at odds with unevenness

I very recently acquired Scott Rao’s new book, Everything But Espresso, and having turned through its pages a couple of times I am struck by what a timely piece it is. I agree wholeheartedly with the spirit of the book, and to a large extent the details. The prominence Scott places on correct extraction, brew ratios, even extraction, consistency of methodologies, are all bankable principles – and I will concur with James’ verdict, it is an essential acquisition.

Scott also raises for me, some thought provoking though more debatable topics, such as coffee bed geometry, and the merits of post brew inspection of said bed, and brew diagnosis. The tenant of his point is that there are certain actions you can take to affect the end bed architecture, that will improve the evenness of drawdown, which will impact the quality of that portion of the brew (though not necessarily making up for problems with other parts of the brew).

It is hard to argue with his logic.

This train of thought brought me back to rewatching THAT video, and to rereading THAT divisive but very interesting thread on Coffeed.

One of the points that comes up was whether the grinds at the bottom of the cone were overextracted relative to the grinds at the top of the cone. Though this seems self-evident, especially when a lot of the top grinds are out of the equation at an early stage, has anyone shown real evidence of this?

Methodology

To show some real evidence of this, using an Uber Boiler set to 92C I prepared 8 pour over brews (actually 9 as there was 1 duplicated with a Buono kettle). Using a Chemex, a V60, a Donut dripper, and a Melitta dripper, I prepared 2 500g (brew water weight) / 30g (ground coffee weight) brews with each, the first a continuous center pour with no manual agitation (ala the SqM video), the second using a series of small pours with stirring at the beginning and end (ala the book).

[xr_video id=”387b1ceb70e54b05b027ebad710695cc” size=”md” title=”false” viewOnXR=”false” width=700]

When these brews were completed I immediately retrieved used grinds from the filter papers, split approximately in half, resulting in two samples from each brew (a total of 16 samples) – representing the top grinds and the bottom grinds.

These were spread out on ceramic saucers and dried in a 50C oven for 30mins.

6g samples of dried grinds were weighed, and rebrewed with 100g of boiling water for 10 minutes to extract remaining solubles.

Beverage strength of these rebrews was determined with a Reichert R2mini Refractometer (aka the Extract Mojo refractometer).

For illustration purposes, soluble yields are normalized (ie graphs represent the ratio of top to bottom – with the higher yielding sample always being one).

Comments on the methodology

• Apart from the V60 center pour / no agitation test, which was performed twice, all of these are n=1, and as such are not statistically significant, or to be considered definitive. I would encourage others to replicate these experiments.
• 92C was chosen somewhat arbitrarily, as it was the temperature being used by 3FE to brew Hasbean’s Finca La Fany via Chemex. This was the coffee used for the experiment.
• Ideally a higher number of samples would be taken, as I am certain extraction imbalances are likely to be gradiential rather than binary.
• Boiling water was used without any regard for brewing convention and taste, instead merely to readily extract a large proportion of the remaining solubles.

Results

I will present the results on a brewer by brewer basis.

I expected the V60 brew to deliver a relatively even extraction, due to the perception that substantial brew water leaves the brew via the sides as well as the bottom, also it seemed to me plausible that the center pour no agitation method could produce an even extraction if the brew water path was through an equidistant bed of coffee along all surfaces.

My results indicated (and this one was done twice – and the results agreed) that the V60 with this methodology produced the greatest discrepancy between top and bottom. I retrieved 4 times more solubles from the grinds at the top of the cone, than the grinds at the bottom of the cone, when rebrewed.

Using the stirring methodology, greatly improved this, to the point that I retrieved only marginally more solubles from the top grinds. The ratio here was 4:3, instead of 4:1, still uneven but greatly improved.

I expected the Chemex on the other hand to produce the most uneven results, with all of the brew water channeling through the point of the cone, with little side drainage.

The first Chemex brew (similar to James’ video) produced a brew greatly more even than the same V60 brew, while not as good as the stirred V60 brew. In the case of the Chemex, I found the stirring I performed to negatively impact the evenness of the extraction.

The Melitta cone, was probably the star performer on the day, producing an unstirred brew slightly more even than the Chemex brew, and only slightly less even than the sitrred V60. In the stirred Melitta brew, however, the two samples were almost indistinguishable, and certainly within the margin of error of the Reichert mini refractometer, and my experimental methodology.

The Donut, a brewer I used a lot prior to dropping it on the floor and breaking it produced the most even unstirred brew. Oddly, however, unlike the other 3 brewers it produced a brew in which more was extracted from the top, than the bottom. When stirred, however, it produced a brew slightly less even, though markedly different in that now the bottom was more extracted.

Discussion

I would stress that these are n=1 findings (apart from in one instance), and should not be used to definitively call one brewer superior to another. What I would confidently take from this, perhaps, is that cone shaped brew basket geometry produces and uneven extraction in general, and that stirring can impact both positively or negatively the end result.

The V60, which I will confess has been my brewer of choice of late, on two separate brews, one with the Uber and one with a Buono kettle (at home) produced the most uneven extractions. Certainly, in the process of preparing all the brews on 3FE’s Uber, and tasting small samples of each, I remarked that the V60 brew tasted the worst, jangly, hollow even. This would not have been in keeping with my general opinion on the device.

The Donut, I find quite intriguing, as its geometry is the most unique (in this group). It could be most accurately called a truncated cone, or thought of as somewhere between a cone and a cylinder. Some say it is a pointless brewer (ahem), and I would agree with that – as such the bottleneck effect on the path of the brew water would appear to be less dramatic than any of the other brewers (although the choice of one central hole in favour of several dispersed  perhaps diminishes this). There are so many possible factors that might  explain the results I observed, with this brewer that for me to single some out would be close to idle speculation. So I won’t.

The humble Melitta cone held its own on the numbers front at least, and when stirred produced the most even extraction. Its hard for me to say why I hold little affection for the Melitta cone, perhaps not least because I cannot seem to get filter papers for it that don’t taste like sawdust. Certainly though in terms of geometry it would seem to stand a better chance than the cone shaped V60 or Chemex beds at producing an even extraction.

The question, which naturally proposes itself amidst all of this is whether an even extraction is truly the most desirable outcome of brewing some coffee. Peter Giuliano’s steak analogy on the Coffeed thread, suggests an alternative is possible. While the cooking of steak probably has more in common with the roasting of coffee than the brewing of it, and I don’t think anyone advocates uneven roasting, Peter’s point is a fair and reasonable one.

Scott Rao somewhat addresses this in his book, suggesting that because grinders produce a wide range of particle sizes anyway, that the complexity of multiple extraction levels will always be achieved, even in an otherwise “even brew”. It is unclear if Scott is merely eliminating the complexity argument as a potential criticism for his proposed methodologies, or if he believes the complexity of an extraction spectrum is desirable.

For my part, having compared a lot of brews made with sieved grinds and non-sieved grinds, I remain in favour of evenly extracted brews made from grinds all of the same size (or as narrow a size distribution as possible). I think we have acquired the taste for what our grinders can produce, and somewhat for what our brewers can produce. This is what coffee should taste like in our mind, it is the baseline from which we judge everything. We have , I propose, acquired a taste for unevenness of varying degrees. I would propose an experiment where non-coffee drinkers are given a preference test to determine whether they would choose the sifted brew over the non-sifted kind. My money would be on the former.

But I digress.

My bottom line is that I see no rational reason why we should choose an uneven extraction. Let’s not get hung up on defending our corner, our methodologies, by proclaiming unevenness “a feature”, whether due to grinder, or brewer.

It’s not a feature, it’s a bug.