Light roast, medium roast, dark roast…what does it mean and which to choose for your daily shot?
Roasting is the process that brings out the aroma and flavour in the green coffee bean. How it is roasted then contributes to the overall flavour of the coffee. While green coffee beans consist of the same acids, proteins and caffeine as the roasted bean, they lack the taste. When heated, the bean expands and changes in colour, taste, smell and density. Oils appear on the surface of the bean during the latter stages of the roasting process.
The absorption of heat in the bean changes its colour from green to yellow to brown, to increasingly darker shades of brown. Light, medium, medium-dark and dark roast are so called because of the colour of brown they become, and is a factor of how hot the beans are allowed to get.
Interestingly, sound is a good indicator of bean temperature during roasting as it makes a “cracking” sound at different temperatures. The first cracking will be heard at around 205 degrees Celsius at which point the bean will have doubled in size with a light brown colour. This is the beginning of light roasts. At 220 degrees C elsius, the colour changes to medium brown, then second cracking occurs at approximately 225-230 degrees Celsius when the beans turn a medium-dark brown creating a full roast. At this point the beans take on an oily shine. For a double roast the beans stay as long in the roaster as they can without catching fire to carbonize the bean’s sugars.
Which roasting profile a coffee roaster uses will depend on the flavour characteristics they are after. The beans will exhibit more of its origin flavour from lighter roasting giving a lighter body and no obvious roast flavour. At the other end of the spectrum, double roasted beans tend to be light bodied but intense with a smokey-sweet flavour.
Here is a guide as to what the different roasts offer when it comes to taste:
Light Roast: For delicate, mild beans to preserve their origin flavour. Usually higher acidity.
Medium Roast: Standard roast profile with full and rich flavour and body. Generally sweeter than light roast with more balanced acidity and aroma.
Medium Dark: Ideal for espresso based drinks, suits milk based coffees
Dark or Double Roast: Strong, smokey and bitter, good for espresso.