Updated: Apr 10, 2018
We regularly hear people speaking about light, medium and dark roasted coffee. This article will cover what is meant by these terms without going into the science of roasting.
As coffee is roasted it changes from a hard, grassy-scented seed into a fragrant, brown, gorgeous-smelling bean. During roasting the colour will change, going into a yellow tinge that becomes browner as the sugars caramelise. Beyond this point, oils begin to surface on the bean as it blackens. The water content within the bean drops and the longer they are roasted the more they expand, eventually combusting. The picture below shows this development.
Roast colour is measured on the Agtron scale. This is a piece of equipment that uses infrared light to read the colour of a bean, not its chemistry. It’s therefore important to remember that a darker bean doesn’t always necessarily mean a darker roast. Some beans are duller in colour at the green stage, or may
already be yellow, such as the Monsoon Malabar coffees from south-west India. Although two different coffees may have the same colour, they will most likely not taste the same.
To the right is a rough guideline to roast colour and corresponding number on the Agtron Scale.
So what is a light roasted coffee?
A light roasted specialty coffee will have more of the coffee’s natural flavours (fruits, vegetable, floral), have higher acidity and a more muted bitterness. There will be no visible oil on the surface of the bean and in most cases it is light brown in colour.
A dark roast exhibits more roast flavours and those of caramelised sugars, such as toast, chocolate, caramel and occasionally charcoal and ash if very dark. These tend to be far less acidic than light roasts and obviously bitter. Oil is visible on the outside and the beans are very dark brown or black.
Medium roasts are as you might guess, they show characteristics of both light and dark roasts and should always be sweet when well-developed. The body is also heavier or ‘fuller’ here than both light and very dark roasts. It is sometimes difficult to tell apart sour and bitter so viewing this article will shed more light on the difference.
Other names for roast colours
Around the globe, these other terms are used for different roasts. Starbucks now have a blonde roast, which they define as light. This however, by many coffee professionals, would be described as medium-dark. These other terms may also refer to the highest internal temperature of the bean during roast. Here they are:
Light roast – Light city, half city, cinnamon.
Medium roast – City, American, breakfast.
Medium-dark roast – Full city, after-dinner.
Dark to very dark roast – Vienna, Espresso, French, Italian, Continental, burnt (that’s my term!)
For further context, the table on this page of coffeereview is a nice representation.