What "Light Roast" Actually Means: Agtron and How We Measure Roast Level

Walk into three coffee shops and buy three “medium roasts,” and you'll likely take home three noticeably different coffees. “Light,” “medium,” and “dark” are house dialects, not standards — one roaster's medium is another's French roast. The way out of the confusion is to stop describing color and start measuring it.

Meet Agtron

The industry's ruler is the Agtron scale — a spectrophotometer reading of roasted coffee's color, from near 0 (charcoal dark) up toward 100 (barely roasted). The machine bounces near-infrared light off a sample; darker coffee absorbs more and scores lower. Because the number comes from physics rather than vibes, an Agtron 58 in Stuart means the same thing as an Agtron 58 in Seattle. Very roughly: mid-70s and up reads light, the 60s read medium, the 50s medium-dark, and the 40s and below are properly dark territory.

Whole bean vs. ground — the two readings

Roasters actually measure twice: once on whole beans, once after grinding. The pair tells a story — if the ground reading comes out much lighter than the whole-bean reading, the roast was dark outside but underdeveloped inside (a classic sign of rushing the drying phase with too much heat). When the two numbers sit close together, the roast penetrated evenly — the goal.

How we use it

Every profile we develop gets a target color, and production batches get checked against it — alongside the roast curve, development-time ratio, and the only judge that outranks the machines: the cupping table. The Light / Medium / Medium-Dark / Dark badges you see on our site aren't guesses; they're the human-friendly translation of measurements we log batch after batch. When our sub-20% DTR habit and a target color agree, the coffee you buy in March tastes like the one you loved in January.

The takeaway

Roast level isn't better or worse in either direction — it's a flavor decision. Lighter preserves origin character and acidity; darker trades it toward body and roast sweetness. What you deserve from a roaster is that the words on the bag mean the same thing every time. Around here, there's a number behind every word.