the roast on track when the prescribed P setting isn’t maintaining a smooth path. I settings can be confusing, in that the higher the I value, the smaller the gain, while a low I value provides a greater output. With the control system I have in place, I don’t even have to use the D, or derivative, setting. I’m able to have enough control without adding the additional variable. It takes time and patience to establish accurate PID settings for desired roast profiles, but once the setting are locked in, very little additional tuning needs to be done. Now that I have PID settings in place, I can accurately duplicate roasts on an ongoing basis. I was surprised to learn that weather conditions such as barometric pressure and temperature have less of an effect on the process of the roast than when I attempted to control the roast manually. To compare my roast results, I pulled up roast data graphs of the same coffee profile roasted on four different days (one day near freezing, one day 80 degrees, one rainy day and one overcast day). All four roasts shadowed one another within a three-degree spread. Graph 5 shows roast profile data from four different roast days, all four being the same coffee and same profile. The top four thin lines show the environmental temperature in the roaster. It’s evident that the system was working hard to maintain the profile by looking at the range in temperatures. The wide lines represent the prescribed profile and the actual profiles of the roasts. The lines aren’t clearly visible, but there are eight lines grouped together showing the path each roast took. These graphs support the idea that roasters can replicate the roast process accurately and consistently with PID controls, without having to reset perimeters when external variables change. I’ve also discovered that PID controllers allow me to use varying charge weights of green coffee and follow the same profile, without resetting the roast perimeters. Again, the science provides consistency for me as a craftsman—within a controlled roasting environment, I can roast a 12-pound batch of coffee with the exact profile as a 24-pound batch, with the same results. I encourage roasters to invest the time and brainpower to learn how to use PID settings as a tool. It’s habit-forming, and I find I always want to try something new or make a slight change, just to see what happens. The applications seem endless to me. So many roast factors can be changed or experimented with to roast the perfect coffee and to create a roast style unique to each roaster.