Light roast, medium roast, dark roast; when it comes to coffee, you can certainly hear plenty of opinions about how to best roast the beans. Yet the process of roasting is more complicated than throwing the beans in an oven for a day or two, a reflection of the meticulous nature of coffee producers and baristas who have elevated this drink to an art form. Coffee roasting is the first step towards making a great cup of joe, but not all roasts are created equal, and the beans you grind and steep can go through many pathways before they wake you up in the morning.
You may have seen enough coffee beans in a bag or a grinder to think that they are like black beans or pinto beans, growing beneath the ground, but coffee is not a bean. It is a fruit, one that bears a resemblance to cherries: they start out as green buds that grow larger and become red when ripe. This is why the fruit itself is called a coffee cherry. Eating one coffee cherry won’t give you much of a buzz, although legend holds that an Ethiopian goat herder found his flock more energetic after consuming some of these strange fruits.
Unlike modern cherries that have been grown to be big, juicy, and have lots of tasty flesh, coffee cherries are just a bit of fruit grown around a large, central seed. We throw away the seeds of cherries (and peaches and apples and even bananas), but the seeds of coffee are the black gold we all cherish.
The 3 Stages On Roasting A Coffee Beans
1. Drying Stage
The first step in the process is to remove skin and flesh from coffee cherries until only the seeds remain. These greenish-yellowish pods are the reason why you’re never more than a few blocks away from a Starbucks.
After taking apart everything but the seed, coffee is dried (usually in the sun) to eliminate all extra moisture remaining. Once dry, you might be forgiven for mistaking them for something like a pumpkin or sunflower seed: they have a beige coloration and smell more like grass than the java we all know and love. The change in appearance, taste, and drinkability depends on the roast profile, which in turn depends on the roasting stages.
The roasting process turns the coffee beans from raw, greenish, and squishy into the hard, dark, cooked beans that are the final product. The first step is the drying stage. Didn’t we just say that beans are dried after harvesting? Yes, but drying beans in the sun is different from the drying stage of the roast, when beans (with a humidity level of about 10%) are added into a drum roaster with a temperature of 320 degrees. This sounds hot to us, enough to cook a freezer pizza, but it’s not much in the grand scheme of the roasting process, and coffee producers must be careful not to burn the beans. The drying stage lasts just five to ten minutes before the beans are ready for the next leg of the roasting journey.
2. Browning Stage
As you can guess, the coffee beans change color here, but also smell, taking on a hay-like aroma. Coffee beans in the browning stage are subject to a chemical change known as a Maillard Reaction, when heat affects the sugars within a substance, the same change that occurs when bread dough turns into thicker crust. Its in this stage that coffee gets its signature aroma and taste: like many other mass-produced beverages, including wine and tea, coffee developers extract aromatic chemical compounds with very long names like acetaldehyde and 3-methl-2-buten-1-thiol from the beans during the browning. These compounds add flavors that range from smoke to caramel, resulting in a complex array of tastes and scents.
The duration is usually just ten to fifteen minutes, as the time spent in the browning stage will influence the type of roast; a dark roast spends more time in the browning stage than a light roast. No matter the duration, this is the point where coffee beans begin to crack, opening a fissure in their outer skin. For a dark roast like an espresso, the coffee beans are allowed to crack twice before they are yanked out of the roaster.
3. Development Stage or Roast Stage
The last stage is the development stage, or the roast stage, where the temperature is reduced and the beans are allowed to release some heat. This prevents them from exploding, while also keeping them from getting too tangy or sharp of a taste profile. This stage is quite short, usually only a few minutes, and is determined by the roaster’s own desires: for a fruitier taste, a shorter roast stage is needed.
Coffee roasting can, and often is, something that can be done at home. Some people use nothing more than a baking sheet and an oven, while a bigger café that sells hundreds of cups per hour will use a larger roasting drum with more sensitive instruments to measure temperature and humidity. A fluidized roaster, for instance, will use hot air rather than direct heat, reducing the risk of burning and enhancing the flavors. Homebrewers should carefully monitor both temperature and time to avoid overcooking their beans. Experiment with the duration and intensity of the roast to see how well you enjoy a particular variant of roasted coffee beans.