Dark Outer Bean Color

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
maccompatible

#1: Post by maccompatible » Dec 04, 2019, 4:27 am

I've made a lot of progress on my Behmor 1600+, somewhat unconventionally. I haven't modded my unit, but I preheat just below auto-shutoff on the 1lb setting, load in the beans, and let it fly on P5. This usually means loading a batch just before the fans kick on. I like doing it this way because this gives nearly constant airflow during the roast instead of no airflow until midway through the roast, and allows me to simply decrease the heat as the roast proceeds instead of worrying about the afterburner interfering mid-roast.
I am a bit concerned with some of my roasts, though. Some of the washed coffees, especially those with predominant "sweet" tasting notes and smaller bean size, tend to be much darker than the rest of the data would lead me to believe. For instance, my last roast was 12.7% moisture loss. I used P5 until 5 minutes in, 1C began at 6:20, I cut to P3 at 6:35, there was steady crack until 7:50, and I dropped at 8:15. By my calculation, that's 23% development time ratio. Of course, there's no usable temperature data, but the beans appear visually darker than I'd expect.

So my questions: is this even a problem? (these roasts rarely taste ashy, and usually do taste sweet and fruity/floral like I hope for) Would a professional drum roaster do the same thing? Am I applying too much heat at any point in the roast?
If I had a reliable BT probe, I feel like I could probably figure this out for myself, but any information you could provide I'd appreciate!

Thanks in advance.
"Wait. People drink coffee just for the caffeine??"
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mkane

#2: Post by mkane » Dec 04, 2019, 8:39 am

Bean color should tell the whole story. An expert could probably take a look at your beans and have a good idea what DT was.

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Almico
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#3: Post by Almico » Dec 04, 2019, 11:53 am

At first blush you are charging hot with lot's of air. That will "cook" a roast quickly. But since your roast was fairly short, you might not be getting the typical divots and tipping associated with roasting too quickly. Slice open a few beans and see if the outer is considerably darker than the inner.

FWIW, on my very light roasts I still get 14% moisture loss. Not sure how you are getting dark looking coffee with <13%.

maccompatible

#4: Post by maccompatible » Dec 04, 2019, 1:55 pm

Almico wrote:Not sure how you are getting dark looking coffee with <13%.
That's my main confusion, which is why I made this post. :lol:
Almico wrote:Slice open a few beans and see if the outer is considerably darker than the inner.
Nope. They look pretty much the same all the way in.
Almico wrote:At first blush you are charging hot with lot's of air. That will "cook" a roast quickly.
So perhaps I've gone too far? Of the three things I do to speed up drying on the Behmor (1. high preheat, 2. max initial heat, 3. loading just before the fans), which should I try backing off on? I've read in many posts on this forum that constant airflow is ideal, so perhaps I should back off on the amount of initial heat I give the roast? Maybe 2 minutes of maximum heat instead of 4 or 5?
"Wait. People drink coffee just for the caffeine??"
LMWDP #628

maccompatible

#5: Post by maccompatible » Dec 04, 2019, 2:45 pm

Almico wrote:At first blush you are charging hot with lot's of air. That will "cook" a roast quickly. But since your roast was fairly short, you might not be getting the typical divots and tipping associated with roasting too quickly.
I just tried another batch.
155.6g in, 136.4g out, 12.3% loss. Preheated to 325, loaded in with 10:30 left on the timer (when the fans and AB kick on).
Gave it 2 minutes on P5. Some yellowing at 4 minutes in, and no crack until around 8 minutes. I cut to P3 at 8:30, and left it there until 10. So 20% DTR, dark looking coffee, but very low weight loss again :? Also, the crack seemed very sluggish this time, so I think cutting some of the extra heat off the beginning hurt this batch's momentum.

So it seems the heat setting at the beginning isn't the issue. What else could it be? Do you think I'd be better off with a lower charge temperature? Loading in BEFORE the fans come on? Both?
"Wait. People drink coffee just for the caffeine??"
LMWDP #628

N3Roaster

#6: Post by N3Roaster » Dec 04, 2019, 6:48 pm

My guess on this would be low moisture content on the raw coffee. In recent years I've spoken with several roasters who have found very nice coffees that came in below the old moisture content spec for specialty green grading and storage conditions that are not ideal can also cause a green coffee to have further drying before you roast it. If you're used to getting coffees at the higher end of that moisture content range and suddenly start getting coffees at the low or even a bit under range, that can cause the disconnect between color and mass loss compared with what you're used to. As for if it's a problem, do you enjoy the flavor you're getting? If yes, it's not a problem, and if the problem is related to green coffee moisture, then yes, a commercial drum roaster will exhibit the same behavior.
Neal

maccompatible

#7: Post by maccompatible » Dec 04, 2019, 9:36 pm

N3Roaster wrote:My guess on this would be low moisture content on the raw coffee... If you're used to getting coffees at the higher end of that moisture content range and suddenly start getting coffees at the low or even a bit under range, that can cause the disconnect between color and mass loss compared with what you're used to.
Oh, interesting. I hadn't considered that. That would definitely make sense.
N3Roaster wrote:As for if it's a problem, do you enjoy the flavor you're getting? If yes, it's not a problem, and if the problem is related to green coffee moisture, then yes, a commercial drum roaster will exhibit the same behavior.
That's why I'm so confused. What I'm getting tastes good to me, so I'm just wondering why my numbers seem so off.
For the sake of experimentation and improvement, I'll probably keep playing with this green coffee, as I bought 5 pounds of it and only roast a 1/3 lb batch at a time in the Behmor.
"Wait. People drink coffee just for the caffeine??"
LMWDP #628