Understand the impact of different heating methods on roasting in 5 minutes

Original text: A Guide to Different Heat Types in Roasting Equipment

by Zach Latimore

Roasting coffee is a management of heat aimed at altering the physical and chemical composition of coffee beans. As Candice Madison, the roasting director of Royal Coffee, a raw bean supplier, said, "Roasting is actually playing with heat

We know that different types of heat supply are generated during the roasting process, and their effects will vary during the roasting process. Let's review conduction heating and convection heating, and how to improve roasting results by regulating them.

Main types of heat

There are three ways to transfer heat:

1. Thermal conduction in coffee roasting

Thermal conduction is simple: heat transfer between two objects in direct contact. When you touch something that has just come out of the oven and burn your hands, it is conductive.

In coffee roasting, if any type of heating element (such as a flame) comes into contact with the drum, heat conduction occurs when the coffee beans come into contact with the surface, paddles, or panels of the drum, or even when the coffee beans come into contact with each other inside the roaster.

The role of conductive heat transfer in the coffee roasting process is smaller than you might imagine. Candice pointed out that even in drum roasting machines, only about 30% of heat transfer comes from conductive heat transfer.

2. Convective heat in coffee roasting

Convective heat is the transfer of heat through liquids or gases. When you turn on the hot oven and feel a gust of hot air blowing towards your face, it is convective heat.

There are two types of convection: natural convection and forced convection. Natural convection describes the natural trend of hot air rising and cold air falling. Forced convection is the process of forcing air to transfer heat through a fan or pump. Almost every roasting machine uses a fan to some extent to draw air into its roasting machine. However, natural convection also occurs in drum roasting machines, where the air at the top of the barrel is often hotter than the air near the bottom.