We can develop flavour by roasting coffee,
Coffee beans are seeds matured in coffee cherry. They are then processed and dried to coffee beans. Before roasting, coffee beans are green in color and have a beany and grassy aroma. Actually, green coffee beans do not smell like coffee at all. When we roast coffee, we develop 800 to 1000 different aroma compounds. These compounds make the flavour of the coffee.
In the beginning of development stage the reaction becomes exothermic and the coffee cracks. During drying and browning stages the bean has collected energy that makes the coffee to explode. Development time is when the wanted aroma compounds are developing. If we do not slow down the roast at development stage, we easily get coffee that is smoky tasting and the flavour is too sharp.
Typically light roasted coffee is more acidic, and dark roasted coffee is more bitter. Also fruity flavours are more common on light roasts, and roasty and burnt flavours are more common on dark roasted coffee.
Even though roast degree has the biggest role on coffee’s flavour profile, total roast time and time of each stage are also important factors. If you roast fast, you will get more desired aroma compounds. But be careful not to burn the beans! Coffee’s total flavour (fruity, berry-like, chocolatey, nutty altogether) is stronger. Also the amount of aroma compounds, which are created in the beginning of development stage, is higher with fast roasting.