The roasting process is one of the final steps in the long journey that coffee takes from the farm to your cup. The art of roasting coffee takes years to learn and master and is one of the biggest factors contributing to the overall flavor and pleasantness of your cup. Under the skill of a Master Roaster, a coffee has the opportunity to showcase what makes it unique; its sweetness, acidity, body, flavor and aroma. Without proper care and attention, a coffee that might otherwise be vibrant and extraordinary will become flat and uninspired. The roaster’s responsibility is to take their understanding of the science of roasting and elevate it to an art form, developing coffees to their greatest potential. So, what is coffee roasting?
What is Coffee Roasting?
Simply put, coffee roasting is the controlled application of heat to coffee beans over time. During the roasting process, coffee is taken from room temperature to somewhere between 400 – 430 degrees Fahrenheit. The art of roasting is determining how to get the coffee to that temperature, and how long it should take. This decision is called a profile, and each of our coffees has a unique one. A coffee’s origin, processing, altitude, moisture content, and many other factors - as well as whether it’s being used for espresso or drip brew - will all contribute to how a roaster decides to profile it.
Needless to say, coffee roasting is a very complex process. The simplest way to understand it is to break it down into parts. (Note: this is by no means a comprehensive exploration of roasting. Rather, this should act as a general overview of the process).
While it may not seem like it at first, the color change that a coffee exhibits throughout the roasting process is one of the primary cues a roaster will use. In fact, as consumers we use color (light, medium, and dark roast) to set our expectations of a coffee.
Prior to roasting, coffee generally has a light green color (though different coffees often have different shades of green). Unsurprisingly, coffee at this stage is referred to as…Green Coffee. Shortly after the coffee is put into the roaster, it starts to change color, going from green to yellow to tan, and eventually to dark brown. The primary driver of this color change is the Maillard reaction, which is a reaction between amino acids and reducing sugars in the coffee. This reaction is responsible for most of the browning you see in foods – steak, bread, french fries, and toasted marshmallows, for example. Roasters will use these color changes to know how quickly (or slowly) the coffee is roasting, and to know when to remove the coffee from the roasting machine.
Physical Structure Changes
In addition to color changes, the coffee bean itself goes through many structural changes. Due to the intense (albeit controlled) application of heat, coffee loses most of its moisture content, leading to about a 15% reduction in mass. This means that if you start a roast with 50lbs of coffee, you’ll usually get about 43lbs out! Additionally, the volume of each coffee will significantly increase, usually doubling in size. Both of these characteristics have to do with how coffee reacts to the heat surrounding it.
At the beginning of a roast, coffee is endothermic, meaning it absorbs heat. Once the coffee gets to an internal temperature of about 400 degrees Fahrenheit, it becomes exothermic, giving off heat instead. At this stage the coffee will make audible popping sounds, an event colloquially called “first crack”. This process is similar to how popcorn react to heat: absorbing as much as it can until – POP – it explodes! While not nearly as dramatic as corn kernels, first crack is (more or less) the same reaction.
While only lasting for 30 – 45 seconds, first crack is a big moment during the roasting process, because it’s after this point that coffee flavors, aromas, body, and acidity really start to develop.
Flavor, Sweetness, and Acidity
Of course, the ultimate goal of the roasting process is to cultivate the final flavors and aromas we’ll experience in the cup. And while each coffee has its own unique flavors (like jasmine, blueberries, butterscotch, etc…), every coffee develops those flavors in a very similar way.
Sweetness in coffee develops as a product of the sugars and carbohydrates in coffee. The coffee bean is actually the seed of a coffee cherry, which imparts a lot of its sugars (polysaccharides) into the bean. As you would expect, different beans have different amounts of sugars, which is why some coffees are naturally sweeter than others. These sugars break down during the roasting process, contributing to caramel and fruity aromas (as well as the Maillard reaction).
Another big component of a coffee’s flavor is its acidity. When we talk about acidity in coffee, we’re talking about perceived acidity (bright, effervescent, sparkling flavors), and not the actual pH level. Acids occur naturally in coffee, and each can provide an array of flavors that you likely have tasted in other foods.
Coffees are their most acidic right after first crack, and become less acidic the longer the roasting process goes on.
Coffee aromas are the result of the development of volatile aromatic compounds inside the beans. Volatile aromatics evaporate at low temperatures and become trapped inside unground coffee. This is why a coffee’s aroma is the most intense right after grinding, and also why we recommend not pre-grinding your coffee! There are over 800 volatile aromatic compounds in coffee (for perspective, wine has roughly 200) which appear in varying concentrations in coffee. These compounds peak in development shortly after first crack, after which they slowly dissipate.
Light vs. Dark Roast
On one extreme end, very light roasted coffees are considered underdeveloped, which is characterized by high acidity, having a light body, and grassy, overpowering flavors. On the other end, very dark roasted coffees are considered overdeveloped, characterized by a lack of sweetness and acidity, burnt and bitter notes, and a lack of distinguishing flavors. The roasting process itself begins to impart “roasty” flavors after first crack, which at their onset are very pleasant, but become unpalatable the longer the coffee is roasted. This is similar to grilling steak; the rarer the steak is, the more intensely you can taste the meat, and the more well done a steak is, the more it tastes like the grill. And just like with steak, the art of roasting is about finding the balance between those two extremes.
Our philosophy on roasting guides our hands, as we roast coffee to focus on the classic characteristic flavors unique to each country to bring out the depth and complexity they have to offer. Ultimately, our roaster’s responsibility is to find the perfect profile for each coffee; the profile that highlights what makes each coffee unique, and creates a pleasant balance between its sweetness, flavors, and acidity. It’s their responsibility to take the science, physics, and chemistry of the highly complex coffee roasting process, and make it art.
For example, our Casetta Blend is a combination of three coffees from Costa Rica, Guatemala, and Ethiopia. Each coffee in that blend has it's own unique profile, to bring out what makes it special. And, since Casetta Blend is intended to be a drip coffee, we roasted it on the lighter side of medium and created a perfect balance of flavor. The care, craftsmanship, and knowledge of our roasters shines through in this blend, demonstrating an appreciation and understanding of the roasting process.