Most coffee lovers don’t consider the science involved in the taste of their first or last cup of coffee of the day. There are complex chemical processes, and specific actions that roasters must take, to extract the flavor without “burning” the bean. What we taste is the result. It is the roasted coffee bean we grind and then brew, mostly without thinking of what happened to it before, that makes your mug of joe taste uniquely delicious.
Some may think of “roasting” as only heating the beans before grinding. However, it takes a mix of precise science and artistry to unlock the flavorful potential of your favorite roast. Here’s a quick explanation of what goes on during the process.
First, the coffee roasting equipment must reach a stable temperature before the beans are added. The beans dry out as they are exposed to the heat, and the energy of the heat causes the beans’ chemical compounds to break down, react, and create new compounds altogether. As the heat rises inside the seed, the chlorophyll (which gives the beans their color) breaks down, and the bean begins to yellow, sometimes even turning to a grayish color.
At a certain point, the internal temperature of the bean causes something called the Maillard Reaction to take place, which is where most of the flavor of the coffee develops. The reaction takes place between the amino acids and sugars of the beans, causing them to turn brown, give off the coffee aroma, and form volatile compounds that will change throughout the roasting process. Caramelization also occurs at this stage, darkening the bean and adding a level of sweetness and complexity to the coffee’s flavor.
Most coffee lovers don’t consider the science involved in the taste of their first or last cup of coffee of the day.
Shortly after the Maillard Reaction occurs, you’ll hear a sharp crack coming from the beans. This noise happens just shy of 400°F (or just below 200°C) when the water vapor inside the seed has expanded so much that the surface splits to let out that water and oxygen. As a result, the beans become more porous and brittle; the time immediately following the first crack has the most significant impact on the ultimate flavor of the coffee.
Variables and Variance
Depending on the type of bean and the type of roasting, the next step can vary significantly. Roasters monitor the temperature and time passing after the first crack and usually experiment with different variations of these factors to see which combination produces the most flavorful roast. Among the various aspects that can be changed depending on the time and temp at this step are acidity, sweetness vs. bitterness, and aroma of the coffee. It’s also worth mentioning how carefully roasters need to track these variables. A second or two difference, or a few degrees variance, can make two roasts of the same beans taste very different. Most customers, when they find the roasts that they prefer, want the flavor to be consistent.
A delicious cup of coffee requires thoughtful and scientific precision.
For lighter roasts, this is where the cooling step begins, but for darker roasts, there is a second wave of cracks from the beans. This time, it’s not water and oxygen being released, but carbon dioxide and oils as the beans’ cellulose breaks down, and it actually sounds less like a crack and more like a sizzle. Roasters must stop the process soon after this happens since the beans heat to such a point that they will quickly catch fire.
Whether the roaster has brought the beans to a light roast and taken them out, or let them go on to a dark one, they will need to be rapidly cooled down so that the many chemical reactions taking place inside will halt. Just like cooking meat, when you take it off the grill or pan, the internal temperature will still be high enough for it to cook inside for a little while. But this isn’t ideal for coffee beans, where precision and timing are crucial; they need cooling fast. Air cooling can bring them down closer to room temperature quickly and get them out of the cooking range.
A delicious cup of coffee requires thoughtful and scientific precision. At South Slope Coffee, we do extensive experimentation with each lot of every coffee to find its best profile. It’s this tedious dedication to optimal roast that results in the perfect taste. If you want to experience the results of our careful roasting experimentations, iterated to perfection, visit our shop here and consider a subscription bundle to get more flavor for your dollar.