Your grinder is one of the most important pieces of coffee equipment you’ll own, whether you’re a café owner or a home brewer. A poor-quality machine will result in an uneven grind size, which in turn will cause inconsistent extraction rates and a muddy cup.
Using a burr grinder will significantly improve your coffee’s quality. Since burrs grind with pressure rather than through chopping the beans, they result in fewer tiny fragments, or fines, than a blade grinder. Yet there are two different types of burrs you can choose from: flat and conical.
What’s the difference between these burrs? How do they affect the precision and consistency of your grind size, as well as the risk of coffee retention? Should you buy a conical or flat burr grinder? Read on to find out.
Lee este artículo en español Molinos de Fresas Cónicas y Planas: ¿Cuál es la Diferencia?
Credit: Dalla Corte
What Are Conical & Flat Burrs?
With a burr grinder, coffee is ground through pressure as it passes between two surfaces or burrs.
Flat burrs are made up of two rings that lie flat on each other. They are often horizontally aligned and have angled teeth. It is the distance between the rings that determines the size.
With conical burrs, however, the grinding happens vertically. One burr sits inside another. The outer burr is a circular, hollow ring with angled teeth. Picture a cupcake wrapper without the base, and you’re pretty much there. The inside burr is conical with a larger base. If you look at it from above, it can appear star- or flower-shaped. This is because it has channels that help the beans to funnel through. It also has small angled teeth.
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How Does Burr Shape Affect Your Coffee Quality?
Grind consistency, retention, and temperature – all of these can affect the quality of your espresso shots and filter coffees. And all of these are to some degree affected by the burr shape.
Marco Beltrame, Coffee Trainer and Technician at Dalla Corte, tells me that it’s difficult to achieve the same level of grind consistency with conical burrs as with flat burrs. This is due to how they’re assembled.
“The biggest difference between conical and flat burrs is during the assembly and construction of the coffee grinder,” he says. “In conical burrs, it is necessary to achieve perfect parallelism and perfect concentricity, while with flat burrs, only parallelism is important. Therefore, it is easier to obtain better homogeneity of the particle size.”
In fact, he believes that flat burrs will always outperform conical burrs. “The more the parallelism is perfect, the higher the granulometry precision will be. In conical burrs, it is impossible to have perfect concentricity, given that the lower burr will have to be mounted on the motor shaft and therefore it will certainly remain decentralized from it.”
In other words, the difficulty in creating an exact alignment with conical burrs can lead to small inconsistencies in the grind size.
However, there is one thing that can cause issues with a flat burr grinder’s consistency: heat retention. Flat burr grinders have a reputation for heating up more throughout the day than conical burr ones. This is because flat burrs require more mechanical power.
Marco stresses that this depends on how the grinder has been manufactured. “A coffee grinder with flat burrs can get very close to the conical temperatures if it’s built with the necessary technical precautions, such as proper ventilation and speed of grinding,” he says.
He uses the Dalla Corte burrs as an example, telling me that “the 65 mm burr diameter and the 1400 RPM of the motor are important for obtaining a not-high peripheral speed and lower heat.”
However, the extra heat could cause issues for cheaper grinders.
Cole Torode of Rosso Coffee Roasters, several-time Canadian Barista Champion and a Dalla Corte Coffee Ambassador, tells me, “If a grinder heats too much, it’s going to change the consistency of the grind size…
“As your day progresses at the café and the ambient temperature in the room is starting to go up, you’ll feel that your grinder temperature is more than likely also starting to go up and I would assume that your shots are going to start extracting faster as the grinds are heating up, because they become slightly more soluble.”
This means that baristas working with flat burr grinders will have to pay careful attention to the temperature. If it rises too much, they’ll need to adjust the grind size for their espresso shots.
Credit: Jean Pierre Flores
Coffee Retention & Contamination
Coffee retention, where grinds are left behind in the machine, can result in varying dry-coffee weight, altering your espresso extraction. Perhaps even more worryingly, it can cause contamination, with stale grounds mixed in with fresh ones.
Retention happens when ground coffee sticks to surfaces within the grinder. This is more likely to happen with flat burrs than conical ones because of how the coffee feeds out of the machine.
With flat burrs, the coffee is pushed sideways out of the burr set. This takes a lot of force, and to achieve this, the grinder’s engine rotates at a higher RPM. Conical setups, in contrast, require less mechanical force as gravity is helping the grains to feed through. This means the risk of retention is lower.
However, Marco stresses that retention can be reduced in flat-burr grinders, based “on how the grinding chamber and its outlet mouth are built”.
Credit: Dalla Corte
Ease & Convenience of Use
Ease of use often has more to do with the grinder design than the burrs, but there are a few differences between conical and flat sets.
The noise is probably the first thing you’ll notice: conical burr grinders run at a lower RPM because gravity is doing a lot of the work for them. As a result, they are usually quieter.
However, like most things, grinder manufacturers can take additional steps to reduce noise. “To reduce the grinding noise [in Dalla Corte machines], one burr has six more grinding teeth than the other,” Marco tells me.
And as we’ve said above, flat burr grinders can also require more adjustments throughout the day as the temperature rises, unless they have a good ventilation system. Again, this is due to the higher RPM.
Credit: Dalla Corte
It’s Not Just About Burr Shape
Burr shape has an impact on the quality of your coffee, but it’s not the only thing you should look for.
Marco says, “Regardless of flat or conical grinders, the workflow is determined by how the entire grinder is made, the diameter and design of the grinders, the motor and its speed, the ventilation, and the whole machine body.”
Pay attention to whether the grinder burrs have been designed specifically for espresso or for a variety of beverages. Marco tells me that Dalla Corte’s burrs are “around 300/450 microns” to make them suitable for espresso, while some grinders are designed to be more flexible instead.
Some people also have a preference for ceramic or metal-alloy burrs. Ceramic is harder than steel, which means the burrs will stay sharp for longer. Yet it’s also more brittle. Small stones and other objects can end up cracking them. Ceramic also absorbs less heat – however, most of the heat generated in grinding is due to the RPM and the crushing of the beans. In reality, there is little difference between ceramic and metal burrs. Most manufacturers opt for metal ones.
Credit: Dalla Corte
Conical vs Flat Burrs: Which Is Best?
The answer is: it depends.
Generally speaking, flat burrs are more consistent and more expensive. Depending on the model, they can also be noisy and, unless there is good ventilation, heat up quickly.
In contrast, most conical burrs are quieter, cooler, and cheaper, but less consistent.
You need to work out which aspects are important to you. Are you operating a specialty coffee shop where precision is key? Or are you an early riser looking for a basic home grinder that won’t wake up the rest of the family?
Remember that burrs are important, but they’re not the only thing that determines grinder quality. Is the machine well-built? Is it appropriate for the drinks you want to make? Is good support available if you need it repaired or replaced?
Once you have the answers to these questions, you’ll be able to make the right purchasing choice.
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Written by Ivan Petrich. Featured photo credit: Jean Pierre Flores
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