Let’s get cracking on today’s coffee lesson. Today we’ll dive into the chemical process that transforms those green beans into the aromatic, brown beans we’re all familiar with. The process is so complex, it’s not fully understood, but what we do know, we’ll share with you on this episode of Coffee On The Brain.
Roasting coffee beans produce over 800 aroma and flavor compounds. There are two chemical component groups, volatile and nonvolatile, that occur during the roasting process. The volatile components create the aroma while the nonvolatile create the basic flavors that we get from coffee such as bitterness or sourness. Caffeine falls into the nonvolatile category and accounts for some of the bitterness in your cup.
Now to the good stuff: the roasting stages. Each stage goes through a number of endothermic and exothermic phases. To sum it up, the endothermic phase is when the beans absorb the energy in the form of heat whereas the exothermic phase the beans release the energy. It’s easy to remember “en” as “in” and “ex” as “exit,” for those of you taking notes.
Try roasting coffee beans right in your own home. We’ve got the Behmor 1600 Plus Home Coffee Roaster and Velton’s Bonsai Green Beans - Unroasted to create the right roast for you. You'll have the freshest coffee on the block and a perfect conversation starter during your next brunch out. Check out this video we’ve made with the Behmor roaster and give it a try!
Roasting Stages
Stage One: Endothermic
The green beans absorb energy in the form of heat, lose moisture and mass and begin to turn yellow in color. Beans will give off a toast or popcorn smell.
Stage Two: First Crack
Heat released in the form of steam creates a large crack during the exothermic phase. The beans double in size and turn light brown.
Stage Three: Pyrolysis
Fats and sugars in the beans continue to break down and develop the aromas and flavors we know and love. Roaster's typically stop roasting during this stage.
Stage Four: Second Crack
Pressure formed by various gasses crack the beans again. The beans deepen to a medium to dark brown and begin to develop a sheen as oils are pushed to the surface.
Stage Five: Final Roast
Most roasters will stop prior to the second crack to retain the bean's flavor. The longer the beans are roasted, the less unique flavored is preserved.
