Coffee Roasting Stages
Roasting coffee, at its core, is simply adding heat to coffee seeds. (Yes, I said seeds. Most people don’t realize that coffee “beans” are actually the seeds of the cherry of the coffee tree.) This heat transforms those seeds into a drinkable product. The roast process takes, typically, anywhere from nine to twelve minutes, depending how dark the roast profile is. The seeds will turn from a greenish color to some shade of brown. There are, however, very specific stages to the roasting process, and we will look at each one of those stages.
Specialty coffee will have anywhere from 10% to around 13% water content. As the roast goes along, the water within each seed vaporizes and exits the seed. If you’ve ever experimented with roasting coffee on your stove top or in a home roaster and your smoke alarm has gone off just a few minutes into the roast (it’s happened to me!), you can thank the water vapor! There is no smoke this early in the roast, but there is a significant amount of water vapor being generated.
The drying phase is over when all the coffee seeds have turned yellow, having lost all traces of green. Some call this marker, “dry end,” or, simply, “green to yellow.”
Next up is the Maillard Reaction. The Maillard Reaction is actually a group of chemical reactions and transformations that take place in the seed after dry end and before first crack. Maillard also coincides with the coffee seed starting to brown. The browning of the coffee is from the production of melanoidins. Melanoidins are made by the reduction of sugars and amino acids in the coffee seed.
The chemical reactions that are wrapped up in Maillard are responsible for some of the mouth-feel of the coffee, and for much of the complex, unique flavor.
The Maillard reaction concludes with “first crack.” Internal pressure has also been building during the Maillard phase. The pressure reaches a point where the cell walls of the seed break and a very audible popping sound occurs.
A significant amount of flavor development takes place from the end of first crack to whenever the roast is stopped. During this stage, the seeds are exothermic (giving off heat), whereas, up to this point the seeds have been behaving in an endothermic way (taking on heat). The post-crack development stage is where most of the aroma and flavor compounds are created. There is a fine line in this development stage for achieving peak flavor and body. If the coffee is roasted too lightly it may turn out too bright and acidic, but if that same coffee is roasted too long, all of the interesting flavor compounds will be roasted away and you’ll be left with more roast flavor rather than flavor that is unique to that specific coffee. If you pay attention to coffees sold in stores and shops, you’ll notice that single origin coffees are, much of the time, roasted to a lighter stage than blends. This is because the roaster is trying not to roast out the special traits of that single origin. This is why Clarity’s Ethiopia Guji is roasted lightly. If I were to take that coffee even a minute longer, the wonderful fruit notes would be roasted away and the coffee would be way less special.
Many of you have probably heard of coffees reaching a “second crack” during the roasting process. This is another audible crack that can be heard during roasting. Second crack is the wall of the seed breaking down further, becoming more porous as the coffee is continuing its roast. For now, I do not take any of our coffees to second crack because I do not want to over roast these special coffees. However, when we introduce other coffees, like a decaf, or an espresso blend, second crack will be necessary to achieve proper flavor.
There is much more to say on this topic, but I will leave it here for now. I hope this helps to understand the process. If you have any questions, please send me an email!