Popper PID profiles, just met the learning curve

Hi folks, apologies in advance for the long post.

I have been roasting in various poppers for a year or so, but just
managed to get a temperature controller in place recently. I have
always like my results in the past, but must say I am really amazed at
how much better my results have been with some basic temperature
management.

I'm using a PII with both coils working together and the fan running
off a transformer, with a K-type bead thermocouple placed high in the
bean mass, and I roast 180grams at a time, based on what the fan
supports. To try to keep the variables down and actually learn
something useful I have been focusing only on Oromia Coop Harar for
the past month or so. The first time I roasted it I was blown away by
what I would describe as incredibly thick, chocolate (more like
cocoa, really) shots without any bitterness our sourness at all.
Unfortunately that roast was achieved in the pre-controlled popper in
a wildly unstable ambient environment so I have no idea what the
profile was.

But I want those shots again?

On one occasion I was able to come close with a simple straightline
profile from 180-440 over 15 minutes or so, but was unable to repeat
that roast for reasons I don't understand. So I've started
experimenting with a more complicated profile based probably on too
much archive reading and not enough personal experience?

Anyway, the controller I am using now has only 4 ramp segments. I have
another more versatile controller but until I get that hooked up this
is the procedure I have settled on for now:

Add beans, turn on fan, turn on heat, let controller reach setpoint of
240 degrees, hold there for 30 seconds, then initiate this profile:
1 minute to 300 (popper falls slightly behind but catches up early in
next segment)
4 minutes to 350
2 minutes to 400
10 degrees F per minute until desired roast level, then shut off heat
and let fan cool to 110.

This weekend I roasted two batches. Unfortunately I entered a target
of 460 for the first ramp by mistake and the beans got well over 300
before I could fix it. I figured the roast was garbage but let them
come back down to 240 and carried on anyway, what the heck right? I
cut it off just into second at 440F and labeled the bag "Harar 440
BAD." Profile must have looked like a view of the grand tetons.

The second batch followed the profile above just fine, and I cut it
off at 438 and labeled the bag "Harar 438 GOOD." Second crack was
somewhat more pronounced this time.

After two days of rest I tried them both today, and was pleasantly
surprised to find that the results were reasonably good - but only
with the "BAD" batch! The "GOOD" batch, on the other hand, was both
bad and ugly. The flavor I was looking for is buried in there
somewhere, but utterly dominated by other flavors I can't describe
other than to call the overall effect "carbony."

Does this make sense? Could that early temperature excursion actually
have improved anything? Can 2 degrees difference in final temperature
be profoundly significant? I would really like to understand what
happened, and how I might go about improving my procedure. Any
thoughts appreciated.

Thanks very much,
Paul
.

Relevant Pages

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