Coffee solubility seems to be a topic of increased interest as of late. I think the obvious application is espresso. Truly “overextracting” espresso - achieving extraction yields north of 22% - is extremely hard. Even extracting espresso at 18-19% is often difficult, and Roburs are essentially physically incapable of surpassing ~20% extraction in espresso. (Seriously.)





So we have tools we’ve developed to combat this - modal grinders (EKs, unimodal flats rather than bimodal conicals), VST baskets and $200 precisely-machined, flat tampers, longer extractions with gentler preinfusion allowing finer grinds, hotter water, less charred roasts that don’t fall apart at 20% extraction… etc. In an ideal world, our espresso roasts work well as drip coffee and our drip roasts make pleasant espresso. (Though perhaps they aren’t quite the same.)



The ideal is lightly-roasted espresso that’s just as extractable as Illy. Espresso should be tasty at 20% extraction. And it shouldn’t require tons of equipment to eke out a correct extraction - just a flat burr grinder, water at 200 F at the grouphead, a flat tamper with correct sizing, a shot at 2:1 or longer, and a competent barista.



Solubility isn’t just about espresso, though. Solubility is important in brew roasts for a few reasons (1) an easily-extracted brew roast can be pulled as espresso (see: heart), (2) an easily-extracted brew roast will be better-extracted by customers, meaning they might get closer to the 20-21% that I think is common in good shops, and (3) to some extent, a roast that isn’t fully-extractable isn’t fully-developed. This is a point that Scott Rao makes in his Roaster’s Companion and it’s an interesting one, even if I’m not fully convinced that it’s correct. (Other notable coffee nerds I’ve heard suggest this include Perger and Kaminsky.)



So I’ll be investigating solubility in the context of espresso. This isn’t because I think that solubility is only relevant in the context of espresso but rather because espresso, when extracted to the correct range, makes solubility issues in a roast glaringly obvious.

So let’s delve into it…

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My home espresso setup is a CC1 (with a VST 15g basket) fed by an HG One or EK43. The HG One is a large conical burr grinder, and the CC1 non-preinfusing (it claims it preinfuses but just turns the pump on and off), PID-equipped espresso machine and is reasonably characteristic of what a third-wave wholesale account would be using. The EK is obviously flat-burred, produces a more modal particle size, extracts higher, and can get away with pulling lighter-roasted coffees as espresso. But it struggles to pull much tighter than ~40% brew ratio. (So around a 35-40g shot in 24-28s.) So both grinders are useful.

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The first step was to pull some of my brew roasts and examine the results. I wanted to look at two approaches to improving development in light roasts. The first is characteristic of a lot of Nordic roasters - stretching out the drying interval to help get the bean up to temperature before applying lots of heat quickly in ramp and development. This is a strategy I’ve found effective for achieving very light drop temperatures and weight loss percentages in brewed coffee.

The second approach is one endorsed by Rao and which has gotten more attention lately. Here I’m charging very hot, applying quite a bit of heat early, and slowing down the roast at the end. I was working with Sweet Maria’s Karongi Gitesi Rwanda.



Full-resolution profiles, be sure to match with numbers because they uploaded out of order: http://imgur.com/a/1KEpi







From cupping (1:18, 203 F, 1.3 TDS, 20% extraction), profile one above is more sweet, clean, and tartaric, plus a bit of citrus. Two focuses more on citrus and has a bit more caramel.

From V60 brewing (1:17, 203 F), profile one is more sweet and delicate, more crisp. Profile two is fuller and more caramelized.I preferred profile one as brewed coffee due to the ripe fruit flavors, cleanliness, and clarity.

Espresso, 2/18/2015, 7 days post. HG One into CC1, VST 15 basket

Roast 1 above, the slow-start profile did not pull well. The first shot was 15g in, 34g out in 30 seconds, the shot was salty and peanutty (suggesting somewhat incomplete development). Longer time shots got a bit medicinal.

Roast 2 above pulled pretty decently. Pulling 35g in 30s from a 15.0 g dose resulted in a pleasantly syrupy, raisiny shot. There was no peanut or other underdeveloped character to be found.

So here we have some initial support for aggressive charge temperatures as encouraging even bean development. However, I didn’t consider this adequate because (1) these are probably just too light for espresso use and (2) the slow-start profile was lighter than the hot-charge profile.

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Realistically, I didn’t expect finishes this light to work well as espresso, at least on my setup. I roasted two more batches with the same two approaches but with drop temperatures a couple degrees hotter but still in the city range. In this case, the slow-start approach actually turned out more developed in terms of weight loss, so we don’t have depth of roast as a confound. If the deeper slow-start roast proves less extractable than the lighter hot-charge roast, that would strongly suggest that hot charges are a better strategy for improving espresso solubility.





Again, I pulled these shots seven days out, in a VST 15g basket, ~200F at the grouphead. I used an EK43 this time, dosing 16.0 g and grinding at 1.3. For both roasts, I got 50 +/- 3g in 23-25 seconds. I wanted to extract aggressively to give the slow-start profile a chance at success.



With the slower-start profile, I did really enjoy its profound sweetness and red fruit. However, there was a certain musky, somewhat underdeveloped character, not enough to ruin the shot or enough enough to disturb a pour-over brew, but present.

With the aggressive charge profile, flow was slightly slower. The shot was fuller, riper, more buttery, and completely free of off-flavors (i.e. muskiness, muted peanut-salty-savory character). The shot was slightly less fruited and perhaps slightly less sweet. Both my friend and I agreed that the second shot was significantly better.

I also roasted a batch of Sweet Maria’s Nano Challa washed Ethiopian coffee. For this one, I dropped a couple degrees hotter yet, probably edging into city+ territory, but still light for an espresso-centric roast. The results from this agreed with my previous statements - a hot charge helped facilitate proper development in a light espresso-centric roast. A similar story held true for a couple roasts of a coffee from the Yetatebe cooperative in Guji, Ethiopia.

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So what does this mean? Well, I think it’s pretty clear that using hot charges is a superior strategy vs. longer drying times for achieving solubility in espresso roasts. And I think it’s already clear that the drying phase is a superior choice to stretch than ramp or development. Extended development will give you excessive caramels and muted sweetness and extended ramp will produce meaty, savory, popcorn-like flavors. So stretching out the roast to improve development is only useful to some extent, and is far over-used. In particular, stretching out the development phase to better develop the inside of a coffee bean has rapidly diminishing returns past a certain point - certainly past 25% development ratio. (In this sense, the name’s a bit of a misnomer… but then again, so is the term “drying phase.”) This is a point that Rao makes in his Roaster’s Companion, and I think it’s a point worth repeating. (Just to be clear, I’m not saying that stretching out a roast is never productive, in terms of flavor - it often is - but it generally isn’t very effective at increasing solubility.)

As far as brew roasts are concerned, I’m not entirely sure where I stand. I think solubility is an extremely important concern for a commercial roaster. So heart is being reasonable by roasting slightly darker than they used to for their drip roasts. But on the other hand, I have the utmost respect for someone like Tim Wendelboe who puts out an immacuulate, ultra-light roast that requires great equipment, brewing, and water, but, when brewed properly, is incredible.