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Topic: Fresh Roast load size (was Re: +Freshroast Plus -- Aargh, help) (2 msgs / 149 lines)
1) From: Kevin DuPre
My FR came from Coffee Bean Corral who advised
ignoring the "fill line" and instead sent a 43cc scoop
which I use 2 of leveled off (86 cc batch size which
averages around 60 g per batch - typical green batch
density of around .698 to .710 g/cc) On the FR this
gives 1st crack around 2:10 - 2:30 with the vents
closed (I haven't noticed a lot of difference with the
vents open), and a rolling 2nd around 3:10 - 3:40
depending on the beans. Add another 0-20 seconds for
roast development beyond 2nd crack and 2 minutes for
cooling gives about a 5-6 minute profile. Indian
Monsooned Malabar seems to take a lot longer.
I've found the following relationship between batch
size, density-altitude, airflow, roasting temperature
and roast duration from experimental data:
INCREASE batch size (or INCREASE Density-Altitude),
DECREASES air flow,
INCREASES roasting temperature,
DECREASES roast duration.
It seems that as you increase the batch size or
density-altitude, the bean mass increases the back
pressure (slowing down the air flow), allowing the
heater to run hotter which increases the roasting
temperature decreasing the roast duration. Change any
one of the above variables (bean mass you can control,
and density altitude is a given, unless you are in an
environment where you can control atmospheric pressure
or ambient temperature) in the same or opposite
direction, and the others will change correspondingly.
Other FLUID-BED roasters may behave differently, but
this is the relationship I've documented and observed
with the original Fresh Roast and which I assume will
hold in a columnar, air-fed-from-the-bottom type of
roaster such as the FR/FR+. I have no reason to
believe that the FR+ will differ in the above
observations from the FR.
I know my roasting times above are considered SHORT.
I'm not saying this is right for you, but I like the
way the coffee tastes (brighter) at this profile.  If
I want to mellow it out some, I've modified my roaster
with a footswitch operated relay which interrupts the
heater current when the momentary footswitch is
depressed. I typically will alternately depress and
release the footswitch to hold the bean mass
temperature fairly constant between 1st and 2nd crack
to lengthen the profile some before letting it run out
to finish.  You can also do this by alternating the
timer dial between heating and cooling while
monitoring the bean mass/chamber temperature with one
of the small probe thermometers sold by Tom and Maria
dropped in a small hole drilled around the center of
the top (slightly off center since there is a pin and
screen retaining clip in the center of the lid).  
In order to get the probe at the right level in the
chamber, I sawed off the top 1/2 inch of the plastic
storage sheath the thermometer came in and slid this
over the probe shaft with a one-way retaining clip to
keep it in place. The assembly is then dropped into
the hole you drill into the top (same diameter as the
shaft, but be careful when drilling to not use too
much pressure - the top is bakelite and is a brittle
material so you'll have to drill slowly). This sets it
in the right level of the roasting, growing bean mass
during roasting cycle.
What I should do if I don't want to control the
temperature between alternate heating and cooling is
to decrease my bean volume, but this means more
batches to get the same volume in a roasting session.
Go too low in the batch however (I've found less than
about 45-50 grams), and you will stall the roast, all
other things (such as ambient roast area temperature
and atmospheric pressure, which affects
density-altitude) being equal.  My ambient
temperatures are somewhere between 65 and 75 degrees
with a density-altitude varying between 950 and 2000
feet depending on atmospheric pressure and ambient
temperature.  If you are at mountain altitudes (2000
feet and greater) or experience a wide swing in
density altitude which makes your apparent altitude
much higher, your roast times will be shorter(due to
decreased air density and resulting decrease in
airflow with its corresponding effects in the above
relationship)
If you are not familiar with Density-Altitude, it is a
measure of APPARENT altitude depending primarily on
Ambient Temperature, Atmospheric Pressure, and Actual
Altitude of the area you are roasting in.  I use a
pilot's calculator for the PalmOS ($5.00) which you
can download athttp://www.tinkershop.net/gobzi.htmif
you have a Palm.
A varying density altitude (from one roast-session to
the next), which affects the efficiency of gas-fired
roasters, seems, from my observations and recorded
data, to have an affect on roasting time with a
electric-fired fluid-bed roaster such as the FR.  A
higher DA will have a similar effect as an increased
batch size (because there is less air density at the
higher apparent altitude to float the bean mass which
affects the relationship above) shortening the roast
time, all other things being held constant, in my
experience. 
Probably more than you needed to know, but after
100-150 batches through my FR, I've learned a few
things along the way.
Regards,
Kevin 
<Snip>
=====
--
Kevin DuPre
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2) From: EskWIRED
<Snip>
This is true, but only up to a point.  Beyond that, more beans = more time.
Try it.
<Snip>
It depends on more factors.  If you hit the upper limit of BTUs for your
heater coils, then more beans will give a longer roast.  However, if your
airflow is insufficient, you can end up with uneven roasts, unless you stall
the beans at just under first-crack temperature.  Try it.
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