Understanding Coffee Roasting’s Environmental Rate of Change (RoC)
As coffee lovers become more savvy with the roasting and brewing process, understanding factors such as Rate of Rise (RoR), bean temperature and environmental temperature all come into question. Environmental Rate of Change (RoC) can help predict the temperature of the roasting drum, and in turn, help maintain control during roasting. Let us explore what environmental rate of change is, why it’s so important to track, and how to control it:
Understanding Environmental Temperature
We can’t understand environmental rate of change without first understanding environmental temperature. This is the temperature of the air inside the drum of the roaster which is measured using a thermocouple, which measure the convective heat in the roaster.
Monitoring the environmental temperature really helps contribute to a good roast. The convective heat present in the roaster through gas and liquids is what is measured to gauge environmental temperature. So, changes to the environmental temperature can affect the desired qualities of a roast, or worse, disrupt a roast entirely.
Predicting environmental temperature behavior can help keep the temperature in control and prevent any sudden changes.
What Is Environmental Rate of Change (RoC)?
RoC measures how the environmental temperature changes with time, and at what speed. It can help predict the behavior of the temperature in the roasting drum and in turn, help control the roast.
It can be likened to the Rate of Rise (RoR) of bean temperature, which tracks how bean temperature changes. This is usually measured using another thermocouple which is placed closer to the bean mass. (See graph below.)
So, how do you read the Environmental Rate of Change (RoC)? A positive environmental rate of change indicates that energy (or heat) is increasing in the drum, while a negative will show you that you are losing energy, irrespective of what the environmental temperature is.
This information is crucial for predicting how the environmental temperature is changing, and in particular, how quickly it’s changing. Tracking this during a roast means you become aware of potential changes in temperature while you’re roasting. It’s also key to creating your roast profile. Along with RoR and the bean temperature, a profile will help you recreate roasts consistently.
All of this data in roasting is extremely important because it represents the different events that are occurring during the roast. All of the tracking you see is critical in order to keep the roasts consistent and maintain the standard of our coffee we create for our customers.
How to Control Environmental Rate of Change (RoC)
Now that we understand what the environmental RoC is, how can we put reading the data into practice? There are a few ways to control it.
The first thing is for us to aware that each roaster (each roast for that matter) is unique. Different materials in the machine will give off and absorb energy at varying rates. Similarly, different probe sizes will interpret temperatures at different speeds. Knowing your roaster and how it reacts with heat and air is critical to controlling the environmental rate of change.
If the RoC of the environmental temperature starts to reduce and flatten, this means that heat is being lost from the drum and the environmental temperature will most likely drop. However, this does not necessarily mean the bean temperature will automatically drop. There are a number of factors that can cause temperature drops such as room temperature, airspeed, drum rotation, gas quality roaster capacity and, of course, coffee quantity. All of these must be taken into consideration, and each variable can help provide the answer to controlling your environmental rate of change.
A positive RoC means that there is enough energy in the machine to keep the bean temperature on a positive RoR. However, if you’re following a roast profile and the rate of change exceeds the data on the profile, it’s possible that one of the variables has not been appropriately managed during the roast.
The environmental rate of change data tells us how quickly the environment temperature is changing in a roaster. Without it, there is a higher risk of unpredictability. Temperature data represents the desired profile of a roast. However, importantly, environmental rate of change represents how temperature within the drum is changing.
When roasting, we don’t want unexpected surprises, so we record the Environmental Rate of Change (RoC) and other data to achieve the highest level of consistency and quality.
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