By Rachel Beebe
Coffee roasting is often romanticized as a cool, artisanal profession. The truth is, like any food service production job, the goals of a production coffee roaster are quality and consistency.
Here’s a barista analogy: Every latte made on a shift should taste the same. If the coffee tastes different—one shot more acidic, the next shot more watery, a third sweet and creamy—customers will be disappointed. Baristas use a combination of tools (scale, timer) and their palate to create a recipe. That’s called dialing in. Then they use the recipe to pull every shot of that coffee that day. Roasters do the same thing. Once we decide how a certain coffee should taste, we roast every batch to meet those taste goals.
Often, achieving consistency means doing the same thing, i.e. making the same gas and air adjustments in the roasting machine. But sometimes when you do the same things, the coffee doesn’t roast the same way. The coffee might behave differently in the roaster for any number of reasons, and deciding what to do when the coffee doesn’t behave as you expect is part of the craft of roasting.
Roasting coffee is a craft, but there’s also a lot of science to it. The beans undergo chemical changes during roasting that result in flavour changes. There’s physics and thermodynamics at play in how the beans move in the drum and in the ratio of conductive to convective heat used. And tasting coffee is an exercise in sensory science.
And, like scientists, roasters collect data. We weigh each batch before and after roasting to measure weight loss. As green coffee ages it dries out, so the same weight batch will, over time, increase in volume. So, over time, you could be putting a larger volume of coffee with a lower moisture content into the roaster.
We also measure roast colour, or how light or dark the beans are, using a light meter. Flavour correlates strongly with roast colour. A coffee roasted to a certain colour in seven minutes will taste the same (to most people) as that coffee roasted to the same colour in 10 minutes.
And the final step for QC is to taste every batch because all the data in the world can’t tell you whether a coffee tastes good. Roasting without tasting would be like painting with your eyes closed. We use a standardised method of tasting called cupping that has strict protocols covering everything from coffee to water ratio to how long the coffee brews, to how to slurp it. (check out our recent blog post that explains what 'cupping' is all about)
Ludwika once told me that when she started roasting coffee it was the first time her intensity of focus and attention to detail paid off. Having worked in hospitality her whole life, she’d been frustrated by these qualities in herself. “It seemed like everyone was telling me I cared too much and should just relax,” she recalled. But as a roaster, these attributes turned into professional strengths. Good roasters are methodical. They notice small changes and correlations, hypothesize the reasons for flavour changes and test these hypotheses to draw conclusions. Pay attention, put the time in and you’ll become a better roaster.
All this is why, at Steampunk, the roasting day starts with cupping. We taste the coffee we roasted the previous day to assess it. If we find a roast that is sweeter, complex or better in some other way, we look at the roasting data to figure out why.
On a typical roasting day, we do between 12-18 batches. We roast 6kg and 8kg batches on our 12kg-capacity Deidrich machine. After the initial warmup protocol, we preheat the roaster to about 190℃, put the coffee in and turn the burner up to 20-22 mbar gas pressure or thereabouts. We leave the heat on high until the temperature equalizes between the beans and the air in the roaster, then turn down the heat and increase the airflow incrementally until the beans reach an ideal roast level, usually within about 13 to 14 minutes.
If you’re roasting on the same type of machine at sea level (like us) and you follow these instructions, your coffee will go from green to brown. But there are a lot of ways to get from green to brown, and they don’t all taste good. To roast coffee well, you have to know your machine and you have to know your coffee.
Not all roasting machines function the same. The capacity, material, head dynamics and the type of fuel used all impact how the coffee roasts. Each roasting setup is unique because it’s a specific machine (and chimney) in a specific place. Altitude effects roasting the same way it effects any cooking, by lowering the boiling point of water. Over 10 percent of the mass of a green coffee bean is water, so roasting at altitude will be different to roasting at sea level. In addition, weather, like wind, humidity and ambient temperature can also impact roasting.
And that’s all before you put the coffee in. Coffee isn’t a monolithic, uniform product. It’s grown in roughly 70 countries around the world. There are thousands of varieties, hybrids and cultivars of Arabica, the species we roast. There are at least three distinct ways of processing the beans after they’re picked and a huge number of variations on these, all of which change the beans on a cellular level. And, coffee is an organic product that changes as it ages.
So, given all the variables, there isn’t one right way to roast. A few true things: to roast delicious coffee you have to buy high quality greens. You can’t make a low quality coffee taste better by roasting it well. You can, however, ruin a good coffee by roasting it badly. And, to roast delicious coffee, you have to be an able cupper. You need to have the skill to perceive differences between batches to know how roast data correlates to flavour.
Now I’ll put my cards on the table. I’ve never taken a professional roasting course. I learned to roast from other roasters, from reading a lot and from roasting a lot. I learned to roast skillfully by sometimes roasting badly and learning from my mistakes. If you want to be a coffee roaster, my best advice is that there aren’t any shortcuts. Get yourself into a position where you can learn from someone you respect. Then roast, taste, repeat.