September 19, 2022

Understanding roast curves on modern coffee roasters


As technological change becomes more and more frequent in the coffee industry, we are seeing more roasters invest in modern equipment, including machines which can use advanced roasting software.

Although these modern machines certainly have their benefits, transitioning away from traditional models requires extensive planning, especially when it comes to translating or redeveloping roast curves.

In fact, some industry professionals feel that traditional roast curves are becoming outdated as the specialty coffee sector continues to grow – meaning investment in training is essential for many roasters.

To understand how roast curves are changing, I spoke with three coffee professionals. Read on to learn more about their insight.

You may also like our article on using roast curves to guide the roasting process.

Female barista operating coffee roasting machine in coffee shop

Exploring traditional roast curves

Effectively, a roast curve is a graph which indicates how temperature changes during the roasting process. The first point on a roast curve is the “charge temperature”, which is the temperature of the drum before the beans are added. Once the coffee is added, the temperature sharply decreases.

From this point onwards, the temperature gradually increases – which is why it’s known as the “turning point”. The point at which this occurs, as well as the pattern of temperature increase, can be plotted on an axis of time against temperature – creating a graph which generally forms a curve.

In order for a roaster to achieve their desired roast profile, the temperature inside the drum must be carefully controlled. The measurement of the rate of temperature increase is referred to as the “rate of rise” (RoR). 

The higher the RoR, the steeper and quicker the roast curve will be. Throughout the roast process, beans lose more moisture and roast temperatures can decrease – meaning the curve becomes flatter and steadier towards the end of the roast.

The RoR is one of the most important variables in roasting, as it allows roasters to achieve their desired profile more effectively and efficiently.

David Rozali is the owner of Rozali Coffee in Berlin, Germany. He explains that as roasting technology has evolved, data has become more and more important to roasters – including first crack timing, development time ratio, end temperature, and both outer and inner bean colour.

Using this data, roasters can develop more precise profiles to produce consistent and uniform batches – leading many to invest in more modern equipment.

Most roasters believe the “S-curve” to be a more traditional and straightforward roast curve which usually results in a medium profile. It can be a great starting point for less experienced roasters and can even allow for further experimentation with different profiles.

Man using a coffee roasting machine in Sweden

What is a “modern” roaster?

Lisa Gringl is a former Product Manager at Cropster. She explains that while “modern roasters” can be a broad term, Cropster has its own general definition.

“Cropster defines roasting technologies launched over the past ten years as modern roasters,” she says. “This could include machines with heat transfer or automation systems, as well as equipment which uses smart technology to support the roaster.”

She adds that software integration has become a significant component of roaster design in recent years. Many newer machines include highly sensitive probes which can provide roasters with a greater range of more accurate information than older equipment.

Some manufacturers are also incorporating artificial intelligence-powered technology into their machines to predict variables such as first crack.

“It’s important to understand what data the machine can provide and how it can be shared with customers,” Lisa says. “As a result, roasters can improve the quality and consistency of their coffee.”

Alongside this, sustainability has also become a widely-discussed topic within coffee roasting, and with that, energy use. 

While more traditional roasters rely on gas to heat up, some modern machines are more energy-efficient. Some examples include either using electricity or recycling heat and exhaust fumes to reduce “startup” costs as far as energy is concerned. 

How are roast curves different on modern machines?

Given the advancements in roasting technology, roasters are now able to make more precise adjustments to profiles in a more efficient manner.

David agrees, saying that data from modern roasters is much easier to interpret, but there are differences in the roast curves used on these machines compared to more traditional equipment.

“[With a modern roaster], the roast curve and RoR will look different because of the thickness and placement of the probe, as well as how hot air circulates within the drum,” he explains. “With a Loring, for instance, the turning point tends to be sharper and occurs earlier.”

Jason Richter is the owner and Head Roaster of Path Coffee Roasters in Port Chester, New York.

“Newer roasters can roast coffee faster, which produces a very different curve,” he says. “It has a high peak and then it slopes down. 

“With a Probat roaster, you would get a much more angular curve,” he adds. “On a Loring, it’s a much higher peak, and then it drops and starts to trail.”

Understanding the differences in roast curves on traditional and modern equipment can be challenging for some roasters. Roasting software can help to bridge the gap between older and newer machines for less experienced roasting professionals.

However, despite the ability to have more control over roast profiles, David highlights that roasters still need to have a thorough understanding of how their machine works.

“A roaster is a tool,” he says. “Every roasting professional needs to understand their machine so that they can use it to get the best out of their coffee.

“If the roaster is inexperienced, they could potentially ruin the batch,” he adds.

A person preparing freshly roasted coffee beans at River Trail Roasters, Redmond, Washington.

How has software made the transition easier?

Lisa believes that automated roasting technology and software have developed to become more equipped to keep up with the ever-growing demands of roasters and their customers.

“Cropster’s First Crack and Bean Curve Prediction features can create a smooth transition from one roaster to another,” she says. “The AI features have been programmed using data from thousands of different machines.

“The company works closely with roasters to access data from their machines,” she adds.

However, adapting to a new roaster can be challenging, as David explains.

“Previously, I have used a Probat P12 and a Probat UG22, before purchasing a Loring S15 Falcon,” he says. “There isn’t much difference between the roasters, but there were a few variables I needed to pay attention to when using a Probat.”

He tells me that he had to be more observant with a more traditional roaster, especially to avoid any roasting defects, such as scorching. With a more modern machine, he says that software is often able to automatically prevent errors, as well as storing any data he might need to tweak his preferred profile.

Jason agrees that new roasting software has helped to maintain more consistent roast profiles.

“As we’re based in northeast New York, the winters are cold and dry and the summers are warm and humid,” he explains. “With traditional roasters, it was a balancing act to maintain the profile throughout the year.”

Although making data more accessible helps to increase coffee quality, some industry professionals are concerned that roasters could be overwhelmed with too much information. 

User-friendly software can certainly help with this, but for less experienced roasters, it could make it difficult to understand roast curves for more modern machines.

Woman putting coffee beans in the coffee roasting machine

What are some of the benefits of modern roasters?

Generally speaking, modern roasters aim to simplify the roasting process, automate as much as possible, and democratise roasting data. 

For instance, roasters may be able to upload profiles which have been developed for a specific coffee, and then automate the batch. This allows the machine to control most of the variables rather than requiring the roaster to stand over it for the duration, tweaking heat and airflow.

David says this allows roasters to focus on other areas of their business, such as scaling green coffee sourcing.

“Automation is a great feature to have on your roaster,” he tells me. “It provides higher levels of consistency and it makes it easier to train staff when expanding the company.”

Before this became more accessible, roasters would have to manage every variable themselves, meaning there was the potential for human error. For instance, during busier periods on older machines, roasters could forget to implement temperature or airflow adjustments at the appropriate time, which could in turn negatively affect coffee quality.

“With some modern roasters, you just need to adjust your initial gas setting depending on the day,” Jason says. “Beyond that, the software will heat the roaster based on the set temperature and can roast entirely on its own.”

It is also still possible to manually control the roasting process on modern machines, meaning roasters can continue to make adjustments if necessary.

Understanding roast curves is a key part of the roasting process. Ultimately, this means industry professionals need to understand them as much as possible – whether using a traditional or more modern machine.

But with more and more roasters switching to more modern machines, making a smooth transition possible is becoming increasingly important. After all, it’s key that roasters can easily incorporate, adjust, and redevelop their roast profiles to improve and maintain coffee quality.

Enjoyed this? Then read our article on streamlining quality control in your coffee roastery.

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