Re: Get "MET" it pays...

I agree with Ken's post, but need to add a bit of Zennish, soft-focus,
elaboration.

For the begining homeroaster, that "ultimate arbiter" of taste is every
bit as loosey-goosey a standard as the "correct" resting period or
pounds of tamp. Cupping knowledge (the ability to taste what's there
and know the taste you are tasting?) and the techniques of roasting are
iterative, reflexive, and developmental; in other words, today's BS has
a way of morphing into tomorrow's useful information. I also believe
that cupping knowledge is the weakest link in the quest for good
espresso, and that's why I'm averse to "if-it-feels-good-drink-it"
advice on how to pull shots.

That's also why I was tempted to ask Mr. Eggers :o) for some
background on his formal or informal cupping practices. His detailed
posts, IMO, seemed to be overreaching in his quest for technical
answers that he could apply directly to his shot pulling. This may be
close to Ken's point about Lin's post below.

Finally,although I do confine my roasting parameters to the basics, my
basics are richly informed by the work of the Schulmans, Staubs, and
others, even if I can't speak confidently or even correctly about
particular reactions taking place at any moment. By comparison, I
think my superficial knowledge of music theory contributes to my guitar
playing experience even though I can't parse out how (or if) it makes
my music better; my knowledge of psychology helped me better negotiate
my parenting even though I can't say it made me a wiser dad, and the
list goes on.

So Lin concludes with "Hope that helps." and I have to say, "No, didn't
help a bit; but some day it might."

Martin

Ken Fox wrote:
Thanks for your explanation.

This is obviously a very complicated topic. Most of those posting on this
thread are home roasters using a lot of different types of "roasters,"
everything (literally) from a dog dish with a handheld heatgun to a small
home air roaster to a barbecue grill with a fabricated drum. Temperature
measurements are taken in widely different locations with varying types of
measurement devices.

My opinion is that most will find the following information interesting but
not really usable in their day to day roasting, where I think they would be
better off following a few basic rules (such as not letting temperatures
stay flat or fall during the roasting process) and taking note of when
audible signs of progress (e.g. the cracks) begin and end. Heat input can
be varied in order to attain roast levels within X period of time. Tasting
should be the ultimate arbiter and what works best can be repeated and made
standard. Of course, this is how it has always been done and for the home
roaster I don't think most will be able to use the terminology given below
in a way that will improve their roasting. But, I could be wrong:-)

ken


<nzlinus@xxxxxxxxx> wrote in message
news:1150811943.057199.82350@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Johnny wrote:
"Erik Groomer" <ViridianCoffee@xxxxxxxxx> wrote in message
news:1150767594.451931.166930@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Johnny wrote:

<snip />
Perhaps it is that the BRR is a stage in the process, whereas MET would
seem to be an end point ET.
You could do 401-424 on the way there.

Pretty much...

Hi All...

I felt like it was time to de-lurk and help shed some light on the
Agtron process. I've been to Carl's class and roasted on a 30lb San
Franciscan using an Agtron PID system for a couple of years, and also
kept some time/temp log info during that time - not that I kept any of
it, of course. I don't recall ever being asked to keep anything
confidential, so here's the deal as *I've* found it to be - when I've
questioned Carl on the matter, he was adamant that it was more complex
- and it might possible be... it just didn't seem that way to me.
There's a few more calculations involved - in determining the charge
weight for a particular bean, and determining the crossover (Transition
temp - TT - see below) between stages 2 and 3 below - based on bean
density (for TT) and burner efficiency (for charge weight) due to
variable atmospheric conditions, but I'll leave that out as being a
little beyond the scope of home-roasting.

The roast is essentially broken into 3 (really 2) phases - 1. the drop
(early roast), 2. BRR set point, 3. MET set point. Note that there is
another temp variable in here - the Transition Temp (TT) - which is
calculated from bean density, and is generally in the range 275 ±10 F
- which is measured from *bean* temp, and seems to provide the point at
which the system flips between it's two control states. (Carl states
that it's not a simple control state and that the ET control temp is
ramped up rather than being a set point control.)

Initial conditions: ET = MET

1. (t = 0 - ~2.5 mins) The beans are dropped and the ET begins to drop.
The burners are pretty much full on while the ET begins to drop, until
the mystical TT is reached at which point the control temp flips from
MET to BRR, and the burners go off until ET has dropped below BRR. The
time this takes is presumably dependent on the thermal mass of the
system.

2. (t = ~2.5 - ~9 mins(from memory)) At this point the burners begin to
cycle again while the system seems to try to control the ET at BRR
temp. In reality, the ET ramps up to the BRR, achieving a steady
ET=BRR state at around 6 or 7 (maybe 8) minutes. This continues until
*bean* temp reaches TT, and the control temp flips back up to MET temp.

3. (t = ~9 - drop) Again, ET and Bean Temp ramp up while the system
tries to raise the ET again. ET = MET is achieved again at around 13
or so minutes, and stays steady while bean temp continues to ramp up
towards drop temp.

Those times are completely from memory - I haven't roasted commercially
for a while - so don't take them as absolutes. I just wanted to give a
better overall impression of the way the system works and how BRR and
MET relate to the Agtron roast process.

My take is that the BRR control point is conducive to caramelization
reactions (Maillards ?) and minimization of Trigonellic acid, while the
MET control point kicks in around the time (or slightly before) the
beans start exotherming due to sugar polymerization reactions, which
keeps more short(er)-chain sugars, which are presumably desirable.

As an aside, I think Carl has done a lot of useful work, and
whether/how he chooses to disseminate his findings is up to him. I
don't think he's FoS, as suggested by another poster.

Hope that helps.
Lin.

.

Relevant Pages

  • Re: Get "MET" it pays...
    ... another temp variable in here - the Transition Temp - which is ... calculated from bean density, and is generally in the range 275 ±10 F ... which the system flips between it's two control states. ... MET to BRR, and the burners go off until ET has dropped below BRR. ...
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  • Re: Get "MET" it pays...
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