Today let’s talk about some of the variables in coffee roasting. The essence of roasting is that the roaster conducts heat energy to green coffee beans to make them dry and mature, and a series of physical and chemical changes occur in the process.
Variable One: Heat Energy
The heat energy of the roaster is the heating method of the roaster. Take our company’s equipment as an example, it is a “semi-direct fire and semi-hot air roaster”, which is based on heat transfer and uses hot air as an auxiliary heating method.
A short testing video shows the heating method of our coffee roasters: https://youtu.be/jjGAHMGUO6g
The biggest feature of this heating method is that the thermal energy has a strong penetrating power, which can quickly penetrate the structural fibers of the green coffee beans and send the heat into the deep bean core. Thereby alleviating the problem of excessive temperature rise rate difference between raw beans surface and bean core.
Variable two: Dehumidification
During the dehydration stage of roasting, a large amount of water in the green beans is discharged in the form of water vapor. At this time, the water vapor will hinder the heat transfer between the surface of the green beans and the bean core. As a result, the heating rate suddenly drops sharply, but generally returns to normal values after a short period of time.
At this time, we must pay attention to the humidity changes in the roasting room. Once the humidity is too high, we need to increase the airflow in time to discharge excess water vapor.
Variable three: Smoke Exhaust
Generally speaking, when the coffee roasting temperature reaches 180°C, the amount of smoke produced will start to become obvious. The amount of smoke increases sharply at the beginning of the first crack and reaches the peak at the second crack. The darker the roast, the greater the amount of smoke. Therefore, the smoke exhaust problem of coffee roasting from the first crack to the development stage must be done properly.
If the cell wall of the coffee beans is opened when they burst if the smoke is not exhausted with a large airflow in time, the soluble substances in the cells will be attached to the smoke, and the coffee flavor will be affected by it, resulting in the so-called “smoke”.