I’m getting to know my new coffee roaster. It is a shiny red and stainless steel North Roaster made in China. It is a solidly built machine that has local support if it is ever needed. The roaster has four temperature probes, three of which send data to my laptop. The other is for the PID ( proportional–integral–derivative ) control on the control panel. A common example of a PID is the cruise control on a car. This one shows bean temperature and, as an added safety feature, is connected to an automatic system shut down if the it reaches a preset temperature. The software on the laptop is Artisan roasting software, which logs five sets of data that the three probes send to the computer.

1.    Environmental temperature. This is how hot the air is in the drum.

2.    Bean temperature. This is the temperature of the bean mass.

3.    Incoming air. How hot the air is that feeds the drum.

4.    Delta Bean temperature. This calculates the “rate of rise” of the beans, which is how fast the beans are heating up.

5.    Delta Environmental temperature. This is the rate of rise in the air mass of the drum.

Numbers 4 and 5 are computer calculations from samples taken at three second intervals and are used to calculate certain markers in the roast such as

1.    End of drying. The point where the beans start turning yellow as the moisture content of the beans declines.

2.    First crack. This sounds like popcorn popping. The first of two sounds the beans themselves make during the roast when the coffee bean has expanded and its moisture begins to evaporate. This moisture forms steam, and then pressure, that forces the beans to crack open.

3.    Second crack. This is more of a Rice Crispies snap-crackle-pop. The cellular matrix of the bean actually fractures here, allowing oils to migrate outward.

This is a sample of what the graph looks like.

Green is incoming air temp

Red is environmental temp

Dark Blue is bean temp

Lighter Blue is delta bean temp or rate of rise of bean temp

Gold is delta environmental temp or rate of rise in air temp

  

This is not automation. I still control the heat and the airflow. It is just a way to record a set of data points that you can try to duplicate. All these factors combine to determine what the coffee will taste like.