All coffee guides · Roasting
Roast level is one of the most visible pieces of information on a coffee bag, and one of the most misunderstood. Light does not mean weak. Dark does not mean strong. Roast level describes how far the roasting process was taken, and it has a profound effect on what ends up in your cup — but perhaps not in the way the supermarket colour scale suggests.
Roasting transforms a green, grassy-smelling seed into the aromatic, complex bean we recognise as coffee. Heat drives hundreds of chemical reactions: sugars caramelise and then burn, amino acids react with sugars in the Maillard reaction to create hundreds of new aromatic compounds, acids develop and then break down, and water and CO2 are driven out as the bean expands. The roaster controls temperature and time to stop these reactions at a point that achieves the desired character. Stop early: origin character preserved, high acidity, lighter colour. Go further: more sweetness and body, then eventually more bitterness, darker colour, oils on the surface.
Light roasts are stopped shortly after first crack — the exothermic event when the bean expands and pops. The bean retains most of its original character: the acidity is higher, the flavour is more complex and origin-driven, and the colour is light brown with no surface oils. Light-roasted specialty coffees from Ethiopia or Kenya can taste floral, fruity and tea-like in a way that seems surprising if you are used to darker roasts. They are not weak — a light-roasted espresso can be intensely flavourful — but they require more careful brewing because the extraction window is narrower.
Medium roasts develop further past first crack, into the "development phase" where the Maillard reactions have more time to build sweetness and body. Acidity softens, chocolate and caramel notes emerge, and body increases. The balance between brightness and richness is at its best here for many coffees, particularly Latin American origins like Colombia and Brazil. Most specialty espresso roasts land in the medium range. Surface oils are still minimal, and the bean has a medium-brown colour.
Dark roasts go further still — often into or past second crack, where the cell structure begins to break down and surface oils appear. At this stage, origin character is largely masked by roast character: the earthy, bitter, smoky notes you taste are primarily products of roasting rather than the coffee's origin. Body is heavy, acidity is very low, and bitterness is the dominant sensation. Many people prefer this style in milk-based drinks where the coffee needs to push through. At its best, dark roast can be rich and complex; at its worst, it tastes harsh and ashy.
There is no industry standard that defines where "light" ends and "medium" begins. One roaster's medium is another's dark. This is why reading the description and tasting notes on the bag matters more than the label. A bag that says "medium roast, notes of dark chocolate, low acidity" is telling you more than a bag that just says "medium." In specialty coffee, roasters tend to roast lighter than commercial brands, so if you are coming from supermarket coffee, a specialty "medium" may taste lighter than you expect.
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