What is Development Time Ratio (DTR) in coffee roasting?

Development Time Ratio - abbreviated DTR - is the percentage of total roast time that falls within the development phase: from first crack to drop. It's calculated simply as development time divided by total roast time, expressed as a percentage.

For example: a roast that takes 10 minutes total, with 2 minutes from first crack to drop, has a DTR of 20%.

DTR has become one of the most widely referenced metrics in specialty roasting because it provides a comparable, relative measure of development that accounts for differences in total roast time. Two roasts with the same absolute development time of 2 minutes may be very different if one had a total roast time of 8 minutes (DTR 25%) and the other 12 minutes (DTR 17%).

A commonly cited target range for specialty roasting is 20-25% DTR, though this varies meaningfully by coffee, machine, and target profile. More important than hitting a specific number is understanding what your DTR is telling you - and using it alongside end temperature, RoR at drop, and of course the cup itself to diagnose and refine your profiles. DTR alone doesn't guarantee a well-developed roast, but it's a useful consistency checkpoint that most roasting software calculates automatically.