Hot Air Drum Roaster vs. Traditional Drum Roaster: A Roastery Owner's Guide

Choosing the right coffee roaster is one of the most significant decisions a business can make. The type of roaster you use has a direct impact on the flavor profiles you can achieve and the consistency of your final product. At Artisti Coffee Roasters, we often get asked about the difference between our IMF hot air drum roaster and a traditional drum roaster.

Let's dive into the core principles of roasting and how these two technologies compare.

The Two Principles of Heat Transfer

In coffee roasting, there are two primary methods of heat transfer:

1. Conductive Heat: This occurs when the coffee beans make direct contact with a hot surface, such as the metal drum. Think of a sausage on a barbecue plate—the heat is transferred directly from the hot surface to the object.

2. Convective Heat: This is the transfer of heat through the movement of a fluid (in this case, hot air). The beans are surrounded by a heated environment, and the heat is transferred through the air.

Both traditional and hot air drum roasters use a combination of these methods, but they differ significantly in how they control the balance between the two.

How a Traditional Drum Roaster Works

A traditional roaster relies heavily on conductive heat.

• Heat Source: A large gas burner located beneath the drum heats the metal.

• Conductive Transfer: The coffee beans tumble and make direct contact with the hot drum, cooking them from the outside in.

• Convective Transfer: A fan at the back of the roaster pulls hot air through perforations in the drum and over the beans. You can modulate this airflow to control the convective heat and remove smoke and chaff.

While effective, the challenge with a traditional setup is that it's difficult to separate and control the two heat sources. The heat from the burner directly influences the drum's temperature, and the convective airflow is secondary, primarily used for venting.

The IMF Hot Air Drum Roaster: A Different Approach

The IMF roaster flips this balance, giving priority to convective heat with a precise, on-demand hot air source.

• Integrated Afterburner: The IMF uses a single, powerful afterburner that operates at around 600°C (1112°F). This afterburner not only eliminates smoke and odors but also serves as the primary heat source for roasting.

• The Vortex System: Instead of heating the drum from below, the IMF injects a controlled stream of this superheated air directly into the roasting drum. This air is mixed with ambient cold air to achieve the exact temperature we've programmed. This "vortex" system allows for a huge amount of heat on demand, which can be precisely controlled at any point in the roast.

• Heat Reticulation: A key innovation of the IMF system is its efficiency. The hot air that has passed through the beans and out of the drum is then pulled back through a separate tube, routed through the chaff collector, and recirculated back into the afterburner. This full reticulation system means very little heat is wasted, making the process incredibly gas-efficient and environmentally friendly.

Key Differences and Advantages

It's important to clarify that the IMF is not a "hot air roaster" in the sense of an air roaster that fluidizes beans in a chamber (like a popcorn popper). It's a drum roaster that uses a hot air source, which gives us the best of both worlds: the flavor development from a traditional drum roast with the precision and control of modern hot air technology.

We've been amazed by the control and consistency this technology provides. It allows us to draw out specific flavors from our beans with an accuracy that would be difficult to achieve on a conventional machine.

For a visual look at how the IMF's unique heat system works, check out the digital animation from IMF themselves: https://youtu.be/OScEVAMB0o8

If you have any questions about roasting or these technologies, leave us a comment below!