Beyond coffee packaging: How drum speed impacts quality

Esther Gibbs
January 3, 2024
coffee packaging, custom coffee bags, drum speed, RPM, Nirvana Soul Coffee,

One variable rarely mentioned within coffee roasting is the drum speed of the roaster. It is often omitted as smaller roasters lack control over drum speed. Therefore, when first introduced to roasting, people are unable to delve into how it impacts the roast. 

The drum speed of the roaster, also commonly referred to as drum revolutions per minute (RPM), can significantly impact the flavour and development of coffee. Beyond this, an incorrect drum speed may lead to roast defects–something no amount of custom coffee packaging can hide. 

I spoke to Alex McClean Egan, the head roaster at Nirvana Soul Coffee in California, to uncover some foundational elements about drum speed. 

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Breaking down drum RPM

A traditional drum roaster will use a rotating drum with an energy source, heating both the drum surface and the air inside. Therefore, the drum speed can be sped up or slowed down to change the transfer of energy.

Alex has been in the specialty coffee industry for over 10 years, working their way up from barista to management, and now Head Roaster. Alex explains they enjoy balancing both the science and art of coffee to create the perfect cup.

“Drum speed refers to how many revolutions per minute the drum rotates within the roasting chamber,” they explain. “Or put more simply, it’s how quickly the drum moves in the roasting chamber.”

Essentially, drum speed determines how much movement the coffee has during the roast. Therefore, a slower drum speed will move the beans around a lot less than a faster rhythm. “Drum speed can increase or decrease the amount of conduction heat that coffee beans experience during a roast,” Alex adds. 

Conductive heat transfer (or conduction) is a traditional form of roasting akin to frying: the beans come into direct contact with the hot drum and cook from the outside in. In Ethiopian culture, roasting by conductive heat is common practice. Using a large pan (called a metat dish), the roaster will cook the raw coffee beans over hot coals, moving them around regularly to achieve an even roast. This is one of the most simple ways of roasting coffee.

Conduction plays a particularly important role at the beginning of a roast when room-temperature beans are dropped into the hot drum.

coffee packaging, custom coffee bags, drum speed, RPM, Nirvana Soul Coffee, Alex McClean Egan

How to perfect drum speed

Determining the correct drum speed can be a challenge. “If the drum speed is too low, you will likely see the coffee collecting towards the bottom of the drum,” Alex explains. “This means some beans are touching the drum for a long time while others are not touching the drum at all. This will result in an uneven roast.”

In this case, you’re likely to find a combination of beans: some that are darker in colour and overdeveloped, others that are lighter. Sometimes this may even scorch some of the beans, resulting in an oily or smoky taste in the cup. Beyond this, extraction will often be inconsistent in brewing. 

“Alternatively, if the drum speed is too high, it could lead to the coffee being pushed up to the side of the drum due to centrifugal force,” Alex notes. “This leaves almost no room for the necessary balance of convective and conductive heat, again leading to an uneven roast.”

Coffee roasters need to understand their machines and the impact of RPM, as each roaster is likely to have different settings. For instance, the material the drum is made from and how it is heated will affect how you set the drum RPM. 

“I always encourage trial and error where possible,” Alex says. “If you have old coffee, see if you can throw it in and manipulate the drum speed to be an RPM you don’t usually use,” Alex adds that coffee roasters should take note of how the coffee in the drum sounds, as well as how the beans look and smell. “And then of course cup it. If possible, I would try to do a side by side cupping with your usual roast versus the experimental roast.”

Alex adds that there are many different schools of thought when it comes to maximising the potential of your drum speed. It is important to acknowledge and investigate research other people have executed. That said, the best way to learn is to experiment for yourself. 

“Some say drum speed can be used for different-sized batches, ”Alex says. “Some say it depends solely on the size of the drum itself. But I say, do what you want, but do it safely! If your coffee tastes good and your customers like it, then that’s a win in my book. So if that means messing around with drum speed, I fully support it.”

coffee packaging, custom coffee bags, drum speed, RPM, Nirvana Soul Coffee,

How to ensure consistency to promote brand loyalty

Within coffee roasting, there are no ‘one size fits all’ rules. Every coffee and roasting machine differs, but everyone’s end goal is the same: ensuring the coffee is something your customers enjoy.

Alex’s experience with manipulating drum speed has been varied. “When I’ve manipulated drum speed in the past, I’ve focused on the bean itself. If you have a high density coffee that you want to roast around the same length of time as your average coffee, I suggest you bump up the RPM a tad.”

Alternatively, if you’re roasting a robusta, Alex suggests experimenting with a lower RPM. “Remember, what you are changing when you change drum speed is how the heat is being transferred into the bean. So, balancing the conductive and convective heat transfer, no matter the drum speed, is the most important thing with this variable.”

Understanding heat transfer is a crucial part of roasting. In addition to educating yourself from other people’s experiences, execute multiple roasts with varying degrees of drum speed to improve your understanding. Be sure to change it throughout the roast and analyse the coffees with tests on density, and moisture content, as well as flavour and taste. 

This can also help to build up your sensory memory which you can use to analyse future roasts and make knowledgeable adjustments to your drum speed in the future. 

In addition to offering specialty roasters and coffee shop owners’ custom-printed coffee packaging made from 100% recyclable and sustainable materials, MTPak Coffee updates the Education Centre daily. The free resource provides those in the coffee industry with a wealth of information around sourcing high quality green coffee, roasting tips, as well as the latest in roasting and packaging trends.

Images courtesy of Nirvana Soul Coffee

For more information on custom-printed coffee packaging, contact our team.

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