What are the main stages of coffee roasting?

Coffee roasting is a process that transforms the green coffee bean into the aromatic, flavourful coffee bean we are all used to seeing, the process usually consisting of 5 stages - although there are often more! 

Rewinding very slightly, it takes about 3-4 years for a planted coffee bush to yield fruit and when ready, coffee ‘cherries’ are harvested and dried, resulting in the green coffee, which then needs to go onto roasting. Coffee is grown in over 70 countries throughout the world, in a region known as the ‘coffee belt.’ More on that here.

Stage 1: Drying

The most common form of drying is a process known as the patio drying method. This involves spreading out the ripe harvested coffee cherries on raised beds or patios (note - this is the natural drying process. Washed or honey process uses a different method!). As the cherries dry, they are moved and turned throughout the drying process to ensure even drying and to prevent bacterial damage. The drying stage typically takes the coffee bean from a 40/50% moisture level to around 11%.

Stage 2: Browning (also known as the Maillard reaction)

Firstly, why is it called the Maillard reaction? Named after French chemist Louis Camille Maillard, the Maillard reaction is a form of browning (of foods) that typically occurs between 140-165°C. This includes many foods such as seared steaks, breads and coffee!

Throughout the Maillard reaction, sugars and proteins within the coffee react to form aroma and flavour compounds – this is where delicious coffee is born! During this stage, the coffee beans darken to a light brown, which typically lasts between 4 – 8 minutes depending on the roasting equipment used. At Beanmachines, we air-roast all of our coffee using the latest  in coffee roasting technology.

Stage 3: First Crack

Once the coffee reaches approximately 196°C the coffee will produce a cracking sound, known as the first crack. This happens when enough moisture has evaporated and the coffee bean has expanded in size. At this stage of the roasting process the coffee would be considered a light roast.

Stage 4: Second Crack

 Following on from the first crack, if the temperature (and pressure) continue to build, the cellulose structure of the coffee bean starts to break down. The coffee bean becomes significantly darker and more brittle, paving the way for the second crack. This occurs at around 224°C. Oils in the coffee bean start to migrate to the surface which gives the coffee bean a glossy, waxy look. Acidity and complexity, synonymous with a light roast gives was to more caramelised, roasted flavours. This is characteristic of dark roast profiles. 

Stage 5: Cooling

To stop the coffee from over roasting, or to halt the roasting process at a determined stage, the coffee beans must be cooled to stop the roasting process. The cooling process has a huge impact on the overall quality of the cup and is often overlooked. It is essential to properly cool  the coffee beans to maintain the unique flavour and aroma of the coffee.

On a commercial scale, coffee beans are cooled in large rotating drums, ensuring that the coffee beans are cooled down quickly which is essential to achieve the desired flavours within the coffee.