1. Drying Stage
The coffee bean has a humidity of 8–12%. We need to dry it before the actual roasting starts. Drying stage typically lasts 4–8 minutes with traditional drum roaster (see below for roaster designs). The temperature in the end of drying stage is typically 160 ⁰C
2. Browning Stage
From 160 ⁰C the coffee starts to smell like toasted bread and hay. This is when the aroma precursors are starting to convert to aroma compounds. Even though browning stage is after drying stage, drying continues during the browning stage.
In the beginning of development stage the reaction becomes exothermic and the coffee cracks. During drying and browning stages the bean has collected energy that makes the coffee to explode. Development time is when the wanted aroma compounds are developing.