Re: Seeking wisdom: air flow control on commercial drum roasters...

In <1141341407.203424.230760@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, on 2 Mar 2006
15:16:47 -0800, webmaster@xxxxxxxxxxxxxxxxxx wrote:

3 factors affect the roast; time, temp and air flow. Air flow is the
HARDEST to reset once you have changed it.

Unless it isn't. In the Diedrich 12K, for instance,
you have three settings. 80/20, 50/50, and 30/70 to
bin/drum respectively. It's almost like a gear-shift.
You pull the lever out, set it, and a spring pulls it
back in, locked into one of the above three settings.

I am not too familiar with
the Probats but on the Toper it is done by moving the drum forward or
back. The tiniest movement of this will change the flow in the drum as
it regulates the amount of air that comes in via the back of the
machine.

I've onlyu inspected Probats at the conference, but
have never even seen a Toper. Sounds... interesting.

If there is NO air flow in the roaster and you turn the gas on the temp
in the drum will just get hotter and hotter very quickly. If you have
a lot of air flow in the drum and you turn the gas on the temp will
rise, but not as quickly.

In the Quattro, if you close the blower throttle
all the way, a sensor shuts the gas off.
NO air = NO flame.
So... does the Toper completely exclude the drum
from the path of combustion products? Seems a very
inefficient way of doing things.

Remembering that when you add coffee in the drum it will also get
hotter and raise the temp even faster.

Huh? Adding 30 lbs. of 70 degree beans can only cool
the drum, not heat it...

So with no air flow your beans will burn in a
couple of minutes.

What about if you turn your flame as low as it'll
go?

With too much air flow they will bake.

It's not "too much air" that causes baking, but the
profile that tarries too long between cracks. If you
add an appropriate amount of gas to that "too much air"
you'll find your beans won't bake... matter of fact,
you've pretty much just reinvented the air roaster.

The BTU's are easier to adjust and shutting off all other gas and
tracking how long it takes for a revolution of your gas meter will tell
you what your BTU's are (I can't remember the formula but Google should
help).

Natural gas contains (very roughly) 1000+ BTUs per
cubic foot. It depends on the exact composition
of "natural gas" supplied. I only had a meter on
the roaster gas once, and it wouldn't have been
convenient at all to run out in the snow to check the
meter while the roaster was running... not to mention,
I never leave the roaster during a roast anyway.

Much more convenient and precise is a gas pressure
guage (aka manometer in some places) just downstream
of your control valve. The burner in my Quattro
runs anywhere between 1" wc and 5.5" wc. The guage
is precise to .1" wc, so basically, I have 46 distinct
and repeatable "flame levels." (Not to mention the
additional control afforded by a Watlow 935)

That is easier to control and set than a 1/100 cm difference in
the air flow adjustment.

We normally speak of airflow on this side of the
border in cfm (cubic feet per minute). If by chance
that's what you mean, then one percent of one cfm
makes no difference in the roast.

If you mean 1/100 of a centimeter, why not state
as .1 mm? At least that's unambiguous... though
come to think of it, in context, it's still pretty
ambiguous. How much is the gap that you're changing
by .1 mm? (BTW, when I made a living as a machinist,
I could routinely measure to within .1 mm with a steel
rule. Is it possible to attach one where you need to
get that precision?

Adjusting the BTU's and checking your
roasting times is probably enough learning for a new roaster.

YES !!! It does have a big impact on the taste but before you play make
sure you know what you are doing as you might never get it set back to
where you previously had it.

Maybe on a Toper. In general, I don't believe
that's the case.
.

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