Roast Development Time Ratio Calculator

First crack is the audible split when steam ruptures the bean. Development time is the clock from that onset to drop. DTR is development divided by total roast time — many profiles aim near 20–25%. Same DTR with a crashed rate of rise is still a baked roast. Listen, log, then compute.

Inputs

Units

Results

Development time: 3.00min
DTR: 27.3%

Recommended gear

Roasting thermometer
Mark first crack on the bean-temp curve, not only by ear in a noisy garage. The clock still needs a probe.
Typical range: $20–$80
Airtight coffee canister
Development done, rest next. DTR does not replace degassing days.
Typical range: $20–$50
0.1 g coffee scale
Weigh charge and drop so DTR sits next to weight loss in the same logbook.
Typical range: $20–$80

Calculation method

Development minutes are total roast time minus time to first crack. DTR percent is that development over total time times 100. 8 minutes to crack and 11 minutes drop is 3 minutes development and about 27% DTR — a bit long for some light profiles, fine for others. If crack is after drop, the roast never developed; the numbers are invalid.

Exact formula

developmentMin = totalTimeMin − timeToFirstCrackMin. dtrPercent = 100 × developmentMin / totalTimeMin. Limits: Crack detection (ear vs temperature), lag and ‘rolling crack’ vs onset omitted; DTR is a ratio, not Agtron.

Second crack

If you hear second crack, development has gone into a darker roast level. DTR will look long; that is consistent, not a bug. Drop sooner if you wanted acidity.

Dry mill vs washed

Process changes when crack is audible as much as chemistry. Log origin and process beside DTR or the spreadsheet lies next season.

Frequently asked questions

Onset or rolling crack?

Pick one definition and keep it. Most DTR talk uses first distinct pops, not when the whole charge is roaring.

Is 20% the rule?

It is a common starting band. Nordic-style lights may sit shorter; chocolaty espresso longer. Taste the next day’s cup.

Sample roaster times are shorter.

Yes. Compare DTR within one machine and charge size. Do not copy a 5 kg profile’s minutes onto a heat gun.

Disclaimer — no professional advice, no liability

DTR does not guarantee sweetness. A 22% development on a 9-minute roast is not the same chemistry as 22% on a 14-minute roast. Use it with temperature and taste.

These calculators, pages and any related content are provided “as is” and “as available”, solely for general educational and informational purposes. They are simplified mathematical estimates, not a cupping score, a water lab report or a roasting profile, and they do not constitute professional barista, roasting, food-safety or medical advice.

Results can be wrong, incomplete or inapplicable to your grinder, brewer, beans, water or use case. You must independently verify every figure, assume all risk, and confirm on a test brew before you scale a recipe, descale a machine or change caffeine habits. Hot water, steam and espresso equipment can scald; caffeine calculators are not a substitute for medical care.

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Roast Development Time Ratio Calculator

Inputs

Results

Recommended gear

Calculation method

Exact formula

Second crack

Dry mill vs washed

Frequently asked questions

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