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.

 I was paging through a home brewing catalog some fifteen years ago when I noticed green coffee beans for sale. Why did a beer supply catalog have coffee beans for sale, I wondered? This made me Google coffee roasting. One of the many ways home roasters roasted coffee was with a paint stripping heat gun (think hair drier on steroids), a bowl, and a spoon. This intrigued me. I had the equipment already, all I needed was to get some unroasted beans. I went to a local Dunn Brothers coffee shop and persuaded the barista to sell me a pound of green coffee beans. My first attempt at roasting was very iffy, but the results were better tasting coffee than I ever had. It was probably more the experience that made it better than the coffee itself. I was hooked.

 I joined some online home roasting clubs and started to purchase five pound lots of green coffee. There was a lot of good advice for a newcomer to the art of roasting. It turns out that five pounds turns to four pounds after the beans are roasted due to loss of moisture. It also turns out that the beans double in size.

  Five pounds turned into ten, and ten pounds turned into twenty. My family and friends started taking a shine to my endeavors. I couldn’t keep up with the heat gun roasting, I needed something with more volume. I purchased a perforated stainless- steel drum that went on a BBQ spit. I also needed a heat source that had the oomph to get a kilo of green beans to the proper temps required to roast. I had a “jet” burner, like a turkey fryer burner, fueled by propane. That should be plenty of heat. Now I needed to contain the heat. I sacrificed an old Weber Kettle grill. I cut the bottom off of it so it sat on the burner. I had to sit and turn the spit by hand, but this more than doubled my volume.

 After a few years on the improvised roaster, and selling roasted coffee at the local Farmers Market, I got a chance to lease time on a REAL commercial roaster - it’s capacity was six pounds. Four years later the owner purchased a larger roaster. I was roasting on a ten kilo capacity commercial roaster. I now have a one kilo roaster at home due to limitations of the Cottage Industry License that I must have to sell at the Farmers Market.

 After all the upgrades to my roasting equipment, I still think I learned more about roasting coffee from the heat gun – bowl roasting that I started on. Why? Because I had to pay attention to the sights and sounds and smells that are produced during the phases of the roast. It was relatively easy to transfer that knowledge to a commercial roaster.

To be continued………