As I mentioned before, the grinder with the smallest median and mode is the EK43 with coffee burrs. As you would expect, the extraction yield in this case is also the highest.
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The EK43 is also producing the largest fine peak (the bump down around 80um). But if you think about it, that peak is barely more than the other grinders even though the grinds are so much smaller. Essentially, the EK43 can break coffee beans apart many more times without experiencing a drastically increased number of fines. This is one of the reasons why you can extract more with an EK43 without experiencing dryness or unacceptable bitterness.
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The mean and mode are the smallest, and this also works in the EK43’s favour when you think about even extraction. Measuring extraction yield is an average; every grind of coffee extracts slightly differently and then you mix them all together. Half the grinds might be way over-extracted and the other half might be totally under-extracted, but the extraction yield will tell you the number that’s right in the middle. This isn’t a flaw of the science, it’s just the way coffee is. When you have a grinder that’s producing a wide spread of particle sizes, you’re going to get a wide spread of extraction yields that are averaged to give you a single number. The tighter your spread of particles, the higher your extraction can get before tasting bad.
If you have a lot of larger particles, you’re really going to struggle to extract a lot out of them. This creates a big problem; where the smallest particles are being completely over-extracted, and the smaller particles are being completely under-extracted. The resulting brew will be simultaneously sour/vegetal and bitter/dry.
This is a little chart that helps explain what I mean about different sized particles creating different flavours in the brew. As you can see, the larger particles are extracting less, and the finer particles are extracting more. All of them are contributing something to the brew, then once it’s all mixed together we take a TDS reading.
The ‘Theoretical Extraction Yield’ row is what I think the average of that ‘band’ of particle sizes is extracted to. Then, the two rows below that denote the percentage/volume of each vertical band (0-90um, 90-200um, 400-800um, 800-2000um). You could also call these rows ‘% Sample Composition’.
If you did a bit of maths on these numbers, you’d find that it all adds up to 23.3% extraction for the EK43 and 20% extraction for the Robur (the real-world results of this test) so my Theoretical Extraction Yield numbers aren’t too far off what’s actually happening!
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If your spread of particles is really small, you can reach much higher extractions. The largest (but still relatively small) particles are raising your average, which means that the smallest particles don’t need to be so over-extracted to lift that average. This creates a much more focused and intense flavour where a lot of the grinds are sitting at, or close to, the desired level of extraction.
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The entire spread of the EK43 is really fine. Compared to the other grinders, it almost looks out of place. This is the other (rather counterintuitive) reason as to why you can extract so much more with the EK43; because the fines are very similar in size to the rest of the grinds. Instead of ‘fighting’ the fines, and pushing them really high to extract enough out of your median grinds, you’re actually using them to contribute tasty extraction to the average. To help explain, I’ll exaggerate a little bit and also introduce a concept called ‘extraction spectrum’; that being the range of extraction %’s that are contributing to your averaged extraction yield.
Pretend you have some coffee sieves that allow you to isolate grind sizes exceptionally well. You have three pairs of sieves that give you grinds right on 50um, 250um and 600um (the mode of the fine peak, EK43 and Robur, respectively). If you were to brew these individual samples the same way, I imagine the 50um would extract to 26%, the 250um would extract to 21% and the 600um would extract to 16%. The extraction spectrum of each of these samples is extremely small. All you could taste in those brews is that exact level of extraction – no average, no mixing – just intensely focused flavour resulting from one % of extraction.
Now lets recreate our grinders from the test, by mixing these samples together. To imitate the EK43, I’ll mix 1 part of the 50um with 9 parts 250um. To imitate the Robur, I’ll mix 1 part of the 50um with 9 parts of the 600um.
[This is a really simplistic and inaccurate example but it proves a point so please bear with me.]
The resulting extraction of the EK43 sample might now be 22%.
The resulting extraction of the Robur sample might now be 18%.
The EK43’s extraction spectrum now has a spread of 5% (21-26%), while the Robur’s extraction spectrum reaches across 11% (16-26%). The flavour of the EK43 brew will be very focused, while the Robur will taste muddled.
This means that if you want to increase the extraction of the Robur brew, you might be able to get more out of the 600um grinds, but as you do that the 50um grinds’ extraction % will also increase, becoming aggressively dry and bitter. The EK43 is naturally extracting 4% more, so you’re tasting more sweetness and transparency, without the 50um grinds being totally blown out.
With the EK43, the fines are much less of a problem than they are with the other grinders because they become a positive component of the brew.
We use the EK43 at St Ali for a large proportion of our coffees. The baristas on bar now refuse to use any other grinder, and aren’t enjoying coffee at other cafes as much any more. It has completely changed the way we roast (for the better) and has eliminated an incredible amount of stress formerly originating from misdiagnosed roast/green coffee faults. I cannot recommend this grinder enough!
Part Four and Five of this series (unpublished) will detail how we use the EK43 on our bars, and how to get the most out of it.
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