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Contents:
Re: Slaking heat (Fred L Johnson)
re: Slake Heat (Matt)
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Date: Mon, 2 Mar 2009 07:49:35 -0500
From: Fred L Johnson <FLJohnson52 at nc.rr.com>
Subject: Re: Slaking heat
This discussion slaking heat appeals to my analytical bent, so I
apologize for those who find this stuff a waste of time, which it
probably is.
I must say that I don't understand why the full amount of slaking
heat is not considered in the formula, i.e., why the formula includes
only "0.5 h". Do I understand correctly that this is simply
someone's attempt to enter a fudge factor into the formula for heat
losses, or is A. J. saying that there is a thermodynamic principal
being captured by this factor?
It seems that all of the heat would be distributed among the grain,
the water, and the tun, (or to the surroundings if it all of these
are perfectly insulated, which , of course, they are not) and that
all of the mass and specific heat of all of these must be considered
in calculating the temperature rise of the mash. Others have pointed
out that the entire mash tun is not heated uniformly during the mash-
in process and that there should be adjustment for the portion of the
tun that gets heated and to what degree--a very complicated
calculation. Nevertheless, if heat is generated during the mash, then
we should somehow be taking this into account in our calculations of
strike water temperature.
Fred L Johnson
Apex, North Carolina, USA
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Date: Mon, 2 Mar 2009 07:56:54 -0800 (PST)
From: Matt <baumssl27 at yahoo.com>
Subject: re: Slake Heat
AJ says "For small (5 gallon batch) mashes the ratio is
quite high and the slaking heat is likely to be lost
through the larger surface before its effects are noticed."
Well, heat is heat. But anyway I think (?) you're really
suggesting that since slaking heat will generally be less
that what's lost to the thermal load of a low-volume mash
setup, we can assume on the whole the temperature will
still "drop" compared to an ideal calculation with just
water and grain.
Slaking heat will cause it to drop less than it otherwise
would--but one might suspect we could deal with that by
including an "effective thermal mass" in the calculation,
which accounts not for the actual thermal mass but for the
practical difference between the effects of thermal mass
and slaking heat.
As I mentioned earlier, this is just what I do for single
infusions near my usual temperature, mash thickness, with
my grind, etc. At this operating point, slaking heat seems
to cancel surrounding heat loss to within 1F so my "effective
thermal mass" happens to be zero.
Where the problem arises, in my experience, is if you try to
use that same "effective thermal mass" for step infusions at
a different operating point (lower temp, thicker mash, etc).
For the first infusion in the schedule, you get about the same
total slaking heat, but with less water the associated temp
increase is much *higher*, plus heat loss to surroundings is
*smaller*. If I try to calculate an infusion to 113F, using
my normal "effective thermal mass," I end up at 119F!
Then I add water to make my step infusion, and of course there
will be no slaking heat at all this time. It therefore
requires *much* more boiling water to hit my next rest temp,
than I would predict using my normal "effective thermal mass."
So for me, slaking heat effects and thermal load effects CAN
be lumped into one fudge factor (which happens to be near zero)
for single infusion mashes near 150F and 1.5 qt/bl.
BUT this approximation does NOT work (in theory or in practice
on my system) over the wider range of temps and thicknesses
associated with step mashing. YMMV.
I do agree that coming up with something that DOES work well
(say within 2F) is a rather formidable challenge for the reasons
AJ mentions. Coming up with something that just works *better*
than the single fudge factor approach is less formidable--but
also may not be worth the effort for a lot of folks versus trial
and error and quick additions of hot/cold water.
Matt
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End of HOMEBREW Digest #5516, 03/02/09
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