If you've ever read many boutique roasters websites you probably see them talk a lot about their roasting machines. Why? Because how we apply heat to the coffee while roasting changes the chemical reactions that happen, and ultimately the flavor.
Avoiding going into a long soliloquy about grilling meat or other cooking analogies, let's dive into some difference between the two roasting apparatus that we've posted about so far, and demonstrate how you may alter your practices at home, or choose what is right for you.
We've been roasting in a cast-iron pan, and a carbon steel wok. If you haven't read our introductory how-to's, and you are new to roasting you can do that in these links:
Now let's examine each of the pans a little further
Cast Iron
Pros
- Gentle even heat source
- Thermal Stability
- Better for darker roasts, or building more body and depth in coffee
Cons
- Low sides make it easy to spill coffee beans while stirring
- excessively hot pan can cause scorching
- difficult to alter roast on the fly
Cast Iron is one of the most popular materials for drum roasters among artisan coffee roasters. In fact reading some marketing materials you may even believe that this metal is embued with magical powers which impart unique and exquisite flavors to coffee beans while roasting. The truth, is that the advantages of this metal are quite practical, and generally revolve around the mass (or weight) of the drum itself. Cast Iron is heavy, and that heft changes the way that we are using heat when roasting the coffee.
More specifically the mass of the pan acts as a damper to changes in in temperature. If we start with a cool pan, it will take longer for the cast iron to heat up, and thus slow down the heating of our coffee beans inside. This however can work in the opposite direction, once our pan is hot it is going to be difficult to cool it down.
This is why in our how to, we recommend to start with a cool pan, or only slightly warmed pan, so that we can gently heat the beans at the beginning. It is also why we recommend lowering the heat at or just after first crack. Once the pan heats up, we don't need to keep applying as much heat as the pan is already hot, and has excess heat to give off to the beans.
Wok
Pros
- High sides are great for stirring
- Thermal Reactivity - easy to alter roast on the fly
- Better for lighter roasts, or more acidity and brightness
Cons
- More burner tweaking required
- excessively hot pan can cause scorching
- more challenging to repeat roast results
Carbon steel is not really used in commercial or industrial roaster production, and I believe that it is because the heft of cast iron makes it less likely to warp over time, and a better choice in that application. However in our case, we don't have a rotating cylinder making 1000's of revolutions, and which the shape makes an important difference to the function.
What we can gain from carbon steel is that we have a rather thin sheet of metal that will be more reactive to changes in our burner input of heat. This means how we use the flame can be very important. This may make it difficult to repeat our results exactly, but it can also make the process more fun.
Which are you going to choose? What have been your experiences? We'd love to hear from you.