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Conical VS Flat Burrs: What You Need To Know
Written by: Garrett Oden
The conical vs flat burr debate is opening a pathway for the specialty coffee industry to evolve. Do you want to get in on the debate?
Your typical home burr grinder is going to feature conical burrs. You won’t find any flat burrs in the running unless you’re looking to spend close to a thousand dollars - at least for now. There’s no need to worry though - both burr types produce coffee grounds worth brewing and celebrating.
The times are changing, however, and I’m sure flat burrs will begin appearing in less-expensive devices over the next few years.
If you want to get a leg-up on understanding how the two burr types function differently and why you may want to choose one over the other (if you ever get the chance), read on.
Fair warning though: it’s about to get technical.
Conical Burrs - The Industry Standard
If you pop open your tiny hand grinder, a larger electric grinder, or a higher-end batch retail grinder you would find at a grocery store, you’re going to find conical burrs.
This burr type uses an outer serrated burr and a cone-shaped (that’s what conical means) center burr. As the center burr spins, the sharp edges pull whole beans into the grinding area, where they are broken down into smaller and smaller pieces.
The shape of the burrs allows for fairly uniform grinding with a high level of grind size control. It also is a very efficient shape that allows for lower-rpm grinder, which results in less noise and heat. Overall, conical burrs are not very expensive to manufacture.
Here’s where it get tricky and the debate begins.
Conical burrs produce a bimodal distribution of coffee grounds. This means that if you were to take coffee ground by conical burrs and place it under a microscope, there would be two distinct sets of particle sizes: small and large.
This holds true at all grind size settings - it will always happen with this burr type.
These two sets of particle sizes are what the world is used to and have played a massive role in developing espresso over the last century, in good and bad ways.
The smaller set of grounds (fines or micro-grounds) restricts the flow of water in an espresso basket, which allows the larger grounds more time to extract and produces a heavy, sometimes silky, body. By the time the larger grounds have experienced a balanced extraction, the smaller ones have over extracted and contributed bitterness to the final cup.
Imagine a stereotypical shot of espresso. It’s intense, a little bitter, and has a thick body. That’s what conical burrs do best in espresso. It’s classic, but without a truly uniform (unimodal) distribution, it’s also limited to this realm of flavor and body.
The potential of espresso exploded a few years ago when flat burrs entered the 2013 World Barista Championship spotlight. The world’s most talented coffee professionals experienced espresso like never before, and the debate evolved into what it is today. You’ll understand why in just a moment.
Conical Burr Pros
- High Level of Control
- Low Heat
- Low Noise
- Low Cost
- Low Energy
- Heavy Body, Rich Flavor
Conical Burr Cons
- Bimodal Distribution (Imbalanced Flavor)
- Limited Realm of Possibility
Flat Burrs - A New Espresso Frontier
Flat burrs for espresso grinders are not new, but the realization of their potential is.
Flat burrs are shaped quite differently than conical burrs. Two donut-shaped burrs with razor sharp edges face each other. As whole beans are fed into the whole, they are grabbed by the inner teeth and forced through to the outside of the burrs, where the teeth are more frequent and precise.
Since the burrs are facing each other parallel to the counter, they retain a large amount of grounds between the sharp teeth. Conical burrs don’t face the same problem because the grounds can fall from the bottom of the burrs, instead of being shot out the sides.
Since beans spend more time with flat burrs than conical burrs, there’s more friction involved, which generates more heat. It also takes a stronger motor to spin the flat burrs, which produce a loud high-pitched noise.
You may think that flat burrs are inferior because of the extra heat, energy, and noise. For some, that’s the end of the argument, but it’s hard to say it’s settled once you’ve tasted the difference.
Flat burrs accomplish unimodal distribution. If you were to look at the grounds under a microscope, you would not be able to find two sets of ground sizes. There would only be one.
With this level of precision and uniformity (and lack of micro-grounds), a skilled barista can pull espresso shots all over the board.
He can pull that classic, gritty and thick shot that so many love. Or he can pull a longer, brighter and sweeter shot. Let me show you how.
How Flat Burrs Affect Extraction
Generally, most espresso drinkers prefer a shot of espresso that has extracted 18-22% of the coffee bean mass into the brewed coffee. Less than 18% and you end up with sour, weak coffee (under extraction). Over 22% and you most likely have a bitter, dull, and muddy flavor (over extraction).
If the fines from the bimodal distribution aren’t present and extracting too quickly, you only have to worry about one grind size. Instead of having to balance the bitterness of the fines and sweetness of the larger particles, you can just focus on one size and one rate of extraction.
Matt Perger, the famous World Barista Champion from 2013 who brought flat burrs into the spotlight, advocates for espresso shots extracted at 25% and beyond, which was unheard of before recent years.
With unimodal distribution at this level of extraction, you don’t have bitterness from micro-grounds like you would expect with bimodal grounds. You have a very ripe and sweet flavor (depending on the coffee, of course). You can pull shots twice the size of the classic espresso. You can manipulate flavor like never before, uninhibited by the ever-present micro-grounds.
This opens up a new world of espresso flavor and body and has paved the way for greater creativity from baristas willing to push the envelope. I believe that, before long, that larger realm of possibility will be available to regular home espresso enthusiasts as well.
Flat Burr Pros
- Unimodal Distribution
- Higher Extraction % Enabled
- Greater Espresso Variability and Creativity
Flat Burr Cons
- High Heat
- High Heat
- High Energy
- High Noise
What Does This All Mean For You?
Firstly, if you read through all of that, bravo! You are more educated on this issues than 99.9% of the world’s coffee industry already.
If you’re just looking for a good cup of black coffee, conical and flat burrs are not much of a concern for you. Sure, flat burrs may eventually enter the home brewing arena, but their effectiveness lies more so in espresso brewing.
If you’re looking for an excellent espresso grinder for your home, you may still want to hold off on the flat burrs. Grinders that feature flat burrs are quite expensive, and you’ll still be very satisfied with the quality of conical burrs.
I cannot give you a definitive answer on which burr type you should pursue. If there was a clear and obvious answer, there wouldn’t still be any debate. It’s up to you to determine which type will match your needs and unique circumstances.
However, I can tell you that we're giving away our #1 rated burr grinder for FREE when you sign up for the JavaPresse Coffee Club.
Club members get specialty coffee that was shipped just two hours after it was roasted - so you know it's crazy fresh and delicious. And it's perfect for the new grinder... get yours right here!