Roasting takes a hard, tasteless, green seed and turns it into the aromatic bean we know and love. There are several kinds of machines used to roast coffee, but the most common is the drum roaster, a rotating drum over an open flame fueled by natural gas, controlled by an experienced hand. The process takes somewhere around 10 or 12 minutes.
We like to break it up into three parts.
When the coffee is introduced into the roaster, the drum is already preheated, so we watch the beans cool down the roaster as they start to take on some of that heat. As the newly full drum reaches a sort of equilibrium, the master roaster will really apply the heat to get the coffee cooking. This beginning is called the dry phase. Much of what happens in the dry phase is moisture evaporating, the coffee drying. We don’t see any physical changes for several minutes.
The first visual change is yellowing. This is how we mark the end of the first phase and the beginning of the second. During this second phase, the coffee begins to give off an aroma like baking bread. A thin, papery layer falls off, while the machine separates and stores that chaff. During these first two stages, the master roaster takes enormous care not to go too fast or two slow, either way could result in negative effects on the coffee.
The second phase ends with a bang. Or a crack rather. This is where all the fun happens. We start to see browning caused by the maillard reaction and hear a crack caused by gas pressure inside the bean. When this crack happens, the beans pop like popcorn and get a little bigger. This is when the master roaster starts to watch very closely. We’re just a minute or two away from a finished product.
When the coffee is just right, the roaster will pour the contents of the roasting drum onto a cooling tray and use air to quench the coffee (rapidly bring the temperature down), ending the process and cooling the beans for storage.
Many roasters will put the time in the cooling tray to good use by doing a visual quality check on the coffee. They commonly find foreign debris like small stones from the farm or beans that just didn't roast consistently. These are picked out by hand.
The next day, the coffee goes through one last quality check as the roaster or quality control team will taste the coffees, scoring them according to their own company standards.
There could be a fourth phase if you’re looking for a dark roast. You won’t usually find this at Clarity, but it has it’s place in the industry. When roasting very dark, there is a second crack. This causes oils to rise to the surface, giving the beans a shiny look.
Most specialty coffee professionals will suggest keeping your freshly roasted coffee for only a couple of weeks. As the roasted coffee ages, it begins to oxidize and the flavor becomes stale. One way that we can battle this oxidation is by using sealed bags with a one-way valve. This valve allows carbon dioxide to escape the roasted coffee without allowing oxygen inside.
While unroasted coffee doesn’t go bad for years, per se, the flavors can become muted and bland, so we don’t often see roasters keep the same coffee on their menu for more than a few months at a time. We don’t mind that so much because it means we always have new exciting things to try!
Check out the section on Brewing to learn how to turn this freshly roasted coffee into a delicious pour over.