The double hump

November 8th, 2010

This post has come out of an email conversation between Andy Schecter, Scott Rao and myself. Scott had originally considered posting this as a comment on the Brewing Outside of Gold Cup post, but I thought it was too interesting to take the chance of being missed by people who might find it very interesting.

The timing seemed excellent after my last post on Cupping and French Press – for reasons that I hope will make sense once you read it.


Yes, there are three situations that come to mind where I have preferred coffee extractions that were “outside the box” (my usual box is 19-20%)

Situations in which different areas of the coffee bed were extracted to very different degrees (i.e. the strange ways most companies seem to make v60’s, some clover extractions (also usually absurd technique), and, in fact, espresso (it is impossible to get a uniform extraction from espresso.) I know you said you weren’t referring to these, but I would like to point them out. These extractions generally have tasted best below 19%.

There is something I call the “double hump”. These comments assume extraction (not water) temperature between 198-201F (92-94C) and the use of a commercial flat burr grinder with relatively sharp burrs. I would not generalize about extractions at different temperatures or made with different-quality grinders):

<15%: I have very little experience, or at least have had very few enjoyable experiences below 15% extraction.

15-16%: This is the “little hump”. I’ve often found these extractions to be cirtusy and juicy, with a more delicate acidity than that of higher extractions. To me they’re the coffee equivalent of Beaujolais Nouveau. They’re also more aromatic (perhaps simply due to the higher grounds: water ratio… aromatics extract almost instantly, and the aromatic profile of a coffee correlates far more with extraction temperature than it does with solubles extraction level.). Using a higher grounds:water ratio will inevitably result in more concentrated aroma.

If a relatively uniform extraction, 16-18% is a bit of a dead zone: less fruit than either hump, and acidity tends to be flatter. The caramel content of the cup may be higher than at the little hump, but the overall cup is rarely great. Woody and harder flavors often come to the fore at this range.

18-19%: As you creep towards 19%, the presence of bigger, riper fruit and deeper caramel tastes increases. This range can be great or sometimes boring.

19-20%: The “big hump”: This range most often produces the ripest, most pleasing fruit (the type Robert Parket champions in wine) and the most caramels without the presence of appreciable astringency or bitterness.

>20%: As the extraction increases beyond 20% the risk of bitterness and astringency taking over the cup increases exponentially. Some of the best cups of my life were between 20-20.5% but in a café setting I would usually err on the side of caution and aim for closer to 19.5% in order to avoid any creeping astringency.


I’ve had some recent experiences with brand new, very sharp, very large grinder burrs, as well as experiences with roller mills, that have convinced me there can be beautiful flavors in the 21.5-22.5% range without appreciable bitterness or astringency. I would speculate that such high-quality grinds, with minimal very-small and very-large particles, can extract to a higher degree more successfully than can the typical grind quality and particle size distribution most of us use in our cafes everyday. Please note: I do not think that using a Ro-Tap or a fines-separator with a “normal grinder” to produce a narrower particle size distribution can reliably replicate the grind quality of a truly superior roller mill or a machine with very large, flat burrs.

Part of me wants to leave it here and just let people discuss stuff in the comments but I can’t resist a little commentary:

1 – Uneven extractions: This is interesting, and I think a lot of people will jump on this, but it isn’t the most interesting thing for me here. I’d like to avoid the “ExtractMojo can’t gauge the evenness of extraction, and is therefore redundant” argument here please.

2 – The small hump: This is really interesting to me. It is something similar to what I have experienced with brew temp in espresso. If you go a little low it easily turns sour. Drop lower again and its sweetens up but gets quite boring. I’d really like to understand what is causing the dip in quality between 17-18% range. Thoughts and comments on this would be especially welcome.

3 – Grinders: First of all – on this point I am quite jealous, I’d love to play with roller mills and the like. It also brings up my frustrations with the lack of grinder research in the last 50 years.

Thoughts and comments on the above welcome!

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