Refer a friend and get 10% off our online shop.
Roasted coffee is literally one of the most chemically complex beverages we can put in our mouths and the generation of theses incredible flavourful aromatic compounds is largely down to the chemical changes that occur within the seed of the coffee cherry when it is inside a coffee roaster.
If you’ve ever tried to brew up a cup of the good stuff using raw green beans, the importance of the roasting process becomes apparent very quickly. Firstly, they are structurally much harder and subsequently less soluble than their roasted counterparts making it more difficult to grind and extract flavour from the beans. They also offer very little in the way of that typical coffee flavour that we all know and love, instead tasting vegetal and pea-like.
We roast coffee to ultimately enhance it, allowing this agricultural product to reach it’s full potential with respect to aroma and flavour. Specialty coffee is some of the most tasty and exciting coffee in the world and we strive to showcase the beautiful, inherent characteristics each bean holds thanks to the emphasis on quality within the supply chain. When roasting we are looking to develop positive taste attributes such as aroma, sweetness, acidity and body. Whilst at the same time attempting to avoid negative flavour traits such as bitterness, baked and roasty notes.
Green coffee contains around 250 aromatic molecular compounds, and it’s these compounds that are responsible for a coffees flavour and aroma. Through roasting that figure increases to 800+, giving us a whole host of desirable characteristics. The tasty flavour notes you see on the outside of your coffee bags be it fruity notes, hints of nuts or chocolate, even floral aromas akin to what you’d find in standout African coffees.
Roasting makes this increase happen. Once heat is applied to these seeds a whole host of chemical changes within each bean begins to occur. Hundreds of chemical substances undergo change. Some of them diminish, some disappear, some transform and some combine with each other to form new substances.
On a physical level we see a change in colour, an increase in size, decrease in density and increase in solubility. Both chemical and physical changes that ultimately help to determine that delicious coffees flavour.
The goal of roasting is to take something that’s unpalatable and not only make it palatable but to make this flavour accessible. The roasting process opens up the bean and makes it possible to appreciate the development of beautiful flavours. It make the beans brittle enough to grind easily and porous enough to allow water to access and extract their soluble flavour. In short, roasting not only makes drinking this mighty fine beverage possible, it also creates one hell of a tasty experience for the tongue.
THE ROAST PROCESS
Now the roast process begins with what we call the CHARGE, which refers to the temperature at which the green coffee beans are dropped into a coffee roaster. This is determined depending on batch size and is important as it helps establish the momentum needed for the duration of the roast. Once the temperature within the drum meets the desired charge temperature for that batch, the green beans are dropped into the roaster which signals the beginning of the roast process.
Next up is the turning point, which helps create the s-curve that we see in a typical roast profile. In most roasters temperature data is gathered from a probe within the drum. This measures the temperature of air when empty and beans surface when roasting. When green beans enter the drum from the hopper they are at room temperature and this results in a noticeable drop in temperature within the roast chamber, not surprising seeing as the drum can be in excess of 200 degrees before the charge. Once the temperature of the air and beans equalises it reaches the ‘turning point’ and the curve begins to rise creating the signature ‘tick’ of the roast profile.
Generally, it is common practice to refer to the rest of the roast process in ‘phases’ as a way of explaining and simplifying the changes occurring within the bean throughout the duration of a roast.
If you roast passed first crack, the temperature of the bean continues to rise and CO2 begins to build within the bean again. This pressure forces oils to the surface and a ‘second crack’ occurs, releasing excess CO2 for a second time. We choose not to roast into second crack here at North Star because we feel this destroys much of a coffee’s unique character. Desirable flavour compounds begin to degrade and are eventually lost. Simultaneously, reactions generating unpleasant bitter compounds begin to increase yielding pungent roasty notes that overwhelm whatever subtle flavours survive dark roasting.