Learn about the key stages of coffee roasting and discover why you're coffee can taste so different from roaster to roaster. The speed at which the coffee beans pass through each stage is called the roast profile. Roasters try to keep the coffee consistent by ensuring the roast profile for each bean is kept exactly the same each time. There are really only two variables important to coffee roasting - temperature and time. By careful variation of these two important factors it is possible to bring out different qualities of the coffee bean that each roaster wishes to accentuate.
So what are the basic stages that the coffee bean goes through during the coffee roasting process? Here they are...
Stage 1 - Drying
The raw coffee bean starts off containing around 10 - 12 percent moisture. The coffee roaster is usually preheated when the raw bean is first loaded in and during the initial few minutes it looks like nothing is happening. During this stage the bean is warming up and the water contained inside is beginning to evaporate. A large amount of energy is required for this first part.
Stage 2 - Browning
So the beans have dried out and they now begin to brown. In some cases the coffee beans go quite a bright yellow before turning brown. The aroma at this stage resembles cooked rice. The browning reactions going on inside the coffee bean cause it to expand and it begins to shed it's thin papery skin (the chaff). This chaff is a fire hazard so hot air is constantly passed over the beans inside the roaster to blow it away into a special chaff collector, which is attached to the exhaust of the roasting machine. At this stage the smoke starts (although most of it may still be steam).
Stage 3 - First Crack
Once the so-called first crack stage has been reached, gases and water vapour have been building up inside the coffee bean and it begins to emit an audible cracking sound when the pressure is finally released. The sound is very similar to that of pop-corn, although a little quieter. At this stage the coffee bean has been roasted enough to be used to make coffee. Although it's up to the roaster to decide at what point the roasting stops. They may continue a little longer.
Light roasted coffee is usually stopped on or just after the first crack stage and you'll usually get the real flavour of the bean at this point. Although it is generally true that the acidity will be quite high and you may get a lot of sourness - especially when making an espresso.
Stage 4 - Roast Development
Here is where the delicate art of coffee roasting comes into it's own and much of it boils down to the opinion of the roaster. The flavour of the end result is mainly governed by how long the coffee bean is subjected to heat after the first crack stage. The longer the time, the less the acidity and sweetness as the sugars and acids are caramelised. Think about the sweetness of sugar syrup compared to caramel and even molasses (treacle). As the heat is applied to sugar, the less sweetness is present. The same is true inside the coffee bean.
The coffee bean becomes browner and the surface smoother. There are various terms to describe the roast level during this phase: from "cinnamon" to "city" to "full city" - it's essentially the medium roasted phase and the coffee undergoes a transformation into something wonderful!
Stage 5 - Second Crack
At the end of the development stage the beans begin to crack again. This time it's a quieter more crackly sound and signifies that the structure of the bean is beginning to break down. They become darker, oils will appear on the surface and they start to look a lot more shiny. Beyond second crack is the French or Italian roast stage and, essentially, the original and unique flavour of the coffee has been lost. The bitterness is high because the coffee has essentially been burnt.
If you want to explore the different flavours of each origin then these dark roasts are not for you. The uniqueness has gone and a coffee from Brazil will taste very similar to one from Ethiopia.
Stage 6 - Coffee Drinking
Sorry, did I say 5 stages? Of course, this is the bonus stage!
If you'd like to try out some of our lovely freshly roasted coffee beans, visit our coffee bean shop.