Roasting graph explained
All the information you need to know about the roasting graph.
FAN
The exhaust fan percentage, which is set to 75% by default. Determines the airflow through your drum.
RPM
The main motor speed, in revolutions per minute, of the paddles moving the beans around. It is set at 55 by default.
POWER
Power is the measurement of heat entering the chamber. It shows the percentage of power applied to the heating elements.
During roasting: Adjusting the power is a way of controlling the heat entering the chamber. If controlling power manually, always monitor the other temperature parameters to understand what is going on in the chamber. The ET (air temperature) is the parameter that will change first and most quickly, so it is your best way of ensuring that the correct amount of heat is entering the chamber.
BEAN TEMPERATURE (BT)
The BT shows the surface temperature of the coffee bean mass. Several things can affect the precision of this sensor. If using less than the recommended amount of green beans (100 g), the sensor can be exposed to air, affecting the readings. If using a higher RPM, there is also a chance of the sensor being exposed to hot air.
AIR TEMPERATURE (ET)
The ET sensor measures the ambient air temperature near the drum’s center. In an automatic air temperature profile, the roaster calculates how much power to apply to the heating element so that the air temperature matches the Target.
When roasting: ET is important as it measures the convective heat available for heat transfer. It is directly affected by the power input and will react quickly to changes. When adjusting power manually, ET is the guide that shows what is happening inside the chamber. The ET will drop immediately after dumping in the coffee, as it is affected by the cold or room-temperated coffee beans. Therefore, ET is an essential measurement of how much heat is available in the chamber.
RoR
RoR stands for Rate of Rise. It shows the temperature rise the bean mass will have in the next minute, based on the change in temperature of the bean mass over the last 30 seconds.
When roasting: RoR is helpful because it tells your BT’s future. It tells you how fast or slow your roast is and how effective the heat transfer is. The RoR should decrease after the turning point (when adding the coffee in, it will take some time for the system to stabilize and the ET and BT to start rising in temperature).
CRACKS
As the bean gets hotter and water from the pores evaporates, the pressure inside the pores of the coffee bean will increase and eventually cause a crack. This is the clearest sign to tell what stage of the roasting the coffee is in. When the roaster is equipped with the first crack detection system, all the cracks appear on the graph as red lines, and the number of cracks detected will appear in brackets.
TARGET
Target is dependent on what type of profile you are using:
Air Temperature profile: Target shows us what we want the air temperature inside the chamber to be. The machine will automatically raise or lower the power to keep the ambient temperature at its target.
Bean Temperature profile: The same as an Air Temperature profile, except the target is set for bean temperature.
Power profile: The machine follows a power target and automatically adjusts the power to the set value.
The main difference between a Temperature profile (ET or BT) and a Power profile is that the roaster follows the target for either ET/BT or Power, and every other temperature parameter on the graph is an effect of that. When roasting with an Air Temperature profile or a Bean Temperature profile, the ET or BT will always follow the target, and the power will adjust to ensure it does. When roasting with a Power profile, the target decides the heat into the system, and the other two parameters will vary accordingly.
EXHAUST TEMPERATURE
A measurement of the temperature of the exhaust air. Because of its position in the chamber, it’s not an exhaust temperature sensor in a conventional way. It is there to give an additional temperature measurement from the chamber. Its position helps determine the first crack on the graph, as you can see a dip in the temperature (which is a sign of FC).
DRUM TEMPERATURE
Drum temperature measures the temperature of the outer surface of the drum.
When roasting: The drum temperature will have a much slower reaction to heat input than the ET temperature but will transfer heat to the beans through conduction.
