What is considered an ideal DTR for light filter coffee?

For light filter coffee (single origins from Ethiopia, Kenya, Colombia), an ideal DTR typically ranges between 14.0% and 16.5%. This develops sweetness while preserving delicate floral and fruit acidity.

Why does my coffee taste grassy or like peanut skins?

Grassy, straw-like flavors indicate underdevelopment. The outer bean reached temperature, but the dense inner core failed to develop. Increase your DTR slightly by extending development time by 15-30 seconds, or slow the Drying/Maillard phases to allow heat to penetrate the core.

What is a "baked" roast fault in coffee?

A baked coffee occurs when the Rate of Rise (RoR) stalls, crashes, or goes negative after First Crack. The coffee spends too long in the drum without increasing temperature, destroying acidity and leaving a hollow, bready, flat cereal taste.

Free Coffee Roast Development Time Ratio (DTR) Calculator

☕ Roast Milestones & Timestamps

Target Roast Style Preset

Yellowing / Dry End (mm:ss)

Bean turns golden yellow ~300°F

First Crack Start (FCs mm:ss)

First audible rolling pops ~385°F

Drop / Discharge Time (mm:ss)

Released into cooling tray

Green Bean Charge Weight (g) Typical roasted weight loss: 12-18%

📊 Phase Splits & Development Ratio

Development Time Ratio 16.1% DTR = Dev Time / Total

Development Duration 1m 35s Time after First Crack

Drying Phase: 4m 30s (45.8%)

Maillard Reaction Phase: 3m 45s (38.1%)

Total Roast Duration: 9m 50s

Estimated Roasted Yield (15% loss): 425 grams

✅ Light / Nordic Roast Profile: High origin clarity, sparkling berry acidity, floral aromas.

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The Science of Coffee Roast Phase Splits

In specialty coffee roasting, taste is determined not simply by how dark the bean looks on the outside, but by how much time the coffee spends in each biochemical transformation phase inside the drum:

Drying Phase (Charge to Yellowing ~300°F): Free moisture evaporates from the raw green bean. Typically occupies 40% to 50% of the total roast.
Maillard Phase (Yellowing to First Crack ~385°F): Amino acids and reducing sugars react to synthesize hundreds of aromatic flavor compounds and melanoidin pigments that build mouthfeel body. Occupies 30% to 40% of the roast.
Development Phase (First Crack to Drop): Rapid cellular expansion fractures cell walls, releasing CO2 and caramelizing complex sugars into sweetness.

What is Development Time Ratio (DTR)?

Defined by master roaster Scott Rao, DTR represents the percentage of total roast time spent developing the bean after the first crack has commenced:

DTR (%) = (Drop_Time - First_Crack_Time) / Drop_Time × 100

Roasts with DTR below 13% risk grassy, astringent underdevelopment. Roasts with extended DTR (>25%) lose floral terroir and taste flat or baked.