Our Craft Coffee Roasting
What is craft coffee roasting? We get this question often and hopefully this will help you understand why a craft roaster is different than your standard bulk coffee producer. Simply put, craft roasting is a form of art! Here are some basic concepts that are important to know for awareness on what is occurring during the roasting process: chemical, physical, structural and sensorial.
Below are the basic stages of the roasting process after gathering as much information as possible on the green coffee beans to be used.
In order to activate the chemical and physical processes that lead to the development of the required aromas, it’s vitally important to start with a hot drum before feeding in the green coffee beans. The charge temperature depends on the amount of coffee beans introduced as well as its density and moisture. We measure the amount of beans first. In general, the starting temperature is consistent but this always depends on both the type of roasting and the characteristics of the coffee required. So, how do we find the ideal temperature? Well, we do many different tests and monitor and record what happens. We also cup a lot of coffee before we find our "profile". We always use software that monitors and records each step and adjustment. This also allows to go back and review and plan any changes needed for the next roast.
This is the moment where the coffee enters the roasting machine’s drum and is where and when the real roasting starts. During this phase the beans, which are at room temperature, absorb the drum’s heat, and temperature drops significantly. It is this endothermic phase where the coffee absorbs heat, beginning to lose some characteristics but gaining others. The main transformational changes in this phase are: an increase in bean volume and internal pressure (due to the transformation of water into steam), loss of mass and density as well as a color change from green to yellow. This last transformation marks the end of this first phase with this stark visual change. How long should it last, ideally? Generally, no less than 30% and no more than 50% of the duration of the whole roasting phase. A drying phase that is too fast will result in an uneven heat distribution inside the bean with a greater risk of external burning, scorching or tipping. While a drying phase that is too slow leads to under developed roasting resulting in a bitter, earthy taste.
DEVELOPMENT OF THE AROMAS/MILLARD/YELLOW
Here we use on our nose and ear – the smell and the sound. It is the phase where we can extract the most complex aromas by managing the time and the temperature that make up the roasting “curve”. This is the phase in which we slow down the acceleration of the temperature - its rate of rise (RoR) - in order to allow the triggering of the “Maillard reaction” and its subsequent development. The interaction between simple sugars and amino acids exposed to high temperatures allows the formation of very complex aromatic compounds. This transformation takes its name from the French chemist who first described it, Louis Camille Maillard. The end of development takes place with the famous “first crack” - a sound similar to pop-corn crackling in which the water inside, having now become steam, presses on the inner walls of the bean coming out through small crevices near the surface. We must keep balance because if we make this phase last too long we would lose the complexity of the coffee (baked defect). However, an acceleration that is too fast at this stage would not allow an adequate development of these components. Typically we want this phase around 35-40% of the whole roasting process. If we stop the roasting at the first crack, we would get what’s called a “City Roast”.
From the first crack onwards, most of what is produced is the caramelization of simple sugars. This is the so-called "development time" and is the final part of the roasting process. The more we extend this phase the more we tend to finds hints of caramel, chocolate, nutty and a buttery body, however sacrificing some sweetness. This phase ends with the "drop" of the roasted beans into the cooling tray. The results vary between a "City+" to “Full City Roast”. If we continue the roast a second crack (much quieter) occurs leading to the breaking of most of the remaining fibres in the bean and leading to the escape of CO2 together with other organic material. The results that vary between a “Full City+ Roast” to "Dark" or "French" depending on whether you stop before or during the second crack. The caramelization represents 15%-22% of the roasting phase depending again on the results we want to obtain.
Cooling is the last step and takes place outside the roasting drum in the cooling tray. It is important that the coffee beans are brought to room temperature as quickly as possible (4-5 minutes at the most). We use a high speed cooler which brings it down in 2 minutes. This is vital so that roasting does not continue which can bringing bitterness and hints of burning or baking.