There’s a number of various grinding-related thoughts rolling around my head at the moment. They’re not fully formed (and possibly red-herrings, so look out!) but I thought I should put them out there. I don’t have any data to back them up, and I’m even sure they’re all true.

As such, this will be a slightly more conversational and open-ended post compared to most of my writings of last year, and I hope many of you can engage with it in the comments below or in the Slack.

1. Fines are Fine

Fines are the tiniest of coffee grinds. I’ve been hearing more and more professionals calling any coffee grind smaller than ~100 microns (0.1mm) in diameter a fine and I’m inclined to agree. They’re the ones that get stuck in your pores, and lend your shoes that unmistakable eau de barista after a shift.

Fines have have a lot of surface area, and not a lot of volume. This means that all of their coffee flavour is pretty much instantly accessible to water. Compare this to a large coffee grind (a boulder) where the vast majority of the flavour is hidden away inside the grind and you’ll quickly see why grind size is such a big deal. For more information on this, head to my early post ‘Surface Area and Time’.

For as long as fines have had a name, it seems like people thought they were evil. “Fines instantly over-extract making your brew taste terrible” being the most common phrase I’ve heard over the years. I’m now fairly certain that’s untrue, and I can’t help but think the complete opposite is more likely.

In 2013 I went to Mahlkonig and ran some tests on the EK43 to figure out why it makes coffee taste so delightful. Turns out it produces many more fines than any of the other grinders in the test at comparable settings. So, best-in-category grinder produces more of the ‘evil’ stuff than any of the others. This was a red flag that kick started my hunt for more answers.

When sifting my coffee for the 2012 World Brewers Cup, I was eliminating all grinds below 250 microns. I had to then lengthen the brew time and increase my extraction to levels higher than I’d ever seen before (+25%). This ultra-high extraction tasted super great, and is very similar to the level of extraction that every fine undergoes during every brew; maximum. Nearly-maximum extraction tasted so good I managed to take home the title. So why do fines get blamed for bad over-extracted flavours when over-extracted but sifted coffees taste great?

Posit: Perhaps temperature/time/roasting is to blame for over-extraction, not fines.

Nearly every brew ever made has had fines in it. And if you think about it, the outer surface of the larger grinds should behave exactly the same as the fines themselves (It’s the inside of the larger grinds that creates the problems). This means that a whole lot of the dissolved coffee flavour has come from “fine-like” extractions. Perhaps, once the roast is of good quality, it’s brew time and temperature that are coaxing out undesirable flavours of over-extraction.

2. Alignment is Key

Grinding burrs need to be parallel, and concentrically and radially aligned to work properly. The tolerances required are miniscule. A misalignment of ~0.05mm noticeably changes the quality of coffee produced by a grinder.

A number of baristas have been experimenting with alignment of their burrs and seeing extraordinary results (hop in the Slack and go to #grinding to see what I’m talking about). Ever since I played around with a Versalab grinder and saw how bad the coffee tasted when the burrs were misaligned, I’ve been very conscious about alignment. Frank at Titus Grinding (@titusgrinding on instagram) has been doing lots of cool things with the Versalab grinder; improving their alignment and surface finishes.

EK43’s have a little bit of play between the burrs and carrier/body. This can lead to misalignment if assembled without care. EK43’s that are aligned well make coffee that’s blindingly obviously better. (I’m currently working on a visual guide for proper alignment, and thinking of building a kit to align the burrs during assembly. Please let me know if you’re keen to buy a jig that does that.)

Alignment is one of those things that’s (kind of) free, and can make a massive difference to coffee quality. I often say VST baskets are the best bang-for-buck improvement you can make to your coffee. I’m feeling like proper burr alignment could be next on the list.

3. Boulders Might Just Be Structural

Lots of Baristas are frustrated with the non-linear relationship between grind size and extraction in espresso. eg. Medium grind = low extraction, Fine grind = high extraction, Finest grind = low extraction. It is assumed that this effect is caused by the grinds becoming so fine that they form pockets impervious to water flow, causing micro-channeling and a lower extraction.

Maybe the larger grinds are also there to provide a structural matrix that prevents the smaller grinds from gumming everything up? I’d be keen to see/do an experiment where fines are mixed amongst larger insoluble particles to see if this carries any weight.

4. Bean Temperature Matters

I’ve been involved in a soon-to-be-published paper on grinding alongside many others. Christopher Hendon and Maxwell Colonna-Dashwood (the authors of Water for Coffee) were the primary masterminds for it, and I’m confident we’ll shed some light on this situation.

Once published, I’ll be posting a version of the paper in regular human English. The ramifications for grinding tech are super interesting.

Is there anything grinding-related that’s got you thinking? Do any of these points seem ridiculous? Hit me up below or in the Slack.