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Roasting technology has come a long way over the past couple of decades. Now more than ever, there are many different types of roasters available on the market, with machine features becoming even more advanced and intuitive.

Nonetheless, heat generation and recirculation still remain two of the most important factors – and both have a huge impact on how coffee is roasted and how flavours develop.

As coffee professionals seek to exert as much control as possible over different variables, convection roasters have started to become more popular. In comparison to machines which rely on conduction or radiation to transfer and recirculate heat, convection roasters are typically more efficient and consistent.

So how exactly do these machines work and how can roasters get the best results? To find out, I spoke to Daniil Samsonov, Managing Director of Typhoon Roasters, and Aaron Davis, co-owner of Doe and Fawn Coffee Roasters.

You may also like our article on how drum and fluid bed roasters affect coffee flavour.

WHAT ARE CONVECTION COFFEE ROASTERS?

Heat is a key element of the roasting process. There are several ways that machines generate and recirculate heat, and each one influences how we roast coffee:

• Conduction – heat is transferred through direct contact (i.e. when coffee beans touch the surface of the drum)
• Radiation – electromagnetic waves generate and recirculate heat, which can be somewhat difficult to control
• Infra-red – when infra-red rays “penetrate” the beans and roast them
• Convection – heat is transferred through the air, so the coffee isn’t in direct contact with the machine

Regarding the latter, many agree that it takes a more modern and efficient approach to roasting. As hot air flows into the machine, it lifts up green coffee beans and circulates them around the roasting chamber. This means hot air is in constant contact with the surface of the beans during the entire roasting process, which results in greater uniformity and better consistency.

Daniil Samsonov is the Managing Director at Typhoon Roasters – a roaster manufacturer which has been designing machines for over ten years.

“Convective heat generation and recirculation provides a more stable heat source for roasting coffee,” he explains. “Air is evenly distributed throughout the chamber, which gives roasters more control over the process.

“In turn, you achieve more consistent results and can optimise energy efficiency,” he adds. “Convection also allows for more precise temperature control, leading to more consistent flavour profiles batch after batch.”

Drum vs. fluid bed roasters

While traditional drum machines rely on conduction to roast coffee, fluid bed roasters use convection. 

The way it works is relatively simple. When using a fluid bed machine, the heating element and fan fill the chamber with hot air. This lifts up the beans and continuously circulates them to ensure even coverage.

Meanwhile, with drum roasters, the chamber is repeatedly rotated so that the beans aren’t in contact with the surface of the machine for too long. If this does happen, roasters run the risk of burning or “scorching” the coffee.

Aaron Davis is the co-founder of Doe and Fawn Coffee Roasters in Milton Keynes, UK. He says that because of these issues, fluid bed roasters are often a more dependable option.

“I believe many roasters prefer convection because you reduce the likelihood of scorching and tipping,” he says. For context, tipping is when the temperature inside the chamber is too high, so the beans absorb too much heat. This can leave dark burn marks on the edges of the coffee beans, which, of course, negatively impacts flavour.

“Convection roasters also offer more uniform roasting,” Aaron adds. “We want to have precise control over airflow and temperature.”

WHY CONSISTENCY IS SO IMPORTANT FOR ROASTING COFFEE

To maintain a loyal customer base and strengthen brand identity, roasters need to create repeatable roast profiles. By controlling different variables – such as charge and roast temperature, air flow, and time – they can highlight a coffee’s best qualities. 

Understanding the science behind roasting is a big part of this. Essentially, it comes down to three chemical reactions:

• The Maillard reaction – also known as “browning”, when amino acids and sugars react to produce melanoidins (which gives food its distinctive brown colour)
• Strecker degradation – amino acids react with carbonyl-grouped molecules to create compounds such as aldehydes and ketones. These are essential to developing flavours and aromas in coffee
• Caramelisation of sugars – complex carbohydrates are broken down into smaller compounds to bring out the sweetness in coffee

To ensure repeatability, consistency is key. Although different machines have their own pros and cons, convection roasters are less affected by external factors, such as air temperature and humidity levels. This is because the air is heated and recirculated only inside the chamber, which creates more stable temperatures.

While roasters still need to keep an eye on temperature, it means they can focus more on other variables, including timing of first crack and rate of rise (or RoR).

“Without question, consistency is the main reason we choose convection roasters like Typhoon,” Aaron explains. “Being able to repeat roast profiles accurately time and time again is very important.”

The benefits of convective heat transfer

Choosing the right kind of machine is one of the most important decisions that any roaster can make. While it ultimately depends on what works best for their business, convection roasters offer a number of advantages.

One of the most obvious is how the machines heat coffee. During roasting, the layer of air that forms between the beans and the surface of the chamber prevents them from coming into contact with each other. 

Moreover, the air acts as a buffer to ensure both the coffee and the chamber remain at the same temperature – further minimising the risk of developing roast defects. These can include underdevelopment, overdevelopment, and baked coffee (when the beans are heated for too long without reaching first crack).

“Our roasters actually lift the coffee during the roasting process, so contact with the metal is minimal,” Daniil explains. He adds that Typhoon’s fluid bed technology evenly distributes heat through a horizontal grid, and then continuously rotates the coffee beans throughout the roasting process.

Productivity is also another key component of choosing a roaster. With roasters’ margins becoming tighter and tighter in the wake of volatile coffee prices and rising inflation, operational efficiency has never been so crucial.

Daniil tells me that Typhoon Roasters can produce up to six batches per hour at maximum load, with the average roast time ranging between six to eight minutes. He adds that because the machines’ convection technology optimises temperature stability, Between Batch Protocol (or BBP) can be much shorter than when using other machines. This term refers to the process of resetting the thermal energy in the roaster from the last batch to the start of the next batch – and has a huge impact on roast profile consistency.

THE SWITCH TO CONVECTION HEATING

As roasting technology becomes more and more intuitive, many roasters have started to invest in convection machines to leverage these features to their advantage.

Ultimately, the move towards convection machines impacts how businesses roast their coffee – and thereby how consumers experience flavours and aromas. 

Aaron explains some of the biggest differences he noticed when switching to convection roasting a few years ago.

“One of the main challenges was getting accustomed to how quickly these machines can roast coffee,” he says. “We reduced roasting time by up to 40% compared to traditional machines.

“We started our business with a 5kg Typhoon roaster just under two years ago, and recently purchased another 10kg machine with an output of up to 70kg per hour,” he adds. “As and when the time comes, we will invest in a 30kg-capacity roaster to keep up with demand.”

Achieving the best results

As the coffee industry continues to embrace automation, roasters are increasingly reliant on technology to support them in their job roles. Using different platforms and software allows roasters to closely monitor and control numerous variables, while also focusing on other areas of the business.

Daniil tells me that Typhoon machines can be connected to third-party platforms like Artisan and Cropster. This helps roasters to record a wide range of accurate data, including first and second crack times, charge temperatures, batch drop times, and RoR. By analysing this data and changing variables accordingly, roasters can get the best results from their coffees.

“Our machines allow businesses to optimise productivity, maintain coffee quality, and achieve consistent results,” Daniil adds. “Roasters can thereby improve both operational efficiency and customer satisfaction.”

There are many types of roasters available on the market, and each one has an important purpose. While some coffee businesses may prefer using more traditional machines, others have started to switch to more modern roasting technology.

Convection coffee roasters are at the forefront of this shift. Ultimately, if a business decides to invest in these machines, understanding how they work – and therefore how they change the way we roast coffee – is the first step.

Enjoyed this? Then read our article on how roasters can control airflow.

Photo credits: Typhoon Roasters, Doe and Fawn Coffee Roasters

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