How Coffee is Roasted

It seems simple. Roasting coffee is the process of turning green coffee beans into brown ones that are full of flavour. But in truth, it’s actually rather difficult.

It is a rigorous heating process that changes the physical and chemical properties of coffee beans. It is an important step in the coffee-making process because it brings out the aroma and flavour that are locked inside the green coffee beans. And this all needs to be controlled by the head roaster. This takes years of learning and experience.

During the process, some of the natural sugars are converted into CO2 gas while others are caramelised into some of the flavours that help form the complex flavours in the coffee. When the process is complete, the green bean will transform into a brown bean that is about 18% lighter while being 50 to 100% larger.

The coffee beans will also shed their outer skins, leaving behind the shell which is known as the chaff.

Since green coffee beans have a high moisture level of around 8-12%, the first stage of roasting is to dry out the moisture in the bean. The stage starts when the coffee is charged into the roaster and finishes when the coffee’s colour changes from green to yellow.

This is where the Maillard reaction takes place; it is a series of chemical reactions that are critical in developing the flavours and brown colour of roasted coffee. The internal pressure increases to the point that it can break the cell walls of the beans, causing them to pop, which is referred to as the first crack, and the development stage begins.

The final stage of the roast is responsible for the overall flavour of the coffee, depending on the roast degree and time. A colour meter can be used to measure the roasting degree, which ranges from light to dark. Lightly roasted coffees are typically more acidic, whereas dark roasted coffees are more bitter. The total roast time also affects the coffee’s flavour profile. Roasting the beans quickly produces more desired aroma compounds, but there is a risk of burning them. Slow roasting gives more control over the flavour development of the beans.

Light Roast

Light brown in colour, this roast is generally preferred for milder coffee varieties. There will be no oil on the surface of these beans because they are not roasted long enough for the oils to break through to the surface. Here at Terbodore we tend to stay away from light roasts as they don’t have much flavour development.

Medium Roast

This roast is medium brown in colour with a stronger flavour and a non-oily surface. See Mocha Java.

Medium/Dark Roast

Rich, dark colour, this roast has some oil on the surface and with a slight bittersweet aftertaste. See This is Africa.

Dark Roast

This roast produces shiny dark brown beans with an oily surface and a pronounced bitterness. The darker the roast, the less acidity will be found in the coffee beverage. Dark roast coffees run from slightly dark to charred, and the names are often used interchangeably. You do not want charred!  See The Great Dane.