Roasting is one of the most fascinating aspects of the coffee industry. It takes the green coffee seed, which has almost no flavour beyond a quite unpleasant vegetal taste, and transforms it into and incredibly aromatic, astonishingly complex coffee bean. The smell of freshly roasted coffee is evocative, intoxicating and all-round delicious.
Specialty roasters around the world are, by and large, self trained and many have learned their trade through careful trial and error. Each roasting company has its own style and aesthetic, or roast philosophy. They may well understand how to replicate what they enjoy drinking.
Fast ot slow, light or dark?
To simplify matters, it can be said that the roast of a coffee is a product of the final colour of the coffee bean (light or dark), and the time it took to get to that colour (fast or slow). To simply describe a coffee as a light roast is not enough, as the roast could have been relatively fast or it could have been quite slow. The flavour could be quite different between the fast and the slow, even though the bean may look the same. A whole host of different chemical reactions occur during roasting, and several of them reduce the weight of the coffee, not least of course the evaporation of moisture. Slow roasting (14-20) minutes will result in a greater loss of weight (about 16-18 per cent) than faster roasting, which can be achieved in as little as 90 seconds. Slow roasting will also achieve a better, if more expensive cup of coffee.
The roasting process can be controlled to determine three key aspects of how the coffee will taste: acidity, sweetness and bitterness. It is generally agreed that the longer the coffee is roasted, the less acidity it will have in the end. Conversely, bitterness will slowly increase the longer the coffee is roasted, and will definitely increase the darker a coffee is roasted.
Sweetness is presented as a bell curve, peaking in between the highs of acidity and bitterness. A good roaster can manipulate where may be sweetest in relation to its roast degree, producing either a very sweet, yet also quite acidic coffee, or a very sweet, but more muted cup by using a different roast profile. However, adjusting a roast profile can never improve a poor-quality coffee.