Why Shouldn’t I Use the Thermometer that Came with My Grill?

thermometer

A good thermometer is very important for getting consistent and reliable results when roasting with the RK Drum. Most thermometers that come with a grill are horribly inaccurate. Even the thermometers that come with high end, expensive grills do not reliably report the temperature.

The problem with these thermometers is not that the temperature reading is incorrect. The problem is that the thermometer does not give the same reading for the same temperature. That is, if the actual temperature inside the grill is 500°F during 2 different roasts, the thermometer may read 425°F during the first roast and read 550°F the next time.
thermometer

A good thermometer is very important for getting consistent and reliable results when roasting with the RK Drum. Most thermometers that come with a grill are horribly inaccurate. Even the thermometers that come with high end, expensive grills do not reliably report the temperature.

The problem with these thermometers is not that the temperature reading is incorrect. The problem is that the thermometer does not give the same reading for the same temperature. That is, if the actual temperature inside the grill is 500°F during 2 different roasts, the thermometer may read 425°F during the first roast and read 550°F the next time.

To understand why inconsistent temperature readings cause inconsistent roasts, let’s look at what’s happening in the roast. The burners in the grill heat up the grill chamber and the items inside the grill chamber – in this case, the RK Drum and the coffee beans. If the burners are set on low and are letting out a little flame, the grill chamber heats up slowly. If the burners are set on high and are letting out a big flame, the grill chamber heats up quickly. The speed that the grill chamber heats up affects how fast the coffee beans heat up. 

The key to producing excellent coffee is finishing the roast in a specific amount of time.

The recommended time depends on the coffee weight and drum size. (You can find the recommended finish time for your roast in the roast profiles). So, if we want the coffee to finish in the same amount of time (per volume), then we need to heat up the grill chamber to the same temperature each time. But, if the thermometer does not give the same reading for a given temperature every time, it makes setting the heat correctly every time impossible.

flames inside a grill
flames inside a grill

To understand why inconsistent temperature readings cause inconsistent roasts, let’s look at what’s happening in the roast. The burners in the grill heat up the grill chamber and the items inside the grill chamber – in this case, the RK Drum and the coffee beans. If the burners are set on low and are letting out a little flame, the grill chamber heats up slowly. If the burners are set on high and are letting out a big flame, the grill chamber heats up quickly. The speed that the grill chamber heats up affects how fast the coffee beans heat up. 

The key to producing excellent coffee is finishing the roast in a specific amount of time.

The recommended time depends on the coffee weight and drum size. (You can find the recommended finish time for your roast in the roast profiles). So, if we want the coffee to finish in the same amount each time, then we need to heat up the grill chamber to the same temperature each time. But, if the thermometer does not give the same reading for a given temperature every time, it makes setting the heat right everytime impossible.

Wondering what will happen if you just use the thermometer that came with the grill? The most likely symptoms of this problem will be unpredictable finish times and coffee that you can’t reproduce well. You will set the heat, so that the thermostat reads 500°F, for example, thinking that your roast will finish in 20 minutes. But, this time, the thermometer is reading low, and the temperature is really 575°F inside the grill. So, the coffee will roast much faster than expected, and you’ll have 2nd crack in 15 minutes. So what ends up happening is the roast that you previously liked will be not be reproduceable, and you won’t be able to predict the roast or control the roast.  Furthermore, the favorable bean characteristics may not be highlighted if roasted to quickly or too long.

temperature showing the temperature in a grill

The next roast, for example,  you set the heat lower to 450°F, since 500°F caused the coffee to roast to quickly. Now, the thermometer reads high, and the temperature is 425°F inside the grill. The roast drags on and on. After 20 minutes and no sign of first crack, you decide to crack it up to 500°F, but the thermometer is still reading high, and now the temperature inside the grill is still only 475°F. The roast continues to drag on, and finally hits 2nd crack around 30 minutes. When you taste the coffee, it will be disappointing. The long roast time causes the coffee to lose brightness, and the end result will be a baked, blah, boring coffee.

temperature showing the temperature in a grill

The next time, you set the heat lower to 450°F, since 500°F caused the coffee to roast to quickly. Now, the thermometer reads high, and the temperature is 425°F inside the grill. The roast drags on and on. After 20 minutes and no sign of first crack, you decide to crack it up to 500°F, but the thermometer is still reading high, and now the temperature inside the grill is still only 475°F. The roast continues to drag on, and finally hits 2nd crack arond 30 minutes. When you pour out the coffee this time, it does look much more even. But, when you taste the coffee, it will be disappointing. The long roast time causes the coffee to lose sparkle, and the end result will be blah.

In reality, you may not know why no two roasts ever act the same, and you will just find the whole experience frustrating. Perhaps you will give up roasting completely – we hope this won’t happen to you! A quality thermometer is relatively cheap, we offer one for $35, and there are others available from other sources as well. Once you have a good thermometer in place, the roasting process becomes repeatable and much easier to control. The results will be excellent every time, and you will be able to enjoy roasting and drinking your own coffee.

Author: Shane Lewis

Shane is the founder of the green coffee exporter Old Spanish Main, Ltda. in Bogotá, Colombia, having practiced under the renowned grader & cupper Lelly Espitia. He is a cultivator of a #14 Colombian Cup of Excellence coffee. Shane currently designs & manufactures coffee, cacao & grain roasters with RK Drums.

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