HOMEBREW Digest #5517 Tue 03 March 2009

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  Re: Slaking heat (bill keiser)
  simple(ish) way to account for slake heat (Matt)

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---------------------------------------------------------------------- Date: Tue, 03 Mar 2009 07:26:27 -0500 From: bill keiser <bk2 at sharpstick.org> Subject: Re: Slaking heat i've never seen this done, but can you pour out a couple quarts every few minutes, reheat with a double boiler or microwave to strike temp and pour back in to keep the temp flat during mash? this would be doable for those of us primitive brewers who are using an old hacked up cooler instead of a fancy brew sculpture. bill keiser > . . . 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 > Return to table of contents
Date: Tue, 3 Mar 2009 08:59:50 -0800 (PST) From: Matt <baumssl27 at yahoo.com> Subject: simple(ish) way to account for slake heat I think the following may be the simplest way to include slake heat in mash temp equations. (BTW I haven't been academically precise with physical definitions and units. Note also that slaking heat of course only applies to the first infusion, in which dry malt is hydrated.) Any decent existing mash temp equation already has a term (we'll call it "A") that accounts for initial heat that the dry grain brings to the table. This'll look something like A = grain_mass * grain_heat_capacity * temp_of_grain. (In Bill's version this is the term Tg*0.4*Wg.) However, the grain also brings extra "slaking heat" to the table as it gets hydrated. The total heat the grain brings is then B = ( grain_mass * grain_heat_capacity * temp_of_grain ) + ( grain_mass * grain_heat_of_hydration ) To account for slaking heat we might just replace A with B in our equations, but it may be more simple/practical if we re-arrange B: B2 = grain_mass * grain_heat_capacity * ( temp_of_grain + bonus_slake_temp) where we've invented a "bonus_slake_temp" with units of temperature. This technically equals grain_heat_of_hydration divided by grain_heat_capacity -- the amount by which the slaking heat would increase the temp of the dry grain itself. An approach to finding the value of bonus_slake_temp on a given system is below. THE POINT IS THAT THE EFFECT OF SLAKE HEAT CAN BE ACCOUNTED FOR BY JUST ADDING A LITTLE "BONUS" TO THE INITIAL DRY GRAIN TEMP. One could do this even with existing computer implementations (spreadsheets, promash) that don't explicitly address slaking heat. Thus we have two "fudge factors": mash tun thermal load and "bonus slake temp". These can BOTH be calculated for a given system, based on a single mash that includes two infusions (such as a single infusion to 150F, plus a mashout infusion) as long as we carefully record the volume and temp of water, and initial and final mash temp, for each infusion. To calculate the fudge factors we'd start with the second infusion: slaking heat is not a factor there so the "mash tun thermal load" can be found on its own. Then, with knowledge of the mash tun thermal load, we'd tackle the first infusion and find the value of bonus_slake_temp that makes the calculation match reality. I won't go into the math--if you've bothered to read this far you're surely geeky enough to do it on your own. Simple methods with a single fudge factor are certainly good enough to work well in a narrow operating range (say, for single infusions near 150F). That's what I do and I'm happy with it. But they don't work as well for step mashes with protein rests and I'd wager this two-fudge-factor method would work a lot better. I haven't tried it but I will. Matt Return to table of contents
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