HomeRoast Digest


Topic: freeze-drying / moistening beans/cool Alp - was HotTop related (57 lines)
1) From: Bob Briggs
You are correct, Lubos, lyophilize and freeze-dry are the same thing. 
The unit I used costs around $10,000, so sales for home use is probably
a bit slow. (I'm not impressed with the new HTR end plate bearing
either.  It may, however, give new life after a drum shaft wears out
from the old end plate.  Are you going to try the new chip?)
Crudely, for those who may be interested, the lyophilizer I used has a
high-vacuum pump, thermostatically controlled shelves, and a super-cold
moisture trap.  Heat from the shelves (which must be added to accelerate
evaporation) is transferred into your product to be dried inside a
chamber which is under the high vacuum.  Evaporative heat loss under the
vacuum keeps the product frozen even if the shelves are raised well
above 0 Celcius (I've used the shelves at 30 C and the product stayed at
about -40 C.)  Large-diameter (in this case about 3") short pipes
connect the chamber to the cold-trap which re-freezes the moisture.  The
speed at which one can freeze dry is (more or less) dictated by how cold
your cold trap is, how much vacuum you can apply, and how much heat you
can add to your product.  If you place liquid water in the unit
(regardless of shelf temperature) it will boil under the vacuum until it
is frozen solid then continue to get colder even on a shelf warm that is
hot to the touch.
In my moistening experiments I don't know if the moisture was
equilibrated throughout the entire bean, but one I cut open was moist
throughout.  The moisture was entirely absorbed and the beans roasted
VERY evenly - that, and they tasted better!  Still, it's a hassle to do.
 Water vapor pressure at 18 C may be 15.5 mm of Hg, but I used 10
MICRONS of vacuum.  I figure that is on the order of 1/76,000 of an
atmosphere, 1/1,550 of the vapor pressure of water at 18C.  It's true
that very tightly adsorbed moisture may be difficult to remove, but the
lyophilizer is capable of drying commercial dessicants commonly used to
keep the contents of sealed containers dry.  I think the beans I dried
were PDD, but possibly not absolutely dry.
BTW - I first took some coffee beans into my local grain cooperative to
measure on their moisture-meter set up for soybeans.  The guy told me it
is set up for soybeans or corn - it won't work on coffee beans.  I don't
know about those electronic machines they use, but I suppose he's
right.
In regard to the cool Alp - mine slowly got cooler over time, requiring
higher and higher settings.  On alt.coffee a post commented that a
thorough cleaning solved his problem.  Cleaning mine shiny and new did
not.  I read the internal thermostat can get weak or something like
that.  Probably best to call Swissmar before warranty expires. So far
I've been too lazy to do so.  I used to dump the beans for further
cooling after the Alp dumped into the tray.  I then graduated to dumping
the hot drum as soon as the Alp goes into its cooling cycle.  A guy
doesn't want to grab that rascal with his bare hands!  I'd recommend the
purchase of a HotTop roaster for cooling your beans.  It can be set to
go directly into its cool cycle to cool hot beans from any other device
under 2/3 of a pound capacity.
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