What is Development Time Ratio in roasting?

Development Time Ratio (DTR) is the percentage of total roast time spent after first crack. It is calculated by dividing the time elapsed between first crack and the end of the roast by total roast time, multiplied by 100. A DTR between 20 % and 25 % is generally considered optimal for specialty coffee at light to medium roast: long enough to develop sugars and balance acidity without producing excessive bitterness.

First crack is the pivotal moment in roasting: under the pressure of internal steam, beans crack audibly, signalling that the cellular structure has transformed sufficiently for the beans to be potentially consumable. All time elapsed after this point constitutes the 'development phase'. During this phase, the most decisive Maillard reactions and caramelisation for the final profile take place — aromatic compound development, conversion of reducing sugars, degradation of chlorogenic acids into quinic acid (a source of bitterness), and modification of oil structure.

A DTR that is too short (below 15 %) produces an underdeveloped coffee: vegetal flavours, raw and aggressive acidity, absence of sweetness. A DTR that is too long (above 30 %) can result in a 'baked' coffee — flat, lacking liveliness — or, if development extends beyond second crack, burnt notes and carbonised bitterness. The optimal 20–25 % range is not universal: it varies with bean density, initial moisture content, variety and origin. A high-altitude bean, denser, will tolerate a longer DTR than a naturally more friable low-altitude bean.

DTR has become an essential indicator in the specialty coffee world thanks to the democratisation of roast profiling software such as Cropster, RoastPath and Artisan, which record and visualise in real time the temperature curve, Rate of Rise, and automatically calculate DTR. A little-known fact: DTR is not internationally standardised — different experts and roasters use variant definitions (some count from the start of first crack, others from the end), which can create confusion when comparing results across roasters.

DTR and roast profile