Roasting coffee turns a green flavourless seed into a brown aromatic bean. It typically takes between 7 and 20 minutes. The roasting can be stopped when the bean is a light colour or left to develop a very dark brown but the same colour can be achieved with a fast, hotter roast or a slow cooler roast. The longer a coffee is roasted, the less acidity it will have but the more bitterness. Sweetness is at it’s peak somewhere in between.
A good roaster will shape the character of the bean to highlight desirable traits such as peach-like acidity in Ethiopian Yirgacheffe or chocolate notes in Brazilian Daterra. They may also be able to mask some undesirable traits but it’s less of a science and more of an art.
If you see a strength rating on a packet of coffee beans it refers to how darkly the beans have been roasted not how strong the coffee will taste. Coffee strength comes from the quantity of coffee you use. You can see the rating as a measure of how bitter the coffee will taste as darker roasting brings out more bitterness.
Once the coffee has been roasted the clock starts ticking for it to be enjoyed at its best. Over the first few days the beans will degas which is actually a good thing as the flavour will settle. After 7 to 9 days oxidisation kicks in and the flavour will decline. It’s so important to get freshly roasted beans and enjoy them at their best. The best way to store them is in an air-tight container away from light. The fridge or freezer are damp places so not good for coffee. Ground coffee looses its vibrant flavour within 90 seconds for finely ground and 20 minutes for coarser grinds so store coffee as whole beans and grind just before brewing.