Section 3: Roasting

Roasting process

Green beans are sent to roasters all around the world in 60kg (132lb) sacks. Bulk supplies are transported in large containers lined with plastic. Ventilation and humidity must be carefully controlled during storage and transport to prevent bean damage. Once beans have been through the roasting and blending stages they are ready to grind and either brew or extract.

Roasting takes place in a heated rotating drum so the green beans can roast evenly. Another method is to force hot air through a screen with enough force to lift the beans which then tumble in the hot air.

Roasting has three stages:

• drying

• roasting

• cooling.

At the drying stage, green beans are placed into a drum and begin to lose moisture. The colour changes and the beans have a toasted bread smell.

As the temperature begins to rise, carbon dioxide gas builds up in the beans, the beans begin to expand and crack as the built-up gas inside escapes. When the beans first crack they are at the lightest degree of roast that can be made into coffee. As the temperature rises and the time in the barrel continues, the beans get darker and darker until they crack for the second time which indicates that they are at the darkest degree of roast.

Once the beans have reached their desired degree of roast they are removed from the heating chamber and quickly cooled to prevent further roasting. Cooling can be with cold air (dry quenching) or a fine mist of water (wet quenching). They must be cooled evenly and quickly to prevent uneven roasting. The beans continue to release carbon dioxide gas for a few days after this stage.

Degrees of Roast

There are three main degrees of roasted coffee:

• light

• medium

• dark

These can be broken down further into subcategories which are given specific names.

Light Roasts

Light roasts occur around 196ºC–209ºC (384ºF–408ºF), from a few seconds to a minute past the first crack.

The beans are light brown in colour with a dull surface.

Light roast is higher in acidity and can seem sour and grassy with the smell of baking bread. Light roasts have the lowest bitterness, highest caffeine and still have some sweetness.

Light roasts include (from lightest to darkest):

• Cinnamon

• New England

• Half city.

Medium Roasts

Medium roasts occur between 210ºC and 224ºC (410ºF–435ºF), after light roasts and up to the second crack.

The beans are medium to a rich brown with a shine occurring on the darker Full City roast. The shine occurs because of the oil being released by the beans.

Bitterness and acidity are in balance and there is an increased body. Espresso coffees that need the oils for a rich crema are usually medium-dark to dark roasts.

Medium roasts include (from lightest to darkest):

• American Roast

• City Roast

• Full City.

Dark Roasts

Dark roasts occur at the beginning of the second crack onwards, around 225ºC (437ºF) onwards.

The beans are dark brown to black and have an oily surface.

The sugars in the coffee bean have been caramelised by this point and bitterness is quite prominent with low acidity as the roast gets darker.

Dark roasts include (from lightest to darkest):

• Vienna Roast

• French Roast

• Italian Roast.