I consider myself an experienced roaster. After seven years of roasting, I’m comfortable with my baseline knowledge and my understanding of the roasting process. However, I’m finding that today’s coffee roasting environment is one of constant change. The craft is being immersed with science, offering us new ways to unravel the mysteries of roasting, such as what really happens to the green coffee during the roasting process. The primary concepts I learned in Coffee Roasting 101 are
important in understanding the fundamentals of the roast, and it’s this base knowledge that gives me a level of comprehension as I turn my focus to new ideas and concepts of control like PID controllers. For years, I used a digital timer and temperature probe to achieve consistency in my roast profiles and had satisfactory results. But I found that I had to move out of my comfort zone of familiar techniques and terminology to learn the new skill of controlling the roast with PIDs. While this was an intimidating endeavor, my newfound roasting skills and working knowledge of PID controllers (although limited) has been rewarding and exciting. I feel that learning the scientific language and mastering the basics of PID controllers provided me with a new level of expertise. When I combine this new science with my craft, I have a new roasting tool that helps achieve a controlled path to the completion of each and every roast. Today, I control my roaster environment and the manner in which my roasts progress to the desired drop point through the logic of the PID controls. This allows me to look beyond time and temperature as the main components of the roast profile. With the PID, the S-curve becomes my tool for discovering the best path to a desired roast. To determine the most desirable roast profile, I cup various profiles of the same coffee roasted to the same degree. I alter the S-curve of each trial roast for an aggressive start or a gentle curve, for a shorter or longer rest period. When I cup the varying profiles against one another, I find that the path taken to the drop point changes the cup characteristics of each coffee, that the path itself is as critical as the time and final temperature. Initially I was overwhelmed with the entire concept of control and PID and, had I been a rookie, it could have been setback for me. Still, I attempted to break the process down to its simplest form, making this foreign concept not quite so overwhelming. I learned that the P of PID means proportional; I find it’s easier to remember as “power.” The amount of power I apply to the roast to reach the desired temperature in a pre-designated time frame. The higher I set the P value, the faster the temperature climbs. If my initial P settings are too high, the profile path is overshot and it’s difficult to slow the roast down and regain control. Once I get the P set so the roasting profile is followed consistently, I rely on the I, or integral, setting to fine-tune the roast profile. The I setting provides output boosts to keep the