Coffee roasting turns raw green beans into varying shades of brown and black. The flavour of good coffee is, to a great extent, influenced by two factors: the degree of roast and the methods or style of roasting.
Basically, there are four degrees or grades of roasting: Brown Roast, Dark Brown Roast, Medium Dark Roast and Black Roasts, each of which produces a distinctive taste, aroma and character.
Natural sugars within the coffee beans are developed at this stage after about 14 minutes of roasting, just before the ‘second crack’ and the character unique to each individual variety and origin is revealed. When delicate fragrant, floral or citrus notes exist in some fine rare coffees, they may be present only at this point. Of course this means that any minor flaws, if present a bean, may be detectible in a Brown Roast but would mellow out with a little more fire. Brown roasted coffee beans have a dry smooth surface and produce a brew with balance of sweetness and brightness.
Our brown roasts
After 15 minutes, when the coffee beans in the roaster reach a high enough temperature, the cell walls of the beans begin to rupture and give off gas (mostly CO2). Natural sugars start to caramelise becoming more flavourful and slightly less sweet. Small shivers explode off the surface of occasional beans making ‘rice crisp’ sounds and leaving a miniature dark crater or a speck of oil. From the time this starts until it sounds like your breakfast cereal, the character of Medium Roast is created; smooth, full, caramel. Excellent for any brewing method, this is the roast for straight espresso, Northern Style, lively but not sour, sweet and spicy, strong but not bitter.
As coffee keeps roasting it progresses to a ‘rolling’ second crack accompanied by staccato crackling static. Natural sugars in the coffee beans continue to caramelize to toffee, acids are muted, and specs of oil appear on many beans. Dark coffee has a more complex flavour, dark chocolate notes, and a hint of bitterness. At this degree of roast, most of the individual characteristics of the original beans are lost, and new flavours are imbued by the roasting process. Southern Style espresso made from a dark roast is intense, chocolate, and powerful enough to make great cappuccino and café latte. It takes approximately 16 minutes to bring coffee to the dark side.
The roastmaster’s skill plays a more important role than the type of bean in this particular roast but it takes a bean with some exceptional or assertive character which, even after being subjected to the abuse of the fire, to give a distinctive and recognizable cup. By continuing the roasting process and slowing down the air flow, the oils in the coffee beans released by the second crack come to the surface and produce aromatic smoke as they hit the hot roasting drum. Best prepared by press, filter, or vac pot, Black Roast coffees are very dark with a slightly oily surface. They are lower in acid than the other roasts and have a bittersweet-smoky flavour sought by coffee aficionados.