There are three main characteristics that contribute to the overall flavour profile of a coffee: acidity, sweetness and bitterness. In a well-balanced coffee these three qualities work together, not masking or competing with each other, producing the “story” of the coffee for the drinker; for example, a coffee may begin with a fruity plum acidity, supported by a bittersweet chocolate and completed by a sugar-toasted nut finish.
This is a positive attribute of coffee, giving depth and nuance to the flavour and often considered the primary marker of higher-quality coffee. It is the bright, dry sparkling sensation that gives the coffee life on the tongue, similar to that experienced when drinking red wine. Acidity is responsible for the fruit notes in a coffee which can exhibit as citrus (lemon, orange, grapefruit), stone fruit (cherry, plum, apricot, peach), berry (blackberry, strawberry, raspberry) or sometimes a hint of crisp apple or fresh melon.
Sweet flavours such as brown sugar, caramel, molasses, honey or butterscotch provide a counterpoint to the acidity and round off the coffee. This can also be experienced as a nutty or toasted flavour.
Bitterness can be a negative thing, but when in harmony with acidity and sweetness it can make the difference between an average coffee and a great coffee. It plays a particularly important role to complete the profile in an espresso.
The roast of a coffee (whether light, medium or dark) has a significant impact on the final flavour profile of the coffee. Generally speaking, a light roast will have more acidity, while roasting the beans for longer brings out more of the sweetness.