How does a coffee roaster work?

The process of coffee roasting includes several steps that cannot be ignored. Even though modern coffee roasting machines are packed with advanced technologies, the fundamental rules are always the same. 

Before Operation

Preheat the roaster before before placing green beans into the drum if you are doing the first batch roasting. It is important to preheat the machine because it will help to eliminate the moisture that still is in the raw product. Normally we suggest preheat temperature set above 180℃. For different operators, they may have preferred preheat temperature. 

Start Roasting

Once the drum reached the desired temperature, you can pour the green beans into the drum. You will need to observe their color which changes from light yellow to brown within 5-8 minutes. Along with the brown color, you will smell a fresh scent that is similar to popcorn that just popped. 

First Crack

After around 7 minutes, the size of the coffee beans is being increased. It is happening because the heat and the air pressure form carbon dioxide and monoxide inside the coffee beans that become more voluminous. The temperature inside the coffee roaster reaches 200 or more degrees Celsius, which also increases the air pressure. It presses the walls of the coffee beans, and once it is high enough, the coffee beans start cracking. It has its own name – “first crack”. This is the breakthrough in your coffee roasting process. Not only the shade of brown color changed, but you certainly heard that characteristic sound – once again, it is similar to the popping corn seeds.  


when you achieved the satisfying results, now it's time for cooling. A cooling tray is an important accessory which allows your coffee beans to cool down quickly, without losing the wonderful, fresh aromas. It is also worth to use a destoner, a device that separates coffee beans from stones or other potential objects that came with green coffee beans. Stones and metal pieces can appear even in high quality specialty coffees. Your coffee should rest for a couple of days to de-gas and to develop full-bodied flavors.  


Since you know how does a coffee roaster work, now you can begin your own coffee-roasting adventure. Consider all the differences of coffee roasts, and prepare freshly roasted batches of coffee.