One way to look at cooking and food preparation is to see it as applied chemistry. The same applies to the coffee drink every morning. The coffee that we drink starts out as a “green” coffee bean that has a distinct grassy taste if brew it up. The aroma and flavor that we are accustomed to are the result of roasting green coffee beans. We generally think of this process as resulting in a range of aromas and flavors depending on time spent roasting and roasting temperature but there are also a host of chemical changes going on when coffee beans are heated up into the 400 degree Fahrenheit range. Here are some thoughts about the chemistry of coffee roasting.
Chemical Reactions When Roasting Coffee
Coffee roasting has been extensively studied and the various stages given names. They are the Maillard reaction, caramelization, Strecker degradation and pyrolysis. Each one contributes to the aromas and flavors we associate with our coffee.
Maillard Reaction
When coffee being roasted reaches the 300 degree Fahrenheit range coffee being roasted turns a light brownish gold similar to what happens with meats and baked goods and starts to develop a rich flavor and aroma. This process was described by a French chemist more than a century ago.
Caramelization
As the temperature of the roasting coffee climbs above 320 degrees Fahrenheit sugars in the coffee begin to break down resulting in nutty and sweet flavors. The caramel-like flavor in darker roasts comes specifically from this process.
Strecker Degradation
As coffee roasting temperature rises a bit higher, alpha amino acids in coffee are converted to imines which in turn are broken down into aldehydes and carbon dioxide via hydrolyzation, providing even richer and more varied coffee flavors. This process is common in baking various foods as well as in the roasting of coffee.
Pyrolysis
The next and last chemical process in coffee roasting occurs as temperatures go up and as time spent roasting proceeds. This process gives dark roasted coffee its darker color, reduced acidity, and heavier “body.” It is at this step that more complex chemicals are broken down. This step leads the loss of chemicals responsible for the “brighter” taste of a more lightly roasted coffee.
Understanding Coffee Chemistry When Roasting
Coffee roasting should not be a blind process. The first chemical step, the Maillard reaction, gives coffee its brown color and start the process of adding unique flavors. Aroma of roasted coffee largely comes from Strecker degradation. Sweet and caramel like flavor comes from caramelization and the “roasted” flavor and darker color happen with pyrolysis at the highest roasting temperatures and longest roasting duration.
You Do Not Have to Memorize the Chemical Steps of Coffee Roasting!
Coffee roasting should not be a laborious or tedious process. Once you find the best roasting process for the coffee that you like, simply follow the same steps every time you roast and enjoy your coffee. The chemistry will take care of itself so long as you repeat the exact same process each time.