The reason why your roast profile temperatures may be different than other people’s or even the profiles suggested here.
One of the key concepts that we need to understand is that we are all building a custom roaster, as unique in many ways as our own personality. We all use a different grill from one make to another model, to another year version, with different BTU’s and so forth.
Furthermore, the heat flow pattern (how the heat flows through the grill chamber) of every grill is going to be different. You may have a horizontal burner, with a left-to-right diffuser plate, you may have 5 burner tubes with a front to rear alignment. All of these things change how heat flows through the grill.
So as a result, where your thermometer is placed, is going to provide you a different reading, than in other places in your grill.
If you are using the built-in grill thermometer, let me be clear that you are rolling the dice on getting predictable and consistent roasts….now and forever. Most of the built in thermometers are utter garbage, yes, even in your fancy Weber… and lie to you about the true temperature. See this article here for further clarification. Time and time again, I get calls from people who are frustrated beyond belief, can’t get any consistency, and are about ready to give up because they can’t get any roast right. Throw out the 45-cent tiawanese thermometer from the same company that makes the little umbrella that goes in your tropical cocktail drink, and purchase something from a company that specializes in thermometers, or pick one up off of the website here. We need adequate and precise temperature control if we are to get consistency in our roasts. My preference would be that you roast with no thermometer at all using just a clock, as compared to a bad one. See this article with more on this subject.
Getting back on track, and to clarify this point, let’s look at some specific examples. Imagine, if you will, placing your thermometer 2 inches away from your fire. The thermometer will read a very high number right? Let’s now move it to the top of the grill, it would read a relatively lower number as compared to the position close to the fire.
So you see, where you place your thermometer has a bearing on what temperature it will read. Further from the fire or closer, sitting right in the the position where the heat wave from the flames can come up and hit the thermometer head on, or in some shielded location where the probe is more protected by the heat diffuser or some other object blocking the heat wave.
While we provide and recommend roasting profiles on this website that work generally well for most people, they may have to be adjusted up or down to get your roast to finish on time, which I will recommend as the most important technique for drum roasting. Understand that our profiles were created using a standard grill with the thermometer installed at the drum level position and should be close to providing a good “relative” profile for you to start with. Nevertheless, this should be considered only a starting point and you will need to adjust your temperatures relatively up or down to compensate for the relative difference in your grill vs. our grill we used to create the profile with.
Finding what works for your situation that allows your volume of coffee for your drum to finish on time is key.