tags: [] - coffee/roasting aliases: - RDR - Development ratio - Post-crack development ratio

Roast Development Ratio¶

Tags: #coffee/roasting Aliases: RDR, Development ratio, Post-crack development ratio Related: Roasting Methods MOC | Roast Profile | First & Second Crack | Heat Transfer in Coffee Roasting | Light Roast Status: ✅ Complete

Overview¶

Roast Development Ratio (RDR), also called Development Time Ratio (DTR), is the proportion of a roast's total time that occurs after first crack — expressed as a percentage of total roast time. It is a widely used roast profiling metric, introduced to specialty roasting practice by Scott Rao, that provides a consistent way to characterise the degree of post-crack development across different batch sizes, equipment, and roast curves. A higher RDR indicates more post-crack development; a lower RDR indicates less. A typical specialty coffee RDR target is approximately 20–25%, though optimal values vary significantly by coffee, equipment, and desired flavour profile.

Calculation¶

RDR = (Development Time ÷ Total Roast Time) × 100

Where: - Development Time = time from first crack to drop (end of roast) - Total Roast Time = time from charge (load) to drop

Example: A roast with a total time of 10 minutes, where first crack occurred at 8 minutes, has: - Development Time = 2 minutes - RDR = (2 ÷ 10) × 100 = 20%

Why RDR Is Used¶

Before RDR became standard in specialty roasting, roasters used Development Time alone (in minutes and seconds). The problem: Development Time is not directly comparable across different roast profiles or batch sizes. A 90-second development time on a 7-minute total roast (13% RDR) has very different implications than a 90-second development on a 12-minute roast (12.5% RDR), but more importantly differs entirely in how much chemical development has occurred relative to the batch.

RDR normalises development time, allowing meaningful comparison across profiles.

Typical RDR Values¶

RDR	Character	Notes
< 15%	Under-developed	Grassy, raw, vegetal, astringent
18–22%	Common specialty range	Clean, bright, well-developed
20–25%	Scott Rao reference range	Balanced; widely cited specialty target
25–35%	Extended development	Heavier, roastier, less bright
> 35%	Over-developed	Roasty, bitter, less origin character

These are reference ranges — not absolute rules. Light roasts of delicate varieties may perform better at 20–22%; robuster varieties or espresso blends may suit 22–25%.

Limitations of RDR¶

RDR is a useful heuristic but has limitations: - A high RDR at low absolute development time (e.g., 25% of a 6-minute roast = 90 seconds) may be very different from 25% of a 10-minute roast (150 seconds) - It does not capture what happened before first crack — the shape of the drying and Maillard phases matter - Rate of Rise (RoR) profile during development time is not captured by RDR alone - Different equipment, drum sizes, and airflow conditions produce different results at the same RDR

Key Facts¶

RDR = Development Time ÷ Total Roast Time × 100%; measures post-crack development as a proportion of total roast
Specialty reference range: approximately 20–25% (Scott Rao); varies by coffee and equipment
Normalises development time for comparison across different profiles and batch sizes
Below ~15%: under-developed (grassy, astringent); above ~35%: over-developed (roasty, bitter)
Should be used alongside Rate of Rise and absolute development time, not as a standalone metric

References¶

Changelog¶

Date	Change
2026-04-28	Note created

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