The process of roasting coffee is a fundamental step in the chain of events from farm to cup. It’s part science, and part art, and like any craft, it takes a lot of practice to perfect. Different roasters, and different machines, can produce wildly different flavors despite only really having control over 3 variables: time, temperature, and raw materials, the latter of which is externally dependent on the country of origin, farming method, etc. Every other feature of a roasted coffee is the result of deliberate decisions made by the roaster with regards to the time and temperature profiles.
In general, we can categorize the level of roast as light, medium and dark, although there are nearly an infinite number of sub-categories between them, and just as many combinations of profiles with which to reach them. The most prominent difference between these categories however, is the balance of acidity to bitterness, which have a reciprocal relationship.
Typically, the lighter roasts are known for their acidity and have been growing in popularity in recent years, possibly in conjunction with the increased demand for pour-over coffees. Light roasts offer better access to the inherent flavors of the coffee’s origin, giving the consumer less distractions from the natural aromas of the bean.
Darker roasts, often called French or Italian Roasts, are historically the kind of coffee you’d find in espresso, although there is a large following of medium roasts in espresso as well. It can even be a point of contention in places like Italy, where the Northerners prefer a medium roast, and Southerners like it burnt black. (In their defense, though, if bitterness is what you’re looking for, you can’t beat a cup of Neapolitan espresso!)
Roast also plays an important role in the body of the beverage, which is dependent on the level of oils extracted from the bean. Lighter roasts will be lighter in body (aka “mouthfeel”), as will the darkest Neapolitan roasts. For body-lovers like myself, we look for that roast just past medium where the body is at its peak.
Something that doesn’t change during roasting however, and this is commonly misunderstood, is caffeine. The chemical compound that makes up caffeine is not responsive to heat (at least at these temperatures), and therefore is unaffected by the roasting process. To repeat, light roasts and dark roasts have the same amount of caffeine.
In conclusion, roasting is a transformative process that utilizes the inherent chemical compositions of green coffee beans and reconfigures them into the 1000+ aromas we know and love in roasted coffee.
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