Tweener roasts

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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Postby Almico » Jul 13, 2019, 4:31 pm

I've been suspecting a particular roasting anomaly for a while and think I've narrowed down the issue.

This is a typical medium roast profile:


I actually use this as a template for medium roast Central and South Americas. I let it go to 400* for a full medium, or drop sooner for a lighter roast. When I get lazy I'll use this profile and modify my heat settings when I want something different. I can tell by the BT curve whether I'm getting to 400* in 25% post 1C or 20%.

Anyway...being in the biz, I have the "luxury" of roasting the same coffees over and over again under lots of conditions. I am able to formulate a good game plan to achieve most roasting goals.

The other day I roasted 8# of a fantastic Colombia Yellow Bourbon that I've been working with for a few months. I have roasted dozens of batches, most on the light side. I use the above profile and turn down the heat a bit more before 1C and drop around 18% at 390*. It makes for a very bright and juicy drip. I will also take this coffee to 400* and drop around 20% for a more carmelly flavor profile. It is great both ways.

So I bagged up a few bags for retail and brought in a bucket for brewing at the bar. As my norm, I always taste the first cup of every roast. This time I was stunned to find it almost undrinkable. I tried grinding finer...much worse. I went all the way up to the coarsest setting on my R120 and it was drinkable, but not sweet and still had a hint of methyl alcohol.

Unfortunately, I did not save this roast profile, but I do remember it. I got distracted and did not turn down the pre-1C heat from 30% to 20% where I should have and the BT ran away a little. Not badly, no big RoR hump, but I dropped at the in-between temp of 395* in 20% DTR. I did not think anything of it. It was certainly within the range of what had previously produced great coffee.

But something developed at 395* that was not there at 390 or 400 that was so offensive I dumped 4# of brew coffee and tossed 4 bags in the garbage.

I have not read anything about this phenomenon as yet. I believe Jim touched on something similar in one of the light roast threads.

Anybody have a similar experience?
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Postby EddyQ » Jul 13, 2019, 10:29 pm

I cannot say I ever dumped a batch. But I also don't roast much volume for customers and have avenues for sub-part coffee that mitigate the trash.

Is it possible the beans got a bit scorched? Do they show signs of tipping? A profile like that should produce some nice sweetness if the coffee has some. But you said heat was left on a bit too long when MET and drum temps are likely the hottest.

Other things that seldom amaze me is how off flavors can be just after roast. The next day or so can be so drastic that I wouldn't think it was the same roast. But many beans don't do this. Often right after roast, most beans lack some sweetness and can have a baked and/or more roasty taste. But with rest, these flavors often go away leaving some wonderful sweetness and flavors with no baked flavors. But I recon you have experience that way tops me with this sort of thing. But I thought I would caution you with the chance some rare bean may be messing with you.

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Postby Almico » Jul 14, 2019, 1:24 am

That's the weird thing; nothing drastic changed from my normal roasts.

I roasted a replacement batch tonight. I took this one all the way to 400* for my "medium" roast. (It's actually closer to light than medium on the Agtron scale)

I've gotten pretty good at controlling my roaster. As you can see, I'm 0.7*, total from dry to drop, off my template roast. It's hard to see, but there is a pattern roast behind the current roast.


Even with my evil Sumatra bean, and all that goes on with that roast plan, I'm pretty on the money for replicating roasts:


So this is not a matter of tipping or scorching. It's about a foul chemical compound being non-existant at 390* and 400* drop temp, but present in spades at 395*. All roasts dropped at the same time and with the same 20% development time,


Postby crunchybean » Jul 14, 2019, 8:37 am

The amazing world of chemistry.

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Postby Almico » Jul 14, 2019, 12:54 pm

I brewed a pot of the above roast this morning and it was delicious. I will try the 390* roast next time.

I feel I should try and duplicate the funky roast, but in order to remove as many variables as possible, I would need to use 8# of coffee. I hate to do that. Maybe it's time to fire up the Cormorant and try a few test roasts and see what I can figure out.


Postby N3Roaster » Jul 14, 2019, 3:19 pm

I've been talking about this kind of dramatic sensory step change in classes recently and touched on that a bit in the May 13 episode of Coffee and Code (though in this case picking on a raw coffee flavor that's become depressingly common). Some of these, like that raw coffee flavor are highly correlated to end temperature and largely universal regardless of coffee or roasting plan. Those are fantastic to find because once you get good at picking the flavors out in the cup they become reliable places to compare when attempting to match a roasting plan across different machines (I've recently done some work replicating my pre-purchase sample roast from the Diedrich IR-1 to an IKAWA Pro V3 and those sensory cues have been highly useful in fine-tuning that). Others such as the one you've found here, tend to be present only on some coffees and those coffees can often be great at other end points. One of the many reasons I still do a progressive roasting exercise with every coffee that comes in is precisely to find and avoid this sort of unpleasant surprise.
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