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Topic: Valvebags and vacuum - everything has an outgas point (25 msgs / 650 lines)
1) From: Kevin DuPre
I used to work with cryogenic equipment, particularly
liquid nitrogen and liquid helium.  In order to
transfer liquid of either type you needed to insure
that no residual atmosphere remained in the cryostat
(glorified vacuum bottle) before transfer.
We used a high powered vacuum pump in order to purge
the chamber, but vacuum is a strange animal.  You see
everything has a "pressure" which either higher or
lower than atmospheric pressure.  
There is a quantum leap between 25 in Hg and 30 in
(considered a hard vacuum by most). We were able to
get to 25 relatively quickly (a matter of hours). To
get from 25 and *APPROACH* 30 (I never quite got there
for reasons below), took several more *DAYS*.
The problem is this and largely relates to the physics
of materials in a vacuum. As you increase the vacuum,
*anything* in that vacuum begins to outgas - glass,
plastic, metal, rubber, and especially anything
organic - in our case coffee beans.  There comes a
point where you simply cannot draw any more vacuum
because the rate of outgas becomes in equilibrium with
the rate you are trying to draw additional vacuum.
Where this happens is determined by the inherent
pressure of the materials in that vacuum. When drawing
a high vacuum (in excess of 29 in. Hg), you no longer
measure vacuum, but rather absolute pressure with a
specially-made blown glass gauge filled with mercury
in two columns.  The two columns provide a measure of
absolute pressure rather than vacuum, and one of the
columns is calibrated in 10th of a micron.  I remember
weeks where we would switch on the vacuum pump and let
it run for up to 3-4 days continuously to insure no
remaining atmosphere and resulting vapor pressure.
Most of the initial vacuum occurred within 3-4 hours. 
The remaining 2-3+ days were to get as much of that
last 5 inches of mercury out and hope we won the
battle against outgas pressure.
It is true that coffee beans in a vacuum will outgas
faster than if left alone in a one-way valve bag. But
it is also true that oxygen is the enemy of roasted
coffee and if you use the vacuum to purge nearly all
the oxygen (which is quite possible if your equipment
draws 25" Hg), the one-way valve in the bag prevents
the ingress of outside air containing oxygen back into
the bag while allowing buildup of excess CO2 to
escape.  All that remains is the outgassing of the
beans into the remaining space in the bag - the
purpose of the one-way valve is to let out the excess.
 No valve and your bag would look like a balloon
withing a couple of days - I've seen a bag with
roasted coffee and no valve - it's really interesting
that THAT MUCH CO2 builds up, but it does.
But as the CO2 is escaping the beans and refilling the
space left by the vacuum that is OK - it's protecting
the flavor of your roast.
The problem occurs when the bag is opened for use and
air gets back in.  
Re-vac'ing and resealing the bag will prolong the
life, but there comes a point of diminishing returns -
oxygen wants into the organic structure of the roasted
beans - it occurs at a molecular level - a little gets
in with each opening, no matter how much you vac back
out. When it reaches equilibrium within the structure
of the bean, the game is over and stale coffee is the
result.
According to Kenneth Davids who as most of you
probably know [I don't mean to insult anybody's
intelligence and experience in saying this] wrote a
very good book on home roasting, "[following roasting]
The carbon dioxide gas gradually works its way out of
the bean in a process called degassing, which
temporarily protects the flavor oils from the
penetration of oxygen and staling (Of course when the
CO2 is finally gone, so is flavor. Vacuum cans,
nitrogen-flushed bags, and so on are all artificial
efforts to protect the coffee from the staling
penetration of oxygen... And when the natural
protective package formed by the bean is destroyed by
grinding, the protective gas disappears even more
quickly)."
Based on this and my experiences using high vacuums in
an industrial environment and logging outgassing
related to everthing from plastics to rubber to
silicone grease used to insure a good seal of those
rubber O-rings to aluminum to cured epoxy to stainless
steel, repeated high evacuation of a container like a
canning jar or apothecary jar (with lots of empty
space above the beans) will accelerate the degassing
due to the space and residual vacuum in that space,
unlike a bag which collapses on the beans within and
practically limits the amount of residual vacuum which
remains surrounding the beans.
I would think, IMHO, that the only concern and reason
for pulling vacuum on a jar after the first pull was
because the jar was opened and air allowed to get back
in. Beyond that, simply pulling a vacuum to force
additional degassing is to shorten the life expectancy
of the roast.
=====
--
Kevin DuPre
obxwindsurfhttp://www.virtualfusion.com"The real voyage of discovery consists not in seeking new landscapes but in having new eyes -- Marcel Proust"
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2) From: Rick Farris
Kevin wrote:
<Snip>
That part makes my head hurt. :-)  The "amount" of vacuum, where you *don't*
mean the vacuum pressure?  Oy.
<Snip>
I would add "Because by opening the jar with a partial vacuum inside, you
reintroduce oxygen to the container, some of which will not be removed by
the re-vacuuming."  I don't think vacuum, per se, or additional degassing is
harmful.
-- Rick
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3) From: TFisher511
rick writes:
<Snip>
I think that the point is that when the jar is opened just to re-vac, the new 
oxygen allowed to enter the jar probably will do more harm than just leaving 
the beans in their original CO2 environment. On the other hand, if you take 
time to really enjoy the aroma of the coffee when the seal is broken to 
re-vac the beans, then I would imagine the pleasure derived from the aroma is 
more than worth the minor additional detriment to the beans from the 
additional exposure to oxygen.
It sounds like the moral to this whole discussion may be heading toward a 
saying we have heard for years, even before home roasting. It must be time to 
wake up and smell the coffee.
Terry F

4) From: Dan Bollinger
<Snip>
*don't*
<Snip>
Maybe this will help with the headache!  I read here vacuum bagging is good
for 25" Hg.  That's about 5/6 vacuum (30"Hg is max).  That means that 5/6th
of the gas has been removed and 1/6th remains whether is was CO2 or O2.
Pacific Bag sells the little degassing valves.http://www.pacificbag.net/degassing-valve.htmlDan
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5) From: Rick Farris
I wrote:
<Snip>
Don replied:
<Snip>
That's the vacuum pressure, Don.  See that word "don't" up there, with the
emphasis around it?  The situation you describe doesn't hurt my head in the
least.  ;-)
The OP was talking about the situation where you have, for instance, two
containers, both at 25" Hg, but one is a pint container and one is a quart
container.  The quart container has "more" vacuum!
In electrical terms, the containers are like capacitors, where the quart
container has more capacitance than the pint container.  If they are both at
the same voltage (vacuum pressure), it will take more electrons (outgas
molecules) to raise the voltage (pressure) a given amount.
Therefore, if I have two containers of differing sizes with the same amount
of beans roasted to the same level in them, the larger container will
maintain a higher (lower?) vacuum pressure for longer.
Ok, now my head doesn't hurt anymore.
-- Rick
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6) From: Rick Farris
(Jeezus, now I'm replying to myself.  Have I lost it, or what?)
Don wrote:
<Snip>
To which I replied:
<Snip>
But on the third hand: In the case of a pint container and a quart
container,  even though the vacuum pressure would not change as much in the
larger container, there would be twice as many oxygen molecules left inside
(at the same pressure) and if there were the same number of beans, there
would be twice the oxidizing power in the larger container.  Oy.
-- Rick
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7) From: EskWIRED
<Snip>
Yep.  It seems to me that hard shell containers will inevitably leave many
more O2 molecules compared to bags.  And given equal canisters, the one with
the least amount of headspace will have the least number of O2 molecules.
Does anybody have an opinion about whether the Tilia bags work better than
the canisters?
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8) From: R.N.Kyle
This is a multi-part message in MIME format.
You know there is nothing sweeter then the smell, when you crack several =
sealed jars of fresh roasted coffee. a little bit of heaven IMHO
Ron Kyle
a coffee roaster from South Carolina
rnkyle

9) From: Angelo
There seems to be a simple solution for the headroom "problem". Just fill 
the remainder if the jar with some other material that will not interact 
with the beans, nor be pulled out by the vacuum.....I'm sure the engineers 
on the list could suggest the best material. In my ignorance, I would offer 
sand.....
A-
<Snip>
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10) From: EskWIRED
<Snip>
That would certainly fill all the spaces between the beans, but something
more easily removable might work better.  Do packing peanuts expand like
marshmallows do in a canister?  If so, they might work well.  Or are they
full of air bubbles?
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11) From: Maria Tsang
Anybody heard of an Arabica specie called the 'Catimo'? Not sure about the
spelling.
It's a very good for blending espresso roast coffee.

12) From: Charlie Herlihy
<Snip>
"problem". Just 
<Snip>
 No offense, but you guys are going over the edge
trying to find a way to get rid of the very last o2
molecule. Sand in your expensive grinders or packing
peanut bits in your brew are not worth risking for an
extra 5 minutes of absolute freshness in your
vacpacked coffee. Or are they....;o)
Charlie
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13) From: Jeffrey A. Bertoia
I agree Charlie...
However no one has suggested another Gas.
Illy uses nitrogen.  In fact it is my understanding that instead of 
vacing their
coffee it is actually under pressure after being flooded with nitrogen.
jeff
Charlie Herlihy wrote:
<Snip>
-- 
Jeffrey A. Bertoia                      jbertoia
Slalom Services, Inc.                   www.SlalomServices.com
Telephone: +1 (810) 220 - 1174          Mobile: +1 (586) 854 - 7312
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14) From: Eric B. Stauffer
What about something like this:http://www.wineenthusiast.com/shopping/prod_detail/main.asp?cat&catID&sl=0&productIDB4
Eric

15) From: Dan Bollinger
<Snip>
Jeff
I mentioned nitrogen awhile back, too, but no one responded.  I think it is
more practical solution than vacuum.  For one thing, you don't have to worry
about a vacuum leak.  Nitrogen is used extensively by companies making
survival food and they garaurantee freshness for 10+ years.  It has a
naturally low reactivity. I use it for preservation, too, but not for
roasted coffee.  I'd rather amass a store green beans and roast as I need
them instead of amassing roasted beans and invest in all the paraphenalia
that goes along with them. Dan
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16) From: Rick Farris
Charlie wrote:
<Snip>
Are we, or are we not, CSAs?
Besides, if you want to talk about being over the edge, which one of us is
it that goes down to Mexico and walks around in the interior just so he can
hump a 55 kilo sack of coffee down some dirt trail because Tom's coffee just
isn't quite good enough, eh?  :-) Now *that's* over the edge.
-- Rick
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17) From: Rick Farris
Dan wrote:
<Snip>
Yeah, but every now and then, Dan, there comes a time when for one reason or
another I might not be able to roast for a couple of weeks.  What am I
supposed to do that second week?  Drink stale coffee?
-- Rick
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18) From: Charlie Herlihy
Rick Farris wrote>Are we, or are we not, CSAs?
Besides, if you want to talk about being over the
edge, which one of us 
is
it that goes down to Mexico and walks around in the
interior just so he 
can
hump a 55 kilo sack of coffee down some dirt trail
because Tom's coffee 
just
isn't quite good enough, eh?  :-) Now *that's* over
the edge.
-- Rick<
Obviously the one who puts sand in their "almost good
enough" beans for some esoteric quest of the perfect
vacume is more over the edge. Going a little bit out
of the way for the best beans only makes good CSA
sense. ;O)
 Charlie
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19) From: Steven Dover

20) From: Dan Bollinger
<Snip>
can
<Snip>
just
<Snip>
When do we leave?  :)
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21) From: Dan Bollinger
<Snip>
or
<Snip>
Hell no, don't drink stale coffee!  Sure, preservation is one solution, but
then so is going to a coffee shop!  ;) Dan
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22) From: Angelo
Hey! I only SUGGESTED using sand as a filler. I didn't say I would do it...:-)
(Does that mean I've lost my membership in CSA? Gosh, I hope not)
A-
At 01:21 AM 8/14/2002, you wrote:
<Snip>
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23) From: Charlie Herlihy
Dan Bollinger posted> Besides, if you want to talk
<Snip>
 > it that goes down to Mexico and walks around in the
<Snip>
because Tom's 
coffee
just
<Snip>
the edge.
<Snip>
When do we leave?  :)
  November. The best of the best highest grown isn't
ready to be picked untill feb., but if the growers
don't know in advance that someone is willing to pay
something aproaching the cost of production then they
probably won't bother doing the preharvest weeding and
other preparations.Most of the best plots have been
abandoned in the last 3 years. If they know that
someone's willing to pay something approaching a fair
price (1.20lb. or so, FOB(freight on burro) then
they'll actually pick only the ripest cherries, hand
wash with gentle care and sun dry and hand grade with
the greatest skill and pride. Fluency in the Zapotec
language isn't mandatory, but some polite greetings
and other "icebreaker" phrases do help a lot to
despell suspicions that you might be just looking for
drugs or even children to steal for their body parts
(not a lot of gringos wandering around up there so you
must be up to something, right?) Of course your
Spanish had better be very good and it goes without
saying that you're in shape to walk straight up and
down for hours on end, fording streams and so forth.
There's even St.Helena quality stuff hiding here and
there, some years. Make a bad on the spot cupping
decision, though, and the bag you carry down could be
a big disapointment when you get it home. Burro
rentals, when available, are a good investment BTW.
Hope this helps. ;o)
Charlie
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24) From: TFisher511
sd218 writes:
<Snip>
I can tell you *undoubtedly* this seasoned coffee drinker will not tolerate 
stale coffee flavors that I once considered to be the norm. It sounds like 
you are probably too young to be making that kind of statement.
That's just my 55 sense worth :)
Terry F

25) From: Ben Silva


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