Green coffee beans have little flavor. Applying heat to the green beans, however, releases the hundreds of flavor compounds hidden within them. These sugars, oils, proteins, and minerals develop and change composition as a result of roasting.

Depending on how well the roasting process is controlled these chemical changes will ultimately result in desirable - or undesirable flavors. To further complicate the process, each coffee reacts differently during roasting, depending on its country of origin, the environmental conditions under which it was grown and harvested, and the method of processing used.

As a result of these various factors, roasting each coffee to its peak color and flavor is truly an art. The coffee roaster must keep a careful eye on the temperature and time of each batch of beans.

Before being placed in the roaster, bags of green coffee are usually emptied first into cleaning equipment to remove any stones, sticks or dust that may be mixed in. As they are subjected to the heat of the roasting equipment, the beans progressively lose moisture and the sugars in the beans begin to caramelize. At 212° F the beans turn pale yellow; at 302° F they swell, doubling in size. When the beans’ temperature reaches approximately 400° F series of chemical reactions rapidly occurs.

These changes known as “Pyrolsis,” alter the chemical composition of the beans by releasing substances that characterize coffee’s aroma and taste. Pyrolsis produces a “crack”sound, as the bean fibers break open and expand because of the heat. Darker roast coffees, in which oils seep to the bean’s surface to produce a shiny look, often have a second “crack” sound.

The roasting process also releases any silver skin remaining on the bean. This by-product known as chaff is usually drawn off and disposed of.

When beans reach the desired roast color, they are quickly cooled; otherwise they will retain heat and continue to roast.