Before starting the roasting session the roaster has to be cleaned thoroughly. The regulator & burner are used to control the flame. The roaster has to be preheated to 100 degrees centigrade before the Green coffee is loaded into the hopper. The beans absorb the heat from the surface of the drum till they reach 180 degree centigrade. During this process the bean lose moisture content, shrink in size and then the chemical changes begin to happen inside the bean. The time taken to roast each batch of coffee beans is 20-25 minutes. We call this as the roast time. It also depends on external factors like the external temperature, heat transfer and the type of coffee beans which are being roasted. The Coffee bean has a very complex structure of compounds which break down as the as the temperature increases inside the bean.
The bean starts changing its colour from green to Yellow, then brown and subsequently dark brown. The chemical changes which take place inside the bean are called pyrolysis. As the temperature reaches 210 degree centigrade, the pressure inside the bean increases and we hear a crackling sound which is called the First Crack. At this point the colour of the coffee is medium brown. As it nears 225 degrees Centigrade, we can hear the Second Crack and the bean colour turns Dark Brown. At this juncture the Flavour and aroma is optimum. The exhaust Fan is switched on to send out the smoke and cool the hot Beans dropped in the cooling tray. For the flavour and aroma to be retained, the hot beans have to be brought to Room temperature before they are packed and shipped. The coffee beans stay fresh and develop full aroma in 20 hrs from the roast time. They retain the freshness for 7 – 10 days.
We have a fully equipped small batch coffee roaster - a drum roaster which has a capacity to roast 10 kilograms per Batch. The roaster has a temperature control Gauge to record the temperature inside the drum. A sampler is fitted into the drum to check the roast style. The drum rotates over a Burner with Flame supplied by a LPG source. The roaster is fitted with a Hopper through which we load Green coffee into the drum. The drum rotation is controlled by a motor and Belt. Each batch of roast takes around 20 minutes. The Hot beans are transferred into a cooling tray which is fitted with a rotating handle to move the hot beans and an exhaust to remove the smoke and heat from the hot beans.
The coffee is roasted to a temperature of 230 degrees centigrade and should be brought down to the room temperature for retaining the aroma. The next batch is loaded and the process is repeated. At the end of the session the roasting machine has to be cleaned for any formation of carbon or soot inside the drum or the walls of the Exhaust pipes. The quality of the roasted beans is affected if the roaster is not cleaned and properly maintained after every roast session. The roaster machine should have a lot of open space to ensure that there is enough air to remove the external and internal heat.