Buhler on the future of coffee roasting

Over the years, the technology available in roasting equipment has improved exponentially in allowing users ultimate control in creating roasted coffee. From digital controls to novel roasting methods, today’s coffee roaster – especially on the large-scale – has an unfathomable number of tools at his or her disposal to accurately recreate, time and again, a set roast profile. However, while the technology to control and recreate the roast profile has improved, operators have been largely limited to two variables in setting that roast profile: the length of the roast and the final product temperature. Dr. Stefan Schenker is the Head of Business Unit Coffee for Buhler, one of the world’s leading coffee roasting machine manufacturers, based in Switzerland. Schenker has spent the bulk of the past few years studying roast profiles, thinking outside of the box to see how the company could help improve the roasting process. “The classical way to control roasting is to control two things: the degree of the roast and the roasting time,” explains Schenker. “However when you’re only working with two parameters, you will always have limitations. For instance, you can lower your acidity with a longer roasting time, but you end up losing porosity. The only way to optimise certain characteristics is to compromise the other.” Schenker and his team’s efforts at Buhler are now set to revolutionise how roasters think with the introduction of the InfinityRoast. Unveiled for the first time at the Interpack event in Germany this past May, the InfinityRoast gives roasters control over new dimensions never before available. Through a specially designed chamber, the InfinityRoast allows users to precisely control the time/temperature curve and the air-to-bean ratio. By introducing these new dimensions via this technology, Schenker explains how roasters can create “non-traditional roast profiles”. “These new dimensions were not in focus years ago, and now they are in focus, and they offer new possibilities in extracting flavour from coffee beans,” says Schenker. The Maillard reaction is the main chemical reaction responsible for creating the chemical compounds in roasted coffee. Research has shown how the dehydration of the beans, that is the water available at each stage of the process, affects the Maillard reaction. By modifying the time/temperature curve, this modifies the dehydration kinetics of the bean, and therefore affects the Maillard reaction and flavour formation. The air-to-bean ratio similarly affects the flavour formation of the bean. This effect is most obvious in the different taste characteristics that come out of drum roasting and fluidised bed roasting.  “If you use a fluidised bed roaster, your air-to-bean ratio is very high. Similarly, if you use a drum roaster, then your ratio is very low,” he explains. Perhaps one of the InfinityRoast’s most striking characteristics is its ability to simulate air-to-bean ratios ranging from those matching drum roasters through to fluidised bed roasters. “There is no other roaster that can offer this same degree of flexibility,” says Schenker. This is possible thanks to the novel design of the InfinityRoast’s roasting chamber. The chamber is the result of four years of research and development at Buhler. “The chamber was the focus of our work, because we wanted something that would maximise process flexibility by allowing us to adapt both a high and low air-to-bean ratio,” he says. While fluidised bed roasters are praised for their lack of mechanical parts, Schenker says that in wanting to offer low air-to-bean ratios, it became clear early on that they would have to have some sort of mechanisation in the chamber to keep the beans moving. Because moving parts can cause bean breakage, the task was no easy feat. “We spent a lot of time optimising the movement in the roasting chamber. We started off with computer simulation, then we built prototypes and installed cameras to observe the beans’ movements,” recounts Schenker. “We roasted at least 150 tonnes of coffee just in the research and development phase.” The result is a ground-breaking roasting chamber design never before seen on the market;  a stationary chamber with a rotator inside. The rotator is equipped with special paddles that distribute the beans in the chamber evenly, without causing any damage. The chamber is specially designed in two parts. The lower part contains the rotator and moves the beans through a mix of mechanisation and air, while the upper part of the chamber – called the expansion chamber – slows down the air speed to move the beans back down.  It’s thanks to this hybrid that the air-to-bean ratio and time/temperature curve can be controlled to generate non-traditional roast profiles. Returning to Schenker’s earlier example of compromising acidity for porosity, he explains how these non-traditional roast profiles help an operator have the best of both worlds. For instance, a slow start profile can provide the flavour characteristics of a longer roasting time, however can maintain some pleasant acidity, while maintaining porosity. “Roasting profiles are something that I’ve studied for quite some time. The question was always, are these non-traditional roasting profiles achieving something we were not able to achieve before? After all my work, I’m now 100 per cent convinced that the answer is yes,” says Schenker. The key to controlling these roast profiles is not only having the ability to manipulate the process, but the tools to carefully monitor and adjust as needed. In this space, the InfinityRoast was carefully designed as highly reactionary. Schenker explains how Buhler technology uses what he calls “real-time” roast profiling. This means that the energy inputs into the machine are determined by the temperature of the bean. It’s like cooking a chicken with a temperature probe rather than setting the temperature on the oven. This is certainly no easy feat considering all of the possible elements that could affect the product temperature: everything from the temperature of the room, how long the equipment has been running for, and especially the varying characteristics of each coffee bean as a natural product. “With all of the InfinityRoast technology, and a chamber designed to be highly reactionary, the machine can maintain temperature stability of plus or minus one degree Celsius, even with non-traditional profiles,” says Schenker. “This is a level of stability that we have yet to see on the market.” This stability is supported by quality hardware, including a high performance burner that can modulate gas consumption very quickly. The machine also features an air bypass system that modulates how much air flows through the system. The software on the roaster is the Infinity Profile Control (IPC) system. This system automatically calculates and adjusts the energy input based on the programmed roasting profile. With even the slightest deviation from the set “master curve” the IPC system will calculate what changes are required and give a signal to the burner and air bypass system to bring the actual product temperature back to the master curve. Schenker explains that the need for this level of technology stems from major advancements in the coffee industry. This has largely been modern demands for greater process flexibility. Especially with the surge in specialty coffee, Schenker explains how modern roasting operations require equipment that can keep up with frequent recipe changes. “Many roasters are offering different blends and different origins. Each requires a different roast profile to get the most out of the bean,” he explains. This trend is only reinforced in modern trends of coffee capsule manufacturing. A single manufacturing operation may feed into different packaging lines, that each has its own time sequence and degassing requirements. As a result, modern plants need the flexibility to switch between these recipes with minimal down time. “Every time you change a recipe, the challenge is always that the first batch might be out of the norm,” says Schenker. “With quality controls getting stricter and stricter, especially when we’re talking about specialty coffee and capsules, these requirements can simply not tolerate any fluctuations in quality.” Another industry trend that is certainly leading technology developments is the need for sustainability. In this space, the InfinityRoast can hold its own. The machine uses air recirculation, saving a whopping 30 per cent on energy usage. It’s also well insulated as a standard offering, and has optimal heat transfer from the air to the bean to minimise energy usage. To deal with emissions, the system has an after burner that maintains the off-gas at 350 degrees Celsius, and is processed at this temperature via a catalytic converter. Next year, Buhler will be introducing a green coffee pre-heating system that can further decrease energy usage. After so much work to introduce this revolutionary system, Schenker is proud to say that it will already be in industrial operation this September, as the first machine was already sold as the latest edition of GCR Magazine went to print. In offering the next phase of roasting control, Schenker is confident more sales are soon to follow. 

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