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Understanding RoR in Coffee Roasting

By
Jason Jin
September 26, 2022
6
min read
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Users who use roasting software in first time often ask what RoR means. It is hard to explain in one sentence clearly, so I’m going to explain in this post.

1. Predict how the temperature will change

Most coffee roasting machines have two or more temperature sensors. One of temperature sensor is attached to the front panel of the machine and is located inside the drum where coffee beans hit. This temperature sensor is a thermometer to measure the temperature of coffee beans during roasting. In Firescope, it's marked with green lines.

The formula for calculating the RoR value is temperature increase / time increase * unit time.

In the Bean Temperature graph below, the value of RoR can also be expressed as the slope of the green line. Expanding the line with this slope allows you to predict how the temperature will change in the future. The Bean Temperature expected dotted line drawn on graph are drawn by calculating RoR in Firescope.

The expected temperature dotted line helps you predict how quickly or slowly coffee bean will reach a particular temperature at the desired time. For example, if you know the temperature at which the primary crack is reached, you know when. RoR determines that roasting is fast or slow and also helps control the firepower.

This is the first reason to observe RoR. If you use Firescope as your roasting software, you'll know intuitively.

2.Predict more accurate temperature progression

Then you might wonder why the software draw BT RoR chart continuously. This is because there are things that can be interpreted even with the trend of BT RoR.

The slope of the BT line is not constant when roasting is in progress. If there is no change in the firepower, the slope is generally lower and lower. Referring to the blue line in the graph below, the slope ends with the maximum slope value after the turning point and then gradually decreasing. Therefore, for the graph below, the gradual decrease in the number of blue lines also slows the rise of Bean Temperature.

3.Guess the situation around the thermometer measurement

I prefer roasting, which is progressing gradually decreasing without significantly changing the firepower. Sometimes the RoR decreases or rises more than the firepower I reduced regularly. In this case, if the thermal power variable is controlled, it may be suspected that an unknown behavior inside the roaster affected the thermometer measurement. For example, the physical change of coffee beans, the change of external exhaust, etc. If you look at the numerical changes in RoR, you can guess what happened just by looking at the roasting chart.

As an example, you can often observe a sharp drop in BT RoR after the first crack. You can see that during the first crack, there is a physical change that slows the temperature rise of coffee beans. A typical reason is that the water remaining in the beans is ejected and the temperature drops rapidly. 

We learned the meaning of RoR in roasting based on BT RoR. If you have any questions or errors in the article, Please contact through email jason@firescope.io and we will answer them as sincerely as possible.


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Jason Jin
Firescope Co-founder
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