Air Temperature Measurement in Coffee Roasting

No matter how high-end the roaster is in coffee roasting, at least four temperature measurement data must be used for comparison, otherwise it will take a lot of time and beans to keep trying and erroring. The four measurement data are:

1. Inlet air temperature (inlet air temperature): the temperature of the outside air entering the combustion chamber after being heated by the fire grate and before entering the roasting barrel. Semi-hot air blowers usually measure the ambient temperature outside the air inlet hole at the bottom of the roasting barrel; direct fire machines have more holes and more air inlet points, or the ambient temperature above the roasting barrel can be used as a representative; hot air blowers can be represented by the wind temperature measurement before the hot air enters the roasting chamber.

2. Oven temperature (ambient temperature): Usually, a probe is installed in the hole on the front panel of the roasting machine. Its position will not allow the probe to contact the bean pile. The temperature measured is the temperature of the air in the roasting barrel.

3. Bean temperature (bean temperature): Usually, a probe is installed in the hole on the front panel or lower bean baffle of the roasting machine. Its position is just right for the probe to be buried in the bean pile, ensuring that most of the temperature measured is the temperature of the beans.

4. Exhaust temperature (Exhausted temperature): The probe is set on the exhaust air path, which may be at the exhaust port of the roasting barrel, in the middle of the three-pronged pipe for bean exhaust, at the rear end of the roasting machine exhaust pipe, etc., depending on the design of each manufacturer. The setting position has a huge impact on the measured value. The farther the setting position is from the exhaust port of the roasting barrel, the greater the difference in the value will be. Since the exhaust temperature is a measurement number after the roasting barrel plus the inhaled air have heat exchanged with the beans in the barrel, it is very important for the control of the roasting process. The number measured at the exhaust port of the roasting barrel has a special term MET (Maximum Environment temperature) to distinguish it from ET (Environment temperature, Exhausted temperature) set at other locations. MET is a very important measurement, especially when considering the hot air ratio of bean roasting.