Most of us have a general idea of what type of coffee or roast we prefer to drink, but what impact does the roasting process really have on the flavor of our favorite coffees?
Flavor is not added during roasting.
It is important to note that the coffee seeds themselves hold all of the building blocks of flavor inside. During the roasting process, we develop these flavors by using heat as a catalyst for a wide range of chemical reactions. We do not add flavor to these coffees, but instead modulate inherent flavors through a roast profile.
The effects of time.
By controlling the energy input into the coffee, we can speed up or slow down the rate that the coffee is roasted. The is really comparable to different cooking methods (think quick searing vs. slow cooking in a Crockpot). One method of cooking is not necessarily better than the other, but the ingredients being used and our own preference might lead us to implement one style of cooking over the other. At least for that particular dish.
When we roast a coffee longer, we can bring out more perceived sweetness along with a heavier body. This will also mute perceived acidity in a coffee, yielding a sweet-forward cup without much brightness. If we wanted to maintain a high intensity of perceived acidity, we would roast the coffee shorter/faster to accentuate acidity. This faster profile may also have less perceived sweetness and a lighter body.
The take away: longer = sweeter and shorter = brighter.
The effects of temperature.
Along with extending roast time, we can also end the roast at a higher or lower temperature. As the internal temperature of a coffee bean increases, different chemical reactions begin and end. Acids are developed at lower temperatures than sugars, and so these acids will burn off or diminish at lower temperatures compared to sugars. As the roasting process continues, more and more compounds are “cooked off” eventually leaving the coffee void of any origin character and, in extremely dark roasts, breaking down the coffee into carbon which will eventually catch fire inside the roaster.
Most of our roast profiles at Avatar Coffee Roasters end between 400°F and 425°F.
During the chemical changes within the bean, the color of the coffee is also changing. As temperatures get higher, the coffee will darken in appearance. We use descriptions like “light” and “dark” to describe the color of the coffee and thus approximately describing the roast level.
Color is also the most straightforward way to measure roast level and track consistency. By measuring the color of each batch, we can create quality assurance protocols that flag batches outside of our accepted target. These marked batches can be sensorially evaluated in a blind tasting to check their consistency and uniformity with other batches that have either passed or failed a color quality assurance protocol.
The effect on volume and weight.
As coffee is roasted, the beans actually expand in size. Light roast beans can appear much smaller than dark roasted counterparts. Additionally, as coffee is roasted darker, the beans lose more and more weight. Light roasted beans might lose approximately 13 to 15% of their weight during roasting while dark roasted beans might lose up to 20% of their weight during roasting! The final roasted coffee has a much lower density than the green coffee before the roasting process.
Effect on caffeine during roasting.
A common misconception is that light, medium or dark roasts all have different levels of caffeine. This is not true. Caffeine does not begin to deteriorate until 460.4°F - As mentioned earlier, our roasts generally end between 400°F and 425°F, and most roasted coffee that you might find on the grocery store shelf is not roasted beyond 460°F meaning most roasted coffee does not reach the temperatures required to degrade caffeine in coffee.
Note that as beans are roasted darker, they expand in size while also losing weight. This means the method of dosing can cause variation in brewed caffeine between light and dark roasts... We will be discussing how caffeine content varies from up to cup in a future write up.
Modulating flavor in coffee through roasting.
In short, as roasters we can modulate the inherent flavors within a coffee by controlling time and temperature of the roast. These roast profiles are created based on constant tasting and refining.
Typically, our lighter roasts preserve the most origin character of a coffee and often have the brightest perceived acidity while our medium to darker roasts tend to have less origin character and more pronounced sweetness and body with a muted acidity.
Have any other questions? Get in touch with us and we would be happy to discuss in more detail!