerical values correspond closely to human vision. It allows different roasters to use a common language for roast levels that is device-agnostic and based on actual human perception.
They discovered a "universal coffee color curve," showing that all coffees follow a predictable path from tan to black when measured with visible light, regardless of origin or style.
