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Home :: Roasting :: The Roasting Process
Chris at Work
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Coffee Roasting
See Coffee Roasting Video
Roasting coffee is simply the addition of heat and air to the bean over time. The amount of heat and air and the point and method in which they are introduced can alter the flavor of the coffee dramatically, so while a computerized machine can be programmed to roast coffee, a good artisan roaster does it by hand, making changes to the controls based on the development of the beans in order to achieve the same results batch after batch.
The process begins by heating the drum for half an hour and normalizing the air flow through the duct work. When the drum has reached the right temperature, the beans are dropped into the drum, called 'charging the drum.' Charging begins the process of transferring thermal energy from the roasting drum to the beans.
Unroasted green beans, ready for roasting... |
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Chris loading the next batch into the hopper. |
As the coffee begins to take on heat, the moisture in the bean turns to steam, heating it from the inside. At this early stage in the roast, in the roast the coffee ever so slightly begins to yellow, and smells like fresh-cut hay.
Yellow-Green - 265° - 4min50sec
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Mustard - 300° - 6min40sec |
As the roast progresses, the color of the bean begins to change from yellow green to mustard yellow as the moisture begins to dry out.
The smell becomes increasingly sweet due to the rapid caramelization of the coffee's sugars, and the color changes from yellow to cinnamon. During this stage, the bean swells, causing it to shed the thin coating known as the 'chaff.'
Cinnamon - 344° - 8min40sec |
Shortly after the 'cinnamon' stage the coffee pops audibly like popcorn. This moment is called 'first crack', and during first crack, the bean doubles in size, the wrinkles on the surface smooth out, and the color changes to light brown.
The popping ceases and the bean begins to color darker and darker mahogany until it pops a second time ('second crack'). At this point, the chemical and color changes in the bean happen so fast that the roaster needs to see and smell the coffee constantly to make sure that it is not being overcooked.
First Crack - 388° - 11min22sec |
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Second Crack - 440° - 14min30sec |
While each roaster has personal criteria for doneness, as a general rule, the longer the roast, the more the body increases and the acidity decreases. On our small batch roaster, a full-batch roast takes between 14 and 16 minutes depending on the hardness of the bean, the desired final roast depth, and flavor profile the roaster is seeking. Metropolis roasts to many different levels, depending on the individual characteristics of the bean or of the roast.
When the roast is complete, the beans are dropped into a cooling tray with a moving arm called an agitator. The air flow is directed onto the beans, cooling them to room temperature in about three minutes.
My dad, Jeff Dreyfuss, dropping a batch of Italian Roast for Chicago Tribune Photographer Bob Fila |
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A batch of beans cooling in the tray |
Chris Schooley is a prolific and well published writer on the subject of coffee roasting. Please follow these links to read some of his articles.
Fresh Cup, 2004
The coffee is now ready to move into production
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