HOMEBREW Digest #5516 Mon 02 March 2009

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  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 Return to table of contents
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 Return to table of contents
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