HomeRoast Digest


Topic: Vacpot preheating (10 msgs / 230 lines)
1) From: Jeff Kilpatrick
Hello-
The recent talk of learning a Yama has me evaluating my own techniques.  A
while back, I started pre-heating the bottom to 180 degrees before adding
the top.  I find that this and using the lid increase the chances that the
infusion will be at a proper temperature.  As a result, it's been about 195
during the outgassing (the "boil" during which water vapor escapes the
bottom and creates bubbles in the top).
My question is, had I been doing something wrong?  Am I still?  Is anybody
else getting really low temperatures just following the instructions?
Thanks,
-jeff
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2) From: Douglas Hoople
Hi Jeff,
Pre-heating the bottom strikes me as totally redundant, since heat gets
applied after the water is added, and the water won't rise until it's at the
right heat. It's possible that pre-heating the top will make a difference,
but not the bottom.
BTW, 195 is low, but it's within the 195-205 degree range for making coffee
properly.
I haven't measured temperatures, but I've been getting great coffee from my
vacpot. Are you unsatisfied with the quality of your coffee, or are you
unhappy that you're getting coffee that's not hot enough for your taste?
Doug
On Wed, Jan 21, 2009 at 10:21 AM, Jeff Kilpatrick 

3) From: Jeff Kilpatrick
Doug-
I also always assumed that pre-heating was redundant.  I've also been pretty
pleased with the coffee that comes out of my Yama.  It's always been fairly
different from what I get out of a press, but that's a different story all
together.  I got onto this because I had a new thermometer and poked it in
out of boredom and found that the temperature was really low -- about 160 in
the top.  In fact, as I kept messing with it, I'm finding that the
temperature only goes up 25-30 degrees from the time the top is added until
outgassing starts -- this assumes preheating, so if you start from a cold
burner on an electric stove, YMMV.
Thinking back to physics classes, this kinda makes sense.  Assuming the
water isn't boiling, it's not going to expand too much.  That means it's
getting pushed into the top by the increase in temperature of the air in the
bottom.  By the ideal gas law, PV = nRT, where V, n, and R are constant in
this case.  In other words, no matter where the temperature (T) starts
(within reason), the increase in pressure (P) will pretty much be the same.
 So starting with cold water means it's going to infuse cold.  Of course,
I'm not that kind of scientist, so I invite corrections.
As far as the taste goes, I've been roasting a while, but only recently have
I /really/ been paying attention.  Different flavors certainly come out at
higher temperatures.  It seems like the only tastes that survive using my
old method are blasts of bass or intense fruitiness.
Is anybody interested/willing to measure their starting and ending vacpot
temperatures?  I'm starting to think that I've gone insane.
Thanks,
-jeff
On Thu, Jan 22, 2009 at 11:38 AM, Douglas Hoople wrote:
<Snip>
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4) From: Douglas Hoople
Hi Jeff,
Two things in what you say make perfect sense.
1) that whatever the temp, any increase will drive the water north, and
2) you're starting with cold water.
So that means you would have been driving cold water north into the upper
chamber.
To me, that makes it all the more important to start with water that's
pre-heated in the kettle. That would seem to neutralize most of the negative
effects of what you're observing.
I brewed a pot just now to see what I'd get using pre-heated water.
195-197 in the upper chamber throughout the heating cycle, and 198 (!) in
the lower chamber after the brewing was over.
The temps are on the low end of acceptable, but they are definitely
acceptable, and I've had some great coffee in the week that I've had this
pot.
Tom strongly recommends pre-heating the water, but he does mention starting
from cold, saying only that it takes a long time.
Based on your observation, Jeff, I'd upgrade the recommendation to a mandate
to pre-heat the water. Starting from cold means brewing well below the
optimal range for good coffee.
Thanks for the information and the insight!
Doug
On Fri, Jan 23, 2009 at 10:35 AM, Jeff Kilpatrick 

5) From: Ben Lowery
<Snip>
Jeff, I'll check it next time I run a brew. FWIW, I preheat the water
to a boil and then let it sit for short time before adding it to the
vacpot. Once I attach the top globe, water starts moving northward
almost immediately. All of the water is in the top globe after about a
1:00 ~ 1:30.
--b
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6) From: Rich Adams
The instructions included with my Yama say to start with hot water.

7) From: Bill
Remember, the vacpot and the mokapot both function using pressure, not
temperature.  and we're fast approaching the end of my rememberance of high
school chem!  but yes, you need the water in the bottom globe of a vacpot to
be near boiling before putting the top on it to get good temps.  the nice
thing about the vacpot is that at sea level, the water in the upper globe
shouldn't surpass 200F.  At 6000 ft, where I live, that means that the
vacpot doesn't top much about 190F, not that I could ever taste the
difference in flavors!
so even if you are starting with cold water, you just heat it before putting
the top globe on.  and frankly, i always found it took about 45 seconds to
take my boiling water from the kettle to boiling with the VP...
ymmv
bill
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8) From: Jim Wilson
Jeff said:
<Snip>
~~~This is a good thread.  I've never tasted what I would call a bad cup iof vac pot since I started using one, last December, so, I have been in this fraternity for only a couple months, yet I've had nothing but good results
here's what I do-
I'm heating on an electric stove, modern type, no coils, it's a flat surface.  I place the wire on the surface, typically I'll run my hot water kitchen sink faucet til it's hot and I know the temp, it's approx 138 degrees when I let it run (yes I have measured my hot water temp at the faucet, more than once)
the 5 cup pot gets filled just above the 5 cup mark with this hot water.  if I'm in a hurry, I turn the element on high, watch for it to start moving, then I turn it down to meduium, then to low
I have never measured the temp of the water going into top but I have an idea it's right around 200 degrees F.  maybe it's time I measured this temp...like I said, this is a good thread
= : - )
Best,
Jake
Reddick Fla.
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9) From: Angelo
<Snip>
I'm not so sure it's a good idea to drink hot water from the tap. 
Most plumbers I talk to don't recommend it...
Angelo
<Snip>
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10) From: Bob Luis
The other I measured the temp in the bottom at about 195F when I put the
top of the Yama on.
I measured the temp in the top during its one minute brew to be over 200=
F.
FWIW
Bob
On Tue, Jan 27, 2009 at 11:25 PM, Jim Wilson  wrote:
<Snip>
ot
<Snip>
ee.com
<Snip>
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