Short answer
Roast colour is measured by reflecting light off ground or whole beans and reporting a number — most often on the Agtron Gourmet scale, where higher numbers are lighter. The SCAA's reference kit has eight tiles from #95 (very light) to #25 (very dark). Words such as light, medium and dark have no agreed industry definition, and different analysers use different scales, so a roast's number means most alongside the instrument that measured it.
Green coffee is pale green-grey. As it roasts it dries, turns yellow, then tan, then passes through light and dark browns as Maillard reactions between sugars and amino acids, caramelisation of sucrose and the breakdown of chlorogenic acids produce brown melanoidins. Audible milestones — first crack, second crack — punctuate the process. A 2025 study roasting three origins through seven different temperature profiles found the beans followed the same path through CIELAB colour space every time, reaching about the same colour at colour change, first crack and second crack regardless of how fast they got there.
Roast analysers shine light onto a sample and report a single reflectance-based number. The Agtron Gourmet scale is the reference most specialty roasters quote, and the Specialty Coffee Association of America produced eight visual reference tiles numbered in steps of ten from #95 to #25 for comparing ground coffee by eye. Researchers also report CIELAB values from colorimeters. Whole beans and ground coffee read differently — the inside of a bean is usually lighter than its surface — so a number is only comparable to one taken the same way.
There is no universally agreed definition of light, medium or dark roast. One study measured whole-bean Agtron Gourmet readings of about 58 for its light roasts, 48 for medium and 38 for dark across three origins, but those were that laboratory's targets, not a standard. Some roasters' light roasts are darker than other roasters' dark roasts, and competing analysers report on their own scales, so the same bag can carry different numbers depending on the device. The practical lesson is to compare numbers only within one instrument and one sample preparation.
Roast colour correlates with a great deal: acidity falls and bitterness rises with darker roasts, and roast degree affects aroma compounds, chlorogenic acid content and the colour of the brew. But two coffees with the same surface colour can taste different if one was roasted fast and one slow, because the inside and outside of the bean developed differently. Colour is a quality-control measurement for repeatability, not a complete description of a roast.
Brewed coffee colour also depends on brew strength and temperature, not just roast.
| Tile | Published label |
|---|---|
| #95 | Very light |
| #85 | — |
| #75 | — |
| #65 | — |
| #55 | — |
| #45 | — |
| #35 | — |
| #25 | Very dark |
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
ConventionModerate evidence
The SCAA roast colour reference kit contains eight colour discs numbered in increments of ten from tile #95 (very light) to tile #25 (very dark).
FactModerate evidence
There is no universally accepted industry definition of light, medium or dark roast, and roast analysers from different makers report on different scales that do not necessarily correspond.
FactModerate evidence
Across seven roast profiles and three origins in a commercial drum roaster, bean colour followed a single curve in CIELAB space, with approximately the same colour at colour change, first crack and second crack.
Caveat: One study with arabica coffee in one roaster type; validated against published literature but not yet widely replicated.
FactLimited evidence
In one study, whole-bean Agtron Gourmet readings were about 58 for light, 48 for medium and 38 for dark roasts, largely independent of origin.
Caveat: The study's own roast targets; other roasters use different numbers for the same words.
Source: Roast level and brew temperature significantly affect the color of brewed coffee
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.