March 29, 2023

How can heat retention & recirculation help specialty coffee roasters to improve efficiency?


In recent months, it’s never been more important for coffee roasters to become more energy-efficient. With rising energy and logistics costs, roasters need to be more mindful than ever of their consumption. This includes the efficiency of the equipment they use.

When it comes to machines, this is especially true – particularly those which include heat retention and recirculation technology. Not only can these systems help to reduce energy consumption, and thereby decrease costs, they can also help to cut emissions.

Moreover, given that demand for sustainable coffee is only growing, it’s vital that roasters pay closer attention to their environmental impact.

To learn more about how heat retention and recirculation in coffee roasting work, as well as the benefits of these systems, I spoke to Alessandro Garbin, the CEO of IMF Roasters. Read on for more of his insight.

You may also like our article on how you can reduce emissions during coffee roasting.

IMF vortex towers used for coffee roasting heat circulation.

What are heat recirculation and retention in coffee roasting?

Before we discuss how heat recirculation and retention work, we first need to look at the types of heat transfer in coffee roasting.

There are two types of heat transfer when roasting coffee:

  • Conductive heat transfer: this is when heat transfers between two objects that are in direct contact. For example, when a coffee bean touches the surface of the roaster drum or another bean.
  • Convective heat transfer: this happens when heat transfers through liquid or gas. This type of heat transfer can be natural or intentional.
    • Natural: hot air will rise to the top of the roaster drum
    • Intentional: using a fan or pump to force cool air into the roaster drum

Radiation heat transfer is also used in coffee roasting. This is when heat is released as a result of the vibrational and rotational movements of molecules and atoms. This means it’s almost impossible for roasters to control this type of heat transfer.

Conductive heat transfer also isn’t as prominent in coffee roasting as convective heat transfer. As such, it’s key for roasters to efficiently control it.

As well as utilising some kind of heat source (usually either gas or electric), most roasters have an in-built fan or pump. When in operation, both of these systems work to continuously intake air and heat it to roast coffee. A roaster’s ventilation system will then remove the smoke and waste gases from the machine.

Heat recirculation systems

Alessandro explains what heat recirculation is in the context of coffee roasting.

“Machines reuse air which has already been used to roast coffee,” he says. “After the air is cleaned using high temperatures, it can be used again inside the drum or roasting chamber.”

A roaster’s heat source and ventilation system are constantly working in unison. This means that air is continuously heated and reheated throughout the roasting process.

However, for roasters which come with recirculation systems, they can reuse hot air. To achieve this, the recirculator removes waste products – such as exhaust gases, chaff, and smoke – before returning the hot air to the drum or roasting chamber.

Some roasters also come equipped with more than one heat recirculation system, which can provide a number of benefits.

IMF’s Vortex system works by mixing ambient air with hot recirculated air before it enters the drum or roasting chamber. 

“The temperature of the air which needs to be recycled and reused from the drum or roasting chamber can often become too high,” Alessandro says. “The Vortex system then mixes this hot air with fresh, cooler air so that it reaches the optimal temperature for the required roast profile.”

Meanwhile, the Equaliser system maintains the same volume of hot air both inside the drum and surrounding its surface. This helps to distribute heat more evenly.

“IMF’s Equaliser system ensures a more uniform heat transfer to every coffee bean so that roasters can achieve a more even and homogenous roast profile,” Alessandro explains.

A coffee roaster operates IMF roasting equipment.

Why is heat circulation so important for roasters?

To maximise profitability, there are many factors that roasters need to consider. Among these are cost management and retaining customers by ensuring your roasted coffee is consistently high in quality.

Heat circulation systems can allow roasters to effectively manage both of these factors.

Many older machines tend to include an afterburner, which purifies air by heating it up to very high temperatures. However, while afterburners do help to reduce emissions, they also require gas to run.

For many roasters, increasing gas usage to reduce emissions is not always cost-effective. However, heat recirculation systems don’t rely on gas – meaning roasters can lower both their environmental impact and energy costs.

“Heat recirculation technology can help to make sure that emissions from roasting fall within the limits imposed by current regulations, [although this depends on where you are located],” Alessandro says. “You also don’t need to integrate any additional abatement systems, such as thermal systems or catalytic converters.”

It’s an understatement to say that demand for more sustainable coffee is increasing – especially among younger generations. This statement rings true across the entire supply chain, including with roasting.

IMF roasters include a double-function heating chamber which recycles used hot air and heats it to very high temperatures,” Alessandro explains. “This way, when some of the air is emitted into the atmosphere, it’s already clean, while the rest can be reused during the roasting process.

“Moreover, this means the volume of air emitted from IMF’s roasters is lower – [maximising heat recirculation and reducing gas consumption up to 47%],” he adds.

An IMF roaster on display inside a roastery.

How does heat retention affect day-to-day operations?

First and foremost, as conduction and convection are the two main types of heat transfer, recirculation systems help to make sure that heat distributes more evenly in the drum or roasting chamber. 

If heat is distributed unevenly, this can lead to a number of issues for roasters. One of the biggest concerns would be uneven roast profiles. This is when some beans are underdeveloped and others are burned or scorched. Not only does this create an inconsistent product, it will also significantly impact the flavour and quality of coffee.

“Not all heat recirculation systems guarantee a constant air temperature during roasting,” Alessandro says. “High-quality roasters like IMF ensure a consistent temperature by incorporating fresh air into the drum or chamber, which allows for greater thermal stability.”

Improving consistency

Furthermore, as machines become progressively hotter throughout the day, some roasters find it difficult to maintain consistency between batches. With better heat retention systems, temperature variance between roasts will decrease, which inevitably improves roast profile consistency.

Alongside maintaining coffee quality, heat recirculation systems can help to reduce costs in the long term. When lower volumes of air are reheated, roasters are able to reduce their energy usage, thereby reducing energy costs and lowering their carbon footprint at the same time.

Finally, Alessandro offers advice on how to make sure heat recirculation and retention systems keep running efficiently in your roaster.

“As with any roaster, it is recommended to regularly clean and maintain your machine so that it lasts for a longer time,” he concludes.

A closeup of IMF roasting equipment that uses coffee roasting energy efficiently.

For any roaster looking to become more energy-efficient, it’s clear that investing in a high-quality roaster is key. However, managing costs and keeping emissions down will become easier if roasters keep an eye on heat retention and recirculation technology.

In doing so, roasters will be able to manage their energy consumption much more effectively. In turn, they are likely to experience a decrease in their costs, as well as their environmental impact – both of which are more important than ever before.

Enjoyed this? Then read our article on how coffee roasters can design an appealing and efficient roasting space.

Photo credits: IMF Roasters, Better Days Coffee Company

Perfect Daily Grind

Please note: IMF Roasters is a sponsor of Perfect Daily Grind.

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