Conical vs flat burr coffee grinders

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No matter how good your beans are, the wrong coffee grinder can lead to you never being able to achieve a consistent and accurate flavour profile.

We all know the importance of having a good quality burr coffee grinder. But we also know that there is more to the decision than just choosing a good brand.

So, before you make your purchase, one of the key things you need to know is whether a conical burr or a flat burr grinder is best.

In this post, we look at the features, advantages, and disadvantages of both in order to help you decide which is right for you.

First things first: What are burrs?

In burr coffee grinders, coffee beans are forced through a gap between two burrs that crush and cut the beans into particles that are the desired size for brewing.

A burr mill, or burr grinder, is a mill used to grind hard, small food products between two revolving abrasive surfaces separated by a distance usually set by the user. – Wikipedia

Flat and conical burrs are the two most common types of burrs available in coffee grinders.

Both sets consist of two pieces that have a gap that is wide enough to allow ground particles to pass through (based on your grind setting).

The conical burr has a ring shape and a cone shape that fit together. Flat burr grinders have two shapes that lay parallel to each other. We’ll discuss their differences in more detail shortly.

Why use a burr grinder?

The two main types of coffee grinders are burr grinders and blade grinders.

Blade grinders use sharp spinning blades to grind the coffee. They are simpler and generally cheaper than burr grinders. The longer the blades spin, the finer the coffee gets.

The main downside of blade grinders is they produce grinds that are not consistent in size. This makes it difficult to create a repeatable process for coffee brewing, as the grind consistency can vary from brew to brew. It also means that extraction may not be even, and parts may be over or under extracted.

Burr grinders, while generally being more expensive, are considered to be much more precise.

They use two ridged metal plates known as burrs to grind coffee. By adjusting the size on the grinder the distance between the burrs will change. When the burrs are close together, a finer grind size is produced; when the burrs are apart, a coarser grind size is created.

The main advantage of burr grinders is that they provide a lot more precision and consistency. They allow the user to make incremental adjustments, which is critical for processes such as “dialling in” an espresso shot.

Conical burr grinders

Conical Burr on the Breville Smart Grinder Pro

Conical burrs have a cone-shaped ring that fits into another cone-shaped ring that is hollow. Beans are directed down along a vertical path, carefully guided by the conical burrs.

The rotating burr works by pulling whole coffee beans into the grinding area where they are crushed and cut into smaller and smaller pieces.

The cylindrical shape of the burrs keeps them from getting stuck together while they’re spinning.

The main advantages of the conical burr grinder relate to its lower RPM design. This means it produces less noise and heat than its flat counterparts.

It also means it requires less energy, which is why it’s the go-to design for hand coffee grinders.

Pros:

  • Affordable
  • High control
  • Low heat
  • Less retention
  • Quiet
  • More efficient

Cons:

  • Bimodal distribution (although this is required for traditional espresso)

Flat burr grinders

Flat burr coffee grinders have two sets of burrs: one facing upward, the other downward. The coffee beans fall between the burrs, are ground through them and are led out the sides by the burrs.

While they are generally more expensive, noisier, and have more issues with heat, they are more precise than conical burrs as they have a unimodal distribution of ground sizes, meaning they are more consistently sized.

However, while they are more precise, the uniform grind size is much more difficult to use for traditional espresso recipes, although is becoming more common in the professional coffee world.

Pros:

  • Unimodal distribution

Cons:

  • Expensive
  • Noisy
  • More retention
  • High heat
  • Less efficient

Bimodal vs Unimodal

Aside from price and availability, the main difference between the two types of burr grinder is that the conical burr produces a bimodal distribution while the flat burr produces a unimodal distribution.

For a regular espresso recipe, you need a two-tiered grind, which is what is delivered by the conical burr grinder. The smaller coffee grounds restrict the water flowing through the espresso puck, providing enough time for the larger particles to be saturated. This two-tiered sizing is known as bimodal.

Flat burrs produce an extremely even particle size, known as unimodal. This means that all the grounds will be almost exactly the same size.

While consistent grind size is generally considered a good thing, espresso has developed with the conical burr shape and therefore the machines themselves and traditional recipes are designed for the bimodal grind size distribution.

Metal vs Ceramic Burrs

Ceramic burr grinders are generally more affordable than their metal counterparts.

They absorb less heat than metal, which is important, as a hot grin chamber can start the extraction process. They also tend to stay sharper for longer than steel burrs.

However, as ceramic is more brittle than steel, the burrs can crack if a small stone makes its way into the grinder, or if you drop it on a hard surface.

Metal coffee grinder burrs are more generally considered to be more precise than ceramic burrs. This is because the burrs can be manufactured to be sharper than with ceramic.

They are also more durable than brittle ceramic burrs.

And while they do suffer from potential issues relating to heat retention, they can also be made from different materials and finished in such a way that they have better cooling capabilities and can still retain precision.

Coffee retention

Coffee retention is the name given to when coffee sticks to the surfaces inside grinders.

Because conical burr grinders rely on gravity to feed the beans through the chamber, they require less mechanical force than other types of grinders. This means that there is less risk that grounds will become stuck.

Retention is more likely to happen if the burrs are flat, as the grounds coffee feeds out of the machine on the burrs, compared to conical burrs, where the coffee grounds fall down themselves.

Conical vs flat burr: Which is best?

For most home brewers, regardless of whether you brew french press or espresso, conical burr coffee grinders will be the best option.

They are easier to use, produce less noise output, less heat, and are cheaper than their alternatives.

Flat burr coffee grinders, on the other hand, offer more precise control and consistency. They are best suited for cafes or other professional coffee environments where they want to take more control of their espresso brewing.