This past week, I conducted a series of roasts to evaluate the effects of drying interval (that is, time from charge to 300 F bean temp) on flavor. Credit has to be given to Chris Schooley at Sweet Maria’s / Coffee Shrub for his seminal Stretchin’ Out the Roast Series that inspired this. I figured I could hone my palate and perhaps add a bit to the discussion.

I’ll give the experiment details and then start discussing. I’ve brewed up close to a dozen V60’s of these coffees, cupped them twice, and shared them with around a dozen coffee pros, so I think most of these claims are pretty well-supported where possible.

All roasts used Sweet Maria’s Kenya Nyeri Gatomboya AA. I’ve had numerous coffees from the Gatomboya washing station before, and they’ve been lovely. So I knew I was going in with a really pretty, clean, sweet, juicy coffee.

All roasts were to share a rapid ramp from end-of-dry (“EOD”) (~3-3:15) to first crack start (1cs). All roasts were to share a development time of 1:45, since I’ve found that degree of development to produce nicely candied sugars with a long finish in my particular roaster (a Quest M3). This does mean that development as a percentage of roast varied. I thought fixing dev. time was more important than dev. percentage. All roasts shared a fan adjustment of 3.2-6-max. All roasts were dropped at 403 F BT (around 20-25 degrees above 1cs in my roaster, producing a city roast, somewhere in the low 12’s to high 13’s % weight loss).

Now, the variables. Charge temp was adjusted for the 6/5/4 minute drying interval goals. Heat was applied variably during drying as well, obviously.

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Profiles can be viewed in full-resolution here but will also be pasted below for convenience.

Here’s the six minute dry. 1cs was marked a hair late, but ramp did run a couple seconds long and dev. a few seconds short. In any case, pretty much on-target. As a side note, the fact that this type of profile tastes quite pleasant should be a reminder that declining RoR is not strictly necessary, at least not for my palate. A couple beans missed the chute when charging, so I couldn’t calculate % weight loss (%WL).

Here’s the five minute dry. This roast was entirely to-spec. It’s interesting to note that the RoR is essentially linear for the entire roast with a notch at 1c. 13.13% WL

Here’s the final roast, the four minute dry, also to-spec. This achieves a declining RoR, again hitting all targets. 13.32% WL

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I’ll refer to the roasts as (6), (5), and (4) for six-minute, five-minute, and four-minute drying interval respectively.

On my first cupping, the sweetness of (6) immediately stood out, even from the dry aroma, and more obviously upon break and tasting. The roast had primarily tartaric (grape-like) acidity and reminded me of a red jolly rancher. (5) was pleasant and clean and sweet but didn’t blow me away. (4) was the most aggressive with its acidity (intense but also a bit rough), the most citric, and the most full-bodied. (4) also had a noticeable flavor of cacao nib, bitterness on the back of the palate, and a substantial black tea astringency. I attribute these qualities to the high heat early in the roast. In contrast, (6) was exceptionally smooth and free of roast character.

As a 1:17.5, 203F V60, (6) produced aromas of ripe cherry, pineapple, and mandarin orange. Its taste was exceptionally sweet and focused on maraschino cherry along with dark fruits of raisin, plum, and blackcurrant. Its acidity was not exceptionally prominent but was present and there was very little bitterness despite being extracted at >21%.

I also brewed a V60 of (4) with the same parameters. This roast produced brighter, more tropical aromas of pineapple, guava, mango, and meyer lemon. In the mouth, it had more body, more tea-like qualities and astringency. It was highly complex and interesting, but less immediately likeable.

I brewed up each as a V60 for my coworkers. Opinion was split. Four of us preferred (6), three (5), and one (4). (My opinion was that (6) was the clear winner, with (5) and (4) each having strong points.) This consisted of me brewing up V60’s before a shift, and handing them to people to offer opinions, so it wasn’t exactly rigorous and would’ve probably produced less variance if conducted in a more controlled setting.

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Finally, I’ll offer a couple conclusions. All are tentative and should be regarded as such. It is always my suggestion that you go out and roast! And write about it! (And tell me.)

As Schooley noted in his experiment, stretching out the roast at any point reduces acidity. Stretching out drying reduces acidity without adding substantial malty, caramelly, or distillate (tobacco or smoke-like) character. Importantly, I found that extending drying time altered not just the quantity but the quality / variety of acidity. Extended drying reduced citric character and increased / revealed tartaric character. (I can’t say whether this would hold true for other coffees.) My working hypothesis would be that citric acid is less stable at roasting temperatures than tartaric acid.

I found that (5) and (6) were substantially more aromatic than (4). This suggests that very short drying times may offer less aromatics.

Finally, (5) had a linear RoR and produced the least “exciting” cup. It had neither the acidity of (4) nor the sweetness of (6). So perhaps Rao’s assertion about declining RoR has something to it. Perhaps we could amend it to something like “linear RoR produces less complex flavors” or “variance in RoR produces more complexity of flavor” since roast (6), which had, in fact, an increasing RoR at one point, was super sweet and aromatic.

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Up next: adjustments in ramp interval. Expect another post in around a week with results.