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Old 08-12-2010, 03:07 PM   #1
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Default Batch Sparge Gravities

I've been looking over Kaiser posts but can't figure out the answer to this.

It there a way to figure out the gravity of each running in a batch sparge?
The decline in gravity must follow some sort of curve.

Say my first runnings and two batch sparges are all equal volume and I knew that my total pre-boil wort gravity was 1.042. Using a half-life assumption I'd get:

First Runnings = 1.072
First Batch Sparge = 1.036
Second Batch Sparge = 1.018

That's guessing that each running has half the gravity as the one before, but that is just a guess. Anyone know what that number actually is?


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Old 08-12-2010, 03:19 PM   #2
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it greatly depends on your system - the amount of dead space in your tun, for example. In my system, for an 'average' gravity recipe, I get approximately 85-90% of my sugars in the first runnings, at a mash thickness of about ~2.5qt/lb - i.e. when I 'no-sparge' by adding in the sparge water before beginning the runoff, my overall efficiency goes down by 10 or 15%


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Old 08-12-2010, 03:55 PM   #3
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What I'm looking for is a constant in the decline of gravity over a series of lauters that would be proportional to your efficiency (and system), but not dependent on it. I would think it would be contingent on the grains ability to hold sugar from one lauter to the next.



Edit:
It's probably effected by the type of grain and the crush, but I was hoping that some generalizations could be made.
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Old 08-12-2010, 04:03 PM   #4
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that, in turn, would be dependent on your system, though, would it not? How fine you crushed, how long you let it rest between run-offs, possibly the temperature, whether or not you used a mash-out, whether or not you stir your mash, the geometry of your mash tun (the weight of the column of grains could wring out more sugars).

Such a constant would therefore only be applicable to the system it was measured on, assuming that consistent processes were followed brew after nrew
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Old 08-12-2010, 04:09 PM   #5
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There are some generalizations made for each sparge round, at least in information I've come across for partyguilling purposes. I remember coming across it when I did that pumpkin partigyle a couple years back.

IIRC the numbers are mentioned in some of the links in my old thread http://www.homebrewtalk.com/f36/lets...ne-mash-74927/ I tihk it's in Randy Mosher's article;

http://www.brewingtechniques.com/lib....2/mosher.html

There's some tables there it may give you a rough guestimet, or at least help you figure out how to get that guestimate.
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Old 08-12-2010, 04:19 PM   #6
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This table may help. It give the breakdown of each round based on the OG of the total, but it does it for a 1/3 + 2/3 split or a 50/50 split in partyguile batches.

http://www.brewingtechniques.com/lib...shertable.html
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Old 08-12-2010, 05:07 PM   #7
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Great stuff Revvy! It looks like the half-life estimate holds close to true. It's right there on the 1/2 -1/2 split chart and close on the numbers that Mosher comes up with when doing three equal runnings. Thanks.

My simplified math for three runnings went like this:

AG = Average gravity of entire batch
BC = Batch constant

BC = 3 * AG / 7

Gravity of 1st sparge = 4 * BC
Gravity of 2nd sparge = 2 * BC
Gravity of 3rd sparge = BC
(w/ three equal sparge volumes)


Quote:
Quote Mosher:
Thus, a 16 P entire batch will yield 5 gal of beer at 24 P, 5 gal at 16 P, and 5 gal at 8 P. Actual gravities will vary from batch to batch, depending on many factors; these estimates provide a starting point only.
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Old 08-12-2010, 05:11 PM   #8
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I charted a few of my brews, and they dropped ~50% from mash runnings, 1st sparge, 2nd sparge...

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Old 08-14-2010, 03:29 PM   #9
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That's been my experience too. ~ 50% each step.
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Old 08-14-2010, 04:15 PM   #10
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The last batch I checked was 46%, 30% and 24%


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