The natural heat that the wood fire gives off is important because, like with a gas roaster, the wood flame has no direct path to the bean.
Roasting coffee with gas heaters results in a moist heat, whereas with electric heaters it results in a very dry heat. Wood produces a natural, dry heat and enhances the aromas in the beans. The result is less acid in the coffee , a softer and milder taste and more crema (coffee foam).
The main difference between wood and conventional gas and electric roasters is the quality of the wood heat and the roasting time . While conventional roasters need about 15 to 18 minutes (industrial roasters at 900 degrees only need 2 minutes), drum roasters with wood fire take up to 25 minutes .
The moisture in the beech wood creates what is known as gentle heat, stopping the drying phase of roasting. This extends the entire roasting process, preserving the natural lipids inside and leaving significantly more natural oil in the beans themselves.