Buhler’s real profile roasting

When it comes to achieving consistency in roasting, Stefan Schenker, Head of Market Segment Coffee for Buhler, says that the nature of coffee means the cards are typically stacked against a roaster before the process has even begun. Fluctuations in green coffee quality and moisture, the time of year (summer or winter), and the temperature of the machine can all affect the roasting process. With the degree of roast affecting extraction yields and grinding requirements, the smallest variance can have a major impact on quality. In large-scale operations, and especially capsule manufacturing, these elements become even more critical in ensuring a quality product. “For the industrial operator, the coffee they are producing must be consistent,” says Schenker. “The degree of roast is highly relevant in the flavour of the coffee as it can effect the physical properties of the bean.” The greatest challenge at this level of operation is that all the elements that must be controlled in the roasting process, despite these uncontrollable factors. The degree of roast, the roasting time, and the shape of the time/temperature curve must be accurate to develop and reproduce a specific roasted coffee product. This time/temperature curve, also known as the roast profile, is especially important in sophisticated roasting operations. “You can get to the same degree in temperature in the same time, but along a different path,” says Schenker. “It’s this path that determines the chemical reaction, and the final product.” When starting a machine cold, to get an exact roasting profile, he says that more often than not it takes a few batches to get that path lined up just right. “When the roaster is cold, getting that heat transfer right can be very challenging,” he says. “In large scale operations, the challenge also comes when you change recipes. Without special care, the first batch won’t typically meet quality standards.” To compensate for all of these challenges, Buhler has introduced a breakthrough in roasting chamber design and machine operations that can surpass these challenges, and ensure a consistent product outcome, right from the first batch. The breakthrough is a process designed by Buhler called IRC Process Control, or as Schenker calls it, “real” profile roasting. The IRC process is a highly reactive system that modulates the energy input into the system depending on the actual temperature of the bean. The result means that no matter the external factors, the same roast profile can be achieved right from the first batch. The move is a big improvement on what Schenker calls “classical” multi-step profile roasting. Used on most hot air roasters, this traditional system modulates heat according to a preset number of programmed, timed steps. “The problem with this system is that you will still have fluctuations in product temperature, batch by batch,” says Schenker. “If your exterior climate is different, if the machine is warm or cold, if the green bean moisture varies, this can all affect the roasting process. As a result, you can never get a consistent quality product.” Schenker explains that controlling the hot air temperature in the chamber alone is not enough to control the roast profile, because of the complex roasting process. The chemical reaction that occurs in the process becomes autocatalytic in the last process stages, that is producing heat unto itself, which can then affect the product outcome. Additionally, the water quenching process preferred by large‑scale roasters to stop the roasting process must be introduced very carefully. “At the end of the process, the temperatures are rising very fast, and you need to stop precisely at the right moment, not only according to time or the final temperature of the bean,” says Schenker. “You need a highly sophisticated process controlling the entire product temperature path.” The IRC system has taken this advanced approach to the controlling process. Instead of defining the energy input into the chamber, the operator defines the roasting profile by the actual temperature of the bean. “You can define what product temperature path you would like to achieve, and the roaster will control that temperature by modulating the energy,” says Schenker. While simple enough in concept, producing equipment that can achieve this “real” profile roasting has required a remarkable degree of engineering, Schenker explains. The roasting chamber must be highly reactive, with the ability to easily put more or less energy into the system. The process control software is also some of the most advanced available on the market. The advantages in the resulting product are two-fold. The first advantage is the highly desirable consistent product. The technology also offers an added bonus of being able to do non-traditional roasting profiles. “With these profiles, the time and temperature control is highly relevant,” says Schenker. “You can introduce more heat at the beginning or the end to affect the chemical reaction in a novel fashion. The result is a new profile that roasters can introduce that have never before been seen on the market.” Schenker says this level of control is available to large-scale operators, that typically work on this level of automation. “I don’t think it’s true that large-scale operators have more difficulty achieving consistency,” he says. “In fact, the contrary can be true because large-scale roasters tend to have very sophisticated tools.”