Agtron scale

Colour measurement scale for roasted beans (0-100). 100 = green (unroasted), 0 = black. Light roast: 70-95. Medium: 55-70. Dark: 35-55. Measured with Agtron spectrophotometer or equivalent.

Background & Context

The Agtron scale is a near-infrared (NIR) reflectance measurement system that assigns a numerical value to roasted coffee colour, providing an objective, repeatable measure of roast degree. Developed originally for the sugar industry, the Agtron Gourmet Coffee Analyzer was adapted for coffee in the 1990s in collaboration with the Specialty Coffee Association. The scale runs from 0 (very dark, almost black) to 100 (very light, green-tinged). SCA roast classifications map to the following ranges: Light (Agtron 70–90), Medium-Light (60–70), Medium (50–60), Medium-Dark (40–50), Dark (30–40), Very Dark (<30). The Agtron reading reflects the density of browning compounds (melanoidins) on the surface of the bean — not the interior. This is why most professional labs measure both whole bean and ground coffee Agtron scores: the difference between them, called the 'roast gradient' or 'development delta', reveals how evenly heat penetrated the bean. A large delta (e.g., whole bean 65, ground 45) suggests a baked roast or insufficient development time. The instrument costs $4,000–$10,000 for professional models.

Practical Use

For a roaster, the Agtron is the objective reference point for consistency across batches. If your Ethiopian Yirgacheffe tastes different batch-to-batch despite using the same roast profile, measuring Agtron on both whole bean and ground can reveal colour drift. For consumers: most specialty roasters don't publish Agtron numbers on bags, but some third-wave roasters include them in their online datasheets. A light roast Agtron above 75 typically correlates with preserved terroir and fruit notes; a dark roast below 35 correlates with roast character dominating origin.

Related Terms

Related terms: Roast development — the phase that most affects Agtron score. First crack — the key roast event before the Agtron target zone. Dark roast — typically Agtron below 35. Light roast — Agtron 70–90, the specialty coffee standard.