Heat transfer through a clay furnace in a coffee roasting machine to produce coffee with a distinctive aroma

Roasting is the stage where coffee beans develop specific organoleptic properties in terms of taste, aroma, and color. The roasting process is a process that depends on temperature and time where the coffee beans undergo a series of reactions that cause some changes in their chemical composition. These two parameters will determine how high the quality of the coffee beans produced even though they come from the same type of coffee beans. From a technological point of view, roasting is a process that originates from the forced flow of electrically produced hot gases to roast green coffee beans into mature coffee. In Indonesia, local clay materials have long been used to create various containers for combustion at high temperatures, including coffee roasting. The weakness of clay walls as a heat conductor is the length of roasting time but this material is to produce a distinctive aroma and taste. To overcome this, innovation is needed in the coffee roasting process. Therefore, the purpose of this study was to determine the heat transfer process in a roasting machine with a modified clay-walled combustion chamber using a forced flow system (semi hot air flow). Based on the experimental results, it was found that the heat formed through the hot air flow was higher in temperature than the heat from the combustion chamber walls. This happens because there is a layer of clay 10 mm thick and clay is a lower heat conductor than aluminum. But in terms of aroma, taste and color of the product, the combustion chamber with a layer of clay can produce better coffee characteristics than aluminum.