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. Especially with drum
roasters, you need to be careful so that you do not burn the beans by having too much heat in the start. The drying stage is also important for
collecting energy for the bean
because the last stage of roasting is exothermic (heat producing).
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.
At the browning stage starts the Maillard reaction that is responsible for browning. This is the stage when the roast naturally slows down – and some roastmasters also want to slow it down – to ensure flavour development. In the end of browning stage the coffee starts to pop. This is called the first crack and the development stage starts.
3
ROASTING 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. If we do not slow down the roast at development stage, we easily get coffee that is smoky tasting and the flavour is too sharp.
The length of development stage is typically 15–25% of the total roast time depending on the desired flavour profile and roast degree.
