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The roasting process takes anywhere from 2 and 20 minutes, depending on the technology of the roasting machine used. The temperature is gradually raised during the roasting process, which has many different effects on the coffee beans. In brief, these are:
The light green coffee beans are thrown into the roasting machines, which have been preheated to 200 to 250 degrees Celsius.
  At 100° C the beans change colour from green to yellow. The water in the beans begins to evaporate. They first exude a grassy smell, and then one of boiled vegetables. |
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| At 120-130° C the beans turn chestnut brown and begins to smell like toast. |
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| At 130-140° C the beans appear speckled, freckled and wrinkled. |
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| At 150-160° C the coffee beans give off a smell of roasted grains. This scent signals that the coffee is about to reach its true aroma. |
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| At 180° C, due to the high temperature, the beans begin to release the vapours trapped within them and the coffee reveals its true aroma. The beans turn a cinnamon colour and begin to expand. |
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