May 11, 2020

What Is The Environmental Rate of Change in Coffee Roasting?


Environmental rate of change isn’t as well understood as Rate of Rise, bean temperature, and environmental temperature. However, it’s just as important, if not more so. It can help predict the temperature of the roasting drum, and, in turn, help maintain control during roasting.

Join us as we explore what environmental rate of change is, why it’s so important to track, and how to control it.

Lee este artículo en español ¿Qué es el Índice de Cambio Ambiental en el Tueste de Café?

What Is 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.

Emerson Nascimento, owner at Coffee Five in Brazil, tells me, “It’s really important to monitor the environmental temperature because convective energy is what makes a good roast. It’s what highlights the qualities of specialty coffee.” This convective heat which is present in the roaster through gas and liquids is that which is measured to gauge environmental temperature.

Changes to the environmental temperature can affect the desired qualities of a roast, or worse, disrupt a roast entirely. Predicting the behaviour of the environmental temperature can help keep the temperature in control and prevent any sudden changes.

You may also like: Coffee Roasting Guide: What Is Airflow & How Can You Control It?

What Is Environmental Rate of Change?

The environmental rate of change measures how the environmental temperature changes with time, and at what speed. It can help predict the behaviour 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, however.

So, how do you read the environmental rate of change on a graph? A positive environmental rate of change indicates that energy (or heat) is increasing in the drum. A negative environmental rate of change will show you that you are losing energy, irrespective of what the environmental temperature is.

This information is vital to predicting how the environmental temperature is changing, and importantly, how fast it’s changing. Tracking this during a roast means you have an awareness of potential changes in temperature while you’re roasting. It’s also integral to creating your roast profile. Along with RoR and the bean temperature, a profile will help you recreate roasts consistently. 

Francisco Supervielle, co-founder of Seis Montes in Uruguay, tells me the similarity in tracking environmental rate of change and RoR is “an important key in order to have consistency.”

Francisco highlights the importance of these two select pieces of data, telling me, “when you are replicating a roast and when you have more data, you are actually able to replicate it even better than with less data.”

All data in roasting is important, representing different events that are occurring. The environment temperature data is key to understanding and tracking a roast. However, the environmental rate of change is arguably more helpful in controlling it.

This control is integral to consistency in roasting and maintaining the standard of your coffee.

How to Control Environmental Rate of Change

Now we understand what the environmental rate of change is, how can we put reading the data into practice? There are a few ways to control environmental temperature and environmental rate of change. 

First, be aware that each roaster 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 rate of change of the environmental temperature starts to reduce and flatten, this means that heat is being lost from the drum, and the environmental temperature will forecast to drop. This does not necessarily mean the bean temperature will drop yet. Francisco tells me there are a number of factors that can cause temperature drops, “drum rotation, airspeed; room temperature; gas quality; roaster capacity and coffee quantity.”

Each variable can help provide the answer to controlling your environmental rate of change.

A positive rate of change 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, you don’t want surprises. Simply diligently record your environmental rate of change and other data to achieve a high level of consistency.

Enjoyed this? Check out RoR, Bean Temperature, & More: How to Use Common Roast Data

Feature photo: Roastery setup with data collection software. Feature photo credit: Francisco Supervielle. Other photo credit: Jean Pierre Flores

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