Roasting Coffee

Matt Kelly,

Roasting Coffee: What’s the big deal?

Story and photos by Matt Kelly

“If we don’t roast coffee, we really can’t drink coffee,” say Ben Turiano, co-owner and bar manager at Joe Bean Coffee Roasters in Rochester. In front of him is the shop’s roasting machine: a steampunk beast of shiny metal, curves and angles, pipes and dials, and a Vegas-style lever. There’s a little door that swings open to reveal blue flames in its belly. And up top is the hopper where a batch green coffee beans waits to go in.

Matt Kelly,“Roasting coffee means radically changing a bean,” Ben says. “We dry it and give structure to the cellulose. This allows us to grind the bean into small particles so we can pour water through it and pull flavors out of it.” Roasting is a matter of practical efficiency; trying to grind “wet” beans is anything but practical or efficient. But roasting also serves another critical purpose: creating taste.

“By roasting coffee we’re manipulating the flavors we experience when drinking it. And this is where things start to get fun,” Ben says.

This is also where things start to get nerdy.

The beans drop from the hopper into a large drum rotating over the flames. A fan pulls air through the drum to apply heat primarily through convection, ensuring the roasting is consistent and even. The beans tumble round and round as they go from green to brown.

Roasting coffee involves two main considerations: temperature and time.

It used to be that roasters only considered end temperatures and how they resulted in beans that were lighter or darker in color. Different colored beans tasted different and this is what led people to describe beans in some very general terms like dark roast, medium roast, cinnamon roast, city roast, and so on. Not extremely useful in describing the actual flavor you’re going to get.

But then roasters started paying attention to how timing made a difference in the process. Bringing beans to 415° in 10 minutes creates a radically different taste than if you hit the same end temperature in 20 minutes. Roasters started to notice that spending different amounts of time at different temperatures before hitting the end point also changed the taste. A wide range of flavors and aromatics could appear in the final beverage: tangerine, blackberry, toffee, molasses, nutmeg, clove. The birth of describing coffee by flavor profile instead of just by color.

Make sense? Great. Let’s get a little bit nerdier.

Understanding how temperature and time can impact the roasting process is one thing. Understanding how to manipulate them within the Coffee Development Timeline to produce exactly the flavors you want is something else entirely.

Sitting to one side of the roaster is Wade Reed, surrounded by a cluster of screens, dials, a keyboard, and–yes–a cup of coffee. He’s making sure this batch of beans moves through the stages of development according to a very specific plan.

On the screen in front of him is a graph with a curved line showing the times at which each stage should be hit, from start to finish. Also on the screen is a moving line, showing where the actual temperature of the beans is relative to the time they’ve been in the roaster. Wade’s sole purpose is to keep these lines matched up. Remember how your mom told you playing video games wasn’t going to help you in the real world? She was wrong. Nerd power.

Matt Kelly,

Early stage: When the green beans drop into the drum, they start equalizing with the heat around them at 160°. Then the heat is turned up. At 212° , a huge amount of water is pushed out of each bean as steam. But not all of it; some moisture remains trapped inside. Nothing much is really changing in the bean but the groundwork is being laid for successful development in the next few stages. The flavors being generated at this stage are called enzymatic aromatics; they’re floral and fruity, like citrus, berry and jasmine.

“These particular aromatics are very delicate,” Wade says. “They sort of want to break down and we have to fight to keep them around.” That might mean roasting a little quicker, terminating the roast sooner, or applying heat a little gentler.

Sugar-Browning: At 300° the sugars start breaking down. The trapped water acts as a thermal barrier that allows this to happen in a stable manner as things get hotter. At the same time, carbon dioxide is building up; the moisture protects the bean itself from breaking apart. The flavors produced at this stage are all sugar-based: caramely, chocolaty and nutty.

First Crack: Somewhere between 370° and 390° the bean pops. The remaining water finally gets pushed out and the surface cracks. Suddenly the bean becomes dry, delicate and far less stable.

“It’s really easy to scorch the beans at this point,” says Wade, eyes focused on the lines. “There can be an extremely rapid loss of the sweet flavors we’ve developed.”

Dry Distillation: Between 390° and 445° it’s time to stop applying heat and terminate the roast. But there are still flavors being developed. They tend to be more pungent and spicy like pepper, nutmeg and even tobacco.

“These aromatics can be a nice balance to the others we’ve already generated,” Wade says. “But they’re not typically the ones we want to dominate what you’re tasting.”

A broad generalization about roasting coffee is this: roasts that end at a lower temperature will have flavors that are more enzymatic, some that are sugar-based, but not many from dry distillation. As the end temperature gets hotter, the roast will have fewer enzymatic flavors, far more from sugar-browning, and dry distillation flavors that are more pronounced.

Second crack: Push past 445° and the bean pops a second time. Zero water is left. Carbon dioxide has built up so much that it completely ruptures the bean. The cellulose structure starts to break down. The oils in the bean rush out because there’s nothing holding them in any more.

“We really don’t like hitting second crack and damaging the beans,” says Wade, already dialing down the flames. “We’re bringing in some really beautiful coffees for people to drink.”

Cooling: During the roasting process, the beans start giving off their own heat. They will continue to roast themselves even after the external heat is shut off. The trick is to cool the beans as quickly as possible to halt any continued development that could push them past the desired flavors.

Wade pulls the lever and the beans spill into a wide-open bin below the drum. A mechanical arm slowly spins and spreads the beans. Fans blow directly on them.

Brown beans. Ready to grind and brew.

“These are our Mexican Oaxaca beans,” Ben says. Familiar beans that the staff at Joe Bean has been roasting for awhile. The development timeline for these beans is well known.

“But we just got in a new Rwandan Gishamwana coffee. We’re still experimenting to figure out the best roasting solution for these beans.”

It’s hard to know how a new coffee is going to react when roasted. Which means Ben and Wade need to do a whole lot of tasting to figure out what flavors can even be pulled out.

The Joe Bean team is currently roasting several new coffee varieties: Burundi Buhorwa, Colombia El Bado, Papua New Guinea Kunjin, and Rwanda Gishamwana. Four different beans, four different timelines, four different flavor profiles. Awesome.

Matt Kelly is a writer living in the Finger Lakes, slowly turning his home into a self-sufficient, food-independent, backwoods place of his own. He currently works with Fruition Seeds in Naples and Small World Food in Rochester. Which is why he drinks so much coffee. He writes regularly at

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