Roasting Coffee


I got the opportunity to setup and tune a commercial coffee roaster recently. I’ve been roasting coffee in various small coffee roasters for years. A couple of them I built, a couple I bought. I’ve never had the chance to roast on a real drum roaster with variable controls until this showed up one day…


This is a 2KG machine and will roast about 5lbs at a time. It’s quite a different experience to roast on a capable machine. Roasting coffee is cooking, and cooking is mostly about applying heat. With the thermal mass of the machine plus the beans, input adjustments (heat, air) translate to delayed changes in temperature within the mass of beans. This means you need to make adjustments minutes ahead of when you need them. Making the correct adjustments to the inputs over the duration of a roast is know as roast profiling. And yes, of course there is open source software to help you with that. I chose Artisan as it’s open-source and has a large user base. Artisan basically monitors the three thermocouples installed in key spots in the roaster, you can manually apply markers to the developing profile to study how your input changes affected the roast. Here is a recent graph of some Sumatra Mandheling I roasted on this machine:

You can develop really precise profiles using this method

The prominent light blue line seen decreasing from left->right is what’s known as the Rate-of-Rise (ROR).  The ROR is one of the must fundamental and important indicators of how your overall roast is progressing. In short, you want an ever decreasing ROR. You can see in this plot, I didn’t accomplish that. Hitting a correct ROR is not easy on a new machine.

I enjoyed the process so much that I decided I needed my own. Subsequently this showed up:


This roaster is slightly larger than the previous one. It will roast about 8lbs at a time, or around 40lbs an hour. More to come on the destination for this machine in the future…