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Coffee Roasting Basics Types of Coffee Roasters
Raw coffee beans or green beans are dense and lack of There are several types of coffee roasters but the most
tastes. In order to turn coffee beans in to a drink, we need to commonly used are drum roasters and fluid-bed roasters. Each
roast them. Coffee roasting is a process where heat is applied to roaster design has their strong and weak point but it plays the same
green coffee beans in order to bring out the flavors. There are role in transferring heat to coffee beans while continuously mixing
many physical and chemical reactions that occur during roast- the beans to make sure every single beans is heated evenly.
ing. For example, Maillard reactions and caramelization changes
the color of the bean from pale green to a darker brown and
creating new taste and aromatic compounds. More over, roast-
ing turns the beans from being dense and tough to be bigger in
size and brittle enough to make grinding easier and allowing hot
water to extract soluble flavors.
The Stages of Roasting

Drum Roasters
Mostly all commercial roasters are drum roasters, as
Raw Coffee Yellowing many roastery are able to roast at a slower speed. The drum
roasters consists of a cylindrical metal drum which rotates above
an open flame, moving the coffee beans while it absorbs heat by
conduction from direct contact with the hot drum and convec-
tion from the flow of air through the drum. According to Scott
Rao, the advantage of using a drum roaster is that the single pass
of the roasting gas provides a clean roasting environment, and
First Crack Second Crack the drum acts as an effective heat-storage system. It also gives a
higher consistency when roasting in larger batch size.
The process of roasting can be divided into four main
stages: The first stage is the drying phase. Usually raw coffee
has moisture content of around 9%-13%. When raw coffee is
loaded into a roaster, the beans start to absorb heat and water is
quickly being evaporated. There is little or hardly any changes
in the physical of the beans for these first few minutes of roast-
ing. Once water has been dissipated, the coffee is started to
roast. The second stage is called yellowing, where the color of
the beans starts to change from green to yellow due to the de-
composition of chlorophyll and start to smell like basmati rice
or bread. As roasting progress, the Maillard Reaction; chemical
reactions between a combination of sugars and amino acids, will
turn the beans brown and produces toasty aromas. Up to this
point, the bean is absorbing heat and building up water vapor
and gases, mostly carbon dioxide, inside the bean. As the pres-
sure inside gets too high, the bean will crack open producing Fluid Bed Roasters
‘popping’ sound and we called this stage, the first crack. The Fluid bed roasters or air roasters was invented in the
expansion of the bean causes them to double in volume and 1970s by Michael Sivetz, it consists of a tall cylinder which al-
shed silverskin or chaff, as well as developing coffee flavors. lows a stream of hot air to roast the coffee beans. The roasting
After the first crack, roaster can choose to end the roast at any process is much faster than drum roasters as more volume of
point as the acids in the beans are rapidly decreasing while the air transfers heat faster into the beans. Fluid bed roasters are
level of bitterness in increasing as the roast continues. During inexpensive and reliable. With the hot air roasting process, the
caramelization, the heat of roasting will break sugar molecules chaff is blown out of the roaster into a separate chamber and
and produces bitter flavors and the brown color deepens. The not burned up with the beans. This means that the only thing
last stage is the second crack, this is where the bean begin to that is roasted and tasted is only coffee itself. Furthermore, the
crack again and the bean will be shiny as oils begin rising to the roaster does not need to spend a lot of time and labor to clean
surface. Most of the acidity is loss and roasty flavor is present. since the vigorous bean movement keeps the roasting chamber
This denotes a full development of the coffee. wall scoured and clean to the metal surfaces.
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