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Ever sieved your ground coffee?

February 15, 2012

Before you file this under “crazy talk” and click away, consider thinking about what you expect your grinder to do when you flip it on. If you’re not totally asleep, you’ve typically chosen the correct setting for your brew method in advance and now expect the coffee to come out uniformly ground to your specifications. Except that no grinder is perfect! It seems to be in the nature of coffee grinding that even the best burrs will produce a measurable amount of fines on coarser settings. What you want in the non-espresso range is to minimize this inconsistency, i.e. to narrow the distribution of particle sizes.

But how does a sufficiently motivated person go about measuring grind consistency? Eyeballing it on a white sheet of paper (or similar) is a *start*. Your tongue works better; inconsistency will lead to underextraction of boulders (perceived as sourness) and relative overextraction of fines (perceived as bitterness). But, frankly, these instruments can be imprecise. A sieve is better in many ways—though not perfect, as I’ll point out toward the end. Plus, to ice the cake, sieving your coffee will reduce sediment if your preferred brew method normally allows some into the cup.

I’ve started playing around with sieves out of pure curiosity lately and figured it was time for a post summarizing what I’ve observed. Eventually I may adopt the method to semi-formally compare grinders since I have a LIDO coming soon. That is, unless Orphan Espresso’s ongoing sieve study makes mine irrelevant! Last I heard, they were planning to compare the Baratza Preciso, Baratza Vario, OE PHAROS, and OE LIDO, using a Ditting as a baseline.

For my first experiment, I turned to a common Chefmate kitchen strainer with what seemed to be fairly fine mesh that I had on hand to sieve my Preciso’s press grind (setting #34F, if it matters). I didn't know how big the spaces were in the metal mesh, but a 1000-micron (1.0-mm) steel ball bearing didn't quite fit through them. Anyway, I gave 21.9 g. of my press-ground coffee a thorough shaking using this strainer and ended up with 20 g. of ground coffee remaining. Only 8.7% loss. Not bad, right?

What was sieved out:

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A closer look:

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Bottom of the cup brewed afterward in my Eva Solo 0.6 L (damn, I missed a few fines!):

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About that brewed cup, I thought it had a slightly cleaner flavor profile. I’m not sure it was cleaner in a *good* way though.

The second time around, I decided to devote a portion of my PayPal coffee slush fund to the purchase of a proper sieve. However, a little research revealed that these things were expensive! As in $30 or so each new and up. Even used, testing sieves (usually made of brass or stainless steel) were going for more $$ than I’d expected, so I knew a whole set wasn’t in the budget. I set my sights on one particular sieve size (among many), #20, because it’s the one that’s become a de facto standard for coffee cupping; according to the SCAA, a fairly coarse drip grind should be used for that purpose—specifically, one with 70-75% of the particles passing through a #20 sieve. Not that I plan on becoming a pro cupper or anything. I just thought it was cool, and the mesh size (850 microns or 0.85 mm) seemed to be in the ballpark for clarifying the press-style cups I usually brew with grounds in the 1200-micron range (an estimate).

Here’s what I ended up with via eBay for $20 shipped: a 20-year-old, 3-in. brass #20 sieve in mint condition that does a predictably nice job of filtering out particles below 0.85 mm.

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Allow me to geek out for a moment by highlighting an aspect of this sieve’s high build quality. That grayish stuff around the outer edge where the mesh meets the rim is solder, and it’s been applied by hand in such a way that no square holes are partially blocked. The result is a bit of a jagged-looking outer edge, true, but perfectly uniform openings across the mesh surface. I can’t see how it would have mattered if some of those outer square holes were smaller than the others due to solder smearing, but the attention to detail makes me happier than I would have expected. Using this thing makes me think of my grandfather. It’s a quality tool.

When I ground 20.1 g. of coffee using the same setting as before on the Preciso (#34F) and sieved it, this time I was left with 16.8 g., i.e. 16.4% loss. So, the strainer I'd been using before must have finer mesh. Sadly, I didn't get to brew the results due to a diaper-related emergency that needed handling (NB: the baby's diaper, not mine). 

One last thing for now: if I were to get serious about sieving for analysis purposes, I’d need a controlled way of agitating the sieve. Why? Because the more you shake, the more coffee passes through. A grinder doesn’t carve coffee beans into cubes, after all, and a given particle that’s stopped by a 0.85-mm square hole when oriented one way may make it through after it’s been turned in a different direction. At OE they’re using a tub vibrator to shake their sieve stack in 30-sec. bursts, which I guess is as good a way of doing it as any.

I don’t expect to take the next step and, say, start dabbling in laser diffractometry, but I occasionally look at this thread and marvel at how much further people have gone down the particle size rabbit hole. Then I go make an unsieved coffee and savor its delicious imperfection. 

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