In discussions of roasting technology, there’s one thing Steve Diedrich wants to make clear. “There is nothing sustainable about coffee roasting,” Diedrich says. “At least not that anyone’s really contemplated.” Working for most of his adult life in an incidental career designing coffee roasters, Diedrich’s point is rather distinct. It is difficult to view an industry that is based on the output of heat and energy to change the chemistry of a raw product as “sustainable”. It’s an interesting point from someone whose original designs, dating back to the 1980s, have turned out to be some of the most sustainable on the market. With his parents owning a coffee farm, and his brother Martin leading what used to be the giant Diedrich Coffee, Steve’s interest in the industry would seem inherent. Yet he says that he never intended to build roasting equipment, with plans to get into aeronautics engineering. This was until a certain series of events changed Diedrich’s career path. “I was just very fortunate that my first coffee roaster caught on fire,” says a straight-faced Diedrich. “So I had to build a new one.” In seeking out a new heat source for this second model, he looked no further than a few blocks down to, what was then, one of the first US manufacturers of infra-red burners. His father, Carl, told him there was no way he could build a coffee roaster with infra-red technology. A naturally defiant child, Diedrich set out to prove him wrong. Three decades later, these events proved a turning point in Diedrich’s career. In challenging industry norms by using infra-red technology, he managed to build a roaster that burns just 3 – 4 per cent of the oxides of nitrogen (NOx) gases of an equally rated blue flame burner. Other gases and emissions, including carbon monoxide (CO), carbon dioxide (CO2), sulphur oxides (SOx) and aldehyde, are reduced by an impressive 65 – 70 per cent compared to similar equipment that use atmospheric burners. With government regulations in California starting to crack down on NOx gases, Diedrich can reflect today on his rather fortunately-placed neighbour. “There is a whole new generation of roasters looking at the sustainability of their equipment,” Diedrich says. “With moves in emission controls and environmental concerns, people are really looking at the design of their roasters. Fortunately for us, a 30-year-old roaster actually exceeds the requirements that governments like California are putting in place. While other manufacturers are scrambling to meet the codes, we’re just cruising along.” Diedrich admits that his interest in reducing emissions had less to do with environmental concerns, and more to do with his interest in coffee roasting. While he initially knew little about the process, from what he had picked up from his family members, he worked out that using cleaner technology would fit well into the quality equation. “It made sense that in the chemistry of coffee, the cleaner the air, the less it would influence the chemistry change,” he says. “That’s where I really got interested in infra-red. Energy efficiency was really just secondary.” Putting quality aside for a moment, the energy efficiency of Diedrich’s technology cannot be over-stated. In looking alone at the roaster, Diedrich roasters use half the gas of blue-flame burners. “But sustainability wasn’t the main intent,” Diedrich emphasises. “What I really wanted was just to create a way to clean roast coffee.”
By using infra-red instead of blue flame, Diedrich quickly achieved his goal. Over the years, Diedrich’s design has evolved to provide unmatched control over the process. Working with mechanical engineers, Diedrich equipment employs an impressive heat exchanger that controls the airflows into the coffee. This process is important, he explains, because green coffee contains 9 to 14 per cent moisture, and this moisture acts as a good conductor for heat. Early in the roasting process, Diedrich technology allows roasters to work with this moisture content, using it to elevate sugar levels in the coffee.
The Diedrich system works moisture by controlling the airflow via a vacuum system. By decreasing the airflow early in the process, the roaster limits how much moisture is drawn out. Later on in the process, the system increases the airflow to whip out the moisture. “As the moisture reaches 100 degrees in the core of the bean, this creates tremendous energy,” Diedrich explains. “Then, working with the air, we’re able to suck the pressure out while still getting the heat into the coffee.” For the operator, to be able to control how much and when the hot air passes through the roasting system, combined with precise control over temperature, allows the user to implement sophisticated and nuanced roast profiling. Diedrich uses an apt metaphor to explain this level of control.
“Roasting coffee is a bit like steering an oil tanker,” he says. “You need to know where you’re going ahead of time, and think ahead. You can’t make any last minute turns. It’s the same with coffee roasting. If all you’re doing is turning the flame up and down, you’re not able to fully control where your roast profile is heading. Your temperature is going all over the place, and usually by the time you change it, you’re too late.” Diedrich points to four main elements as key to roast profile. The first two elements can be controlled on most conventional roasters: that is the temperature of the roast and the time frame. The third element, however, is the temperature ramping rate, that is how the temperature of the bean itself is changing throughout that time period. In raising and lowering a blue flame, Diedrich says it’s virtually impossible to accurately control this ramp rate. Because the Diedrich system is able to accurately adjust the conductive heat via the infra-red system, the accuracy is virtually unmatched. The fourth element is the ability to control the velocity of the airflow, another characteristic unique to the Diedrich system. It’s these final elements, this fine-tuning of the control, that help specialty roasters create a nuanced and repeatable roast profile. “Air is responsible for 70 to 80 per cent of the energy produced in coffee roasting,” he says. “The other 20 to 30 per cent is controlled via conductive heat. This is exactly the part we’re controlling with the roast profile, we’re working with that last 20 to 30 per cent. At the end of the day, if all you’re doing is changing the temperature, you’ll always be behind in your steering.” The process is perhaps best exemplified in the ability to roast a 200-gram sample batch of coffee on a 25-kilogram roaster. Because the energy is concentrated on the beans, the size of the roast doesn’t matter. The sustainable advantages of not requiring a sample roaster speaks for itself. Diedrich also points to is the limited temperature loss of the machine. He challenges a user to touch the top of a Diedrich roaster after nine hours of use, or measure room temperature just a few centimetres away. He assures that neither action will be affected by the heat of the roaster. “With the heat-exchangers, we’re really compounding efficiency by not losing any temperature,” he says. With just a fraction of the emissions to deal with, Diedrich has taken an interest in afterburners that use limited amounts of energy. In this end, he opts for catalytic oxidizers over thermal oxidizers. The catalytic system neutralises emissions with organic compounds, balancing out the effluence of the roaster. “With thermal systems, you’re just burning the air so you can’t see or smell the emissions, but it’s still emitting the same pollution,” he explains. “With the catalytic oxidizer, you’re actually cleaning the air.” All this is a lot talk and technological savvy for someone who only ever wanted to prove his father wrong. As Diedrich puts it, his systems have come to the point now that they are largely considered the “Rolls-Royce of the roasting industry”, the product of engineering savvy meeting incidental sustainability, with a few lucky breaks along the way. GCR
