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How to Calculate Roast Development Time

By Daniel Parodi on

Folks who roast coffee occasionally geek-out over the topic of “development time”—that duration during a roast cycle after the beginning of first crack until the coffee is discharged. This time window where crucial flavor development takes place is one of the most important details to plan and monitor.

We discuss this topic in the context of an entire roast cycle, so we don’t intend to repeat ourselves here. But the quick review is that many roasters (including us) calculate planned development time as a percentage. This “roast development” (“RD” as it is often referred to) is the target number of minutes (again, from first crack until discharge) reflected as a percentage of the entire roast cycle.

For example: you’re roasting some Mill47 Kenya Kiamabara (house favorite of ours) and first crack starts at the 7:30 mark. If we are targeting 18% RD (we like this coffee light and bright), we would calculate discharge time as follows:

7:30 ÷ (100% - 18%) or
7.5 min. ÷ 0.82 = 9.14 min or,
9:08 min total roast time

If you monitor your roasts in real time with a PC, all you need to do is click the button when first crack begins and the software does the math. If you don’t have that setup, you can refer to the quick reference chart we put together for you!

For simplicity, the chart shows RD% options of 18%, 20% and 22%. We think this is a pretty reasonable range and you should be able to extrapolate from this fairly easily if your target is outside that range.

Happy Roasting!

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