Author Topic: Accounting for Water Under a False Bottom  (Read 3474 times)

Offline dcbc

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Accounting for Water Under a False Bottom
« on: February 22, 2012, 12:28:17 PM »
I just revamped my system and went from a 70 qt Coleman Xtreme with a Bazooka screen to a 20 Gallon Kettle with a false bottom.  In ironing out the bugs of which I became aware on my inaugural brew, figured out that the false bottom sits about 2.25" above the bottom of the kettle, which amounts to roughly 2  gallons of strike water that isn't in contact with any of the grist until I begin to recirculate (usually about half way through the mash or later). 

For a 10 gallon batch with a grain bill in the low to mid  20 lb range, I mash in with 9 gallons of water and batch sparge.  When I did this on my first batch on the new system, my mash temp came in low and the water to grist ratio was way thick.  I added about 1.5 gallons of boiling water to get my mash temp up and extended my rest by 30 minutes.  In the end, all was well, but it is obvious that I need to account for this.

So my plan is to simply add 2 gallons of water to my strike water, adjust my mineral and/or acid additions to the mash based on the total gallons of strike water, i.e. 11 gallons, but treat my water to grist ratio and strike water temperature calculation as if I were only using 9 gallons of water since the grain isn't going to come into contact with any of that water beneath the false bottom until I recirculate, and, presumably, at that point, most, if not all of my conversion is complete.  I would reduce my sparge water volume by the 2 gallons I added to the strike water.  Does this sound like I'm on the right track?

Alternatively, I could always rig up a bazooka screen to my kettle dip tube and eliminate all of this adjustment.  If I went this route, has anyone run into issues recirculating/transferring with a pump using a bazooka screen in a mash tun?
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Offline tschmidlin

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Re: Accounting for Water Under a False Bottom
« Reply #1 on: February 22, 2012, 12:36:42 PM »
On the right track, but you need to include the full volume in your temp calculations.  The water may not have any grain in it, but as starch and sugar dissolves into the mash some of it will end up under the false bottom. Your first drops of wort when you recirculate will definitely not be watery looking, to me it looks just as dark as the rest of the mash (although I haven't pulled samples and looked side by side).  Conversion will happen there too.

Ignore the 2 gallons for the water/grist ratio or else you may end up with dry grain, but include it for everything else.
Tom Schmidlin

Offline dcbc

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Re: Accounting for Water Under a False Bottom
« Reply #2 on: February 22, 2012, 12:41:41 PM »
Thanks, Tom.  Just for clarification, are you saying that the total thermal mass of the 11 gallons of water will have an effect on the the mash temperature.  Or are you saying that because the wort will end up in the water below the false bottom, it is better to include that water in the strike water temperature calculation so I don't have water below the false bottom that has not reduced in temperature since it has not been mixed with grain and, therefore, has the potential to denature enzymes? 
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Offline tschmidlin

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Re: Accounting for Water Under a False Bottom
« Reply #3 on: February 22, 2012, 12:44:57 PM »
The thermal mass will have an effect on the mash temp, at least in my experience.  If you missed low before I would look to something else as the cause, because the physics of temp stabilization after mixing water/grist is pretty straightforward.  If it is taking too long to stabilize or you have stratification, you can do a quick recirc when you dough in to even things out.
Tom Schmidlin

Offline dcbc

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Re: Accounting for Water Under a False Bottom
« Reply #4 on: February 22, 2012, 12:58:32 PM »
Yeah, there were several issues in my missing low (by 11 degrees) on that inaugural brew.  Didn't preheat the tun (with the cooler, I could just go 10 degrees higher and seal it up for several minutes, then let it drop down to strike temp).  Hoses were too long and I was getting air in the lines.  I think one of my QDs had a seal loose as well.  I was already going to change these out for the camlock qds.  So that should not be an issue next time.  I also broke down and ordered the high flow impeller for the march pump.  But, long story short, my transfer took a while and I probably lost plenty of heat.

But two gallons is quite a bit of water not initially in contact with the grain and I can't help but wonder that it maybe should not be given full consideration in strike water temperature calculation.  I have nothing to back that up though.  And, of course, I would rather come in too low rather than too high.  So, if I use 11 gallons to determine my strike temp, preheat the tun, and have a normal transfer from the HLT and still come in way low , I'll, at least, be that much closer to getting things dialed in.   

Thanks again for your help.
« Last Edit: February 22, 2012, 01:07:05 PM by dcbc »
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Offline bluesman

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Re: Accounting for Water Under a False Bottom
« Reply #5 on: February 22, 2012, 07:38:33 PM »
The thermal mass will have an effect on the mash temp, at least in my experience. 

+1

You need to account for this mass of water before, during and after the mash. It must be accounted for in temp calculations as well as volume (water:grist) ratios. It also holds sugar and will be responsible for some lautering efficiency losses.
Ron Price

Offline tschmidlin

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Re: Accounting for Water Under a False Bottom
« Reply #6 on: February 22, 2012, 07:54:08 PM »
The thermal mass will have an effect on the mash temp, at least in my experience. 

+1

You need to account for this mass of water before, during and after the mash. It must be accounted for in temp calculations as well as volume (water:grist) ratios. It also holds sugar and will be responsible for some lautering efficiency losses.
I ignore it for water/grist ratio, because if I'm making 5 gallons of something low alcohol it can leave the grain at the top of the bed too dry, and I've only got ~5.4 liters under the false bottom.  Since he's got more like 7.5 liters it will be more of an issue for him.
Tom Schmidlin

Offline bluesman

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Re: Accounting for Water Under a False Bottom
« Reply #7 on: February 22, 2012, 07:58:28 PM »
The thermal mass will have an effect on the mash temp, at least in my experience. 

+1

You need to account for this mass of water before, during and after the mash. It must be accounted for in temp calculations as well as volume (water:grist) ratios. It also holds sugar and will be responsible for some lautering efficiency losses.
I ignore it for water/grist ratio, because if I'm making 5 gallons of something low alcohol it can leave the grain at the top of the bed too dry, and I've only got ~5.4 liters under the false bottom.  Since he's got more like 7.5 liters it will be more of an issue for him.

I have about three quarts of dead space below the false bottom which can be a factor on some of my beers. I use Beersmith and have the program setup for my system so it's always factored into my process.
Ron Price

Offline dcbc

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Re: Accounting for Water Under a False Bottom
« Reply #8 on: February 22, 2012, 08:39:52 PM »
I see an adjustment for dead space in my equipment profile in Beersmith, but where is the adjustment for water under the false bottom that is otherwise lauterable?  Dead space would still be calculated into the liquor:grist ratio.
« Last Edit: February 23, 2012, 08:55:32 AM by dcbc »
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Offline ccfoo242

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Re: Accounting for Water Under a False Bottom
« Reply #9 on: February 25, 2012, 10:15:29 PM »
I see an adjustment for dead space in my equipment profile in Beersmith, but where is the adjustment for water under the false bottom that is otherwise lauterable?  Dead space would still be calculated into the liquor:grist ratio.

Not sure if I did it correctly but I drained mine until the flow stopped then I measure how much was left in there, then I entered that into the mash tun dead space value.

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Offline tygo

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Re: Accounting for Water Under a False Bottom
« Reply #10 on: February 25, 2012, 10:24:54 PM »
What you lose in the mash is a combination of the losses to deadspace and the water absorbed by the grain.  If your grists are relatively consistent in terms of lbs of grain then it doesn't matter.  You know how much you're going to lose. 

My differences arise when I'm mashing a much larger quantity of grain than my standard brews.  Since I take careful measurements with each brew, and I have a ton of data points I think a formula could be written to quantify the amount of deadspace vs grain absorption.  I actually wouldn't bother if my wife weren't a math teacher who lives for these kinds of word problems  ;D

I just need to give her my data and she can punch it up in her graphing calculator.  Just haven't gotten around to it yet.
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Offline ccfoo242

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Re: Accounting for Water Under a False Bottom
« Reply #11 on: February 25, 2012, 10:34:39 PM »
What you lose in the mash is a combination of the losses to deadspace and the water absorbed by the grain.  If your grists are relatively consistent in terms of lbs of grain then it doesn't matter.  You know how much you're going to lose. 

My differences arise when I'm mashing a much larger quantity of grain than my standard brews.  Since I take careful measurements with each brew, and I have a ton of data points I think a formula could be written to quantify the amount of deadspace vs grain absorption.  I actually wouldn't bother if my wife weren't a math teacher who lives for these kinds of word problems  ;D

I just need to give her my data and she can punch it up in her graphing calculator.  Just haven't gotten around to it yet.

Have you messed with beersmith? It includes grain absorption and dead space when calculating the water you need for a mash. I think it needs to be tweaked for different people's equipment but from the little but I've used it, it seems to do a decent job.

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Offline tygo

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Re: Accounting for Water Under a False Bottom
« Reply #12 on: February 25, 2012, 11:19:09 PM »
Yep, beersmith is the brewing software I use.  But you still need to know what values to input for grain absorption and dead space.  The information the software gives you is only as good as the information you give it.
« Last Edit: February 25, 2012, 11:21:21 PM by tygo »
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Offline dcbc

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Re: Accounting for Water Under a False Bottom
« Reply #13 on: February 26, 2012, 06:23:34 PM »
I understand what dead space is.  However, I don't consider water under the false bottom that is otherwise lauterable to be dead space.  If after draining, I have 0.5 gallons of water left, that is my dead space.  However, I have more room than 0.5 gallons under my false bottom.  I suppose it only really matters in a liquor:grist adjustment, but it would help to have that variable available. 
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