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Mash Volume Calculations

CraigF

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Okay - i'm finally asking the question(s) that i should have when first starting to BIAB.

I have a straightforward excel spread sheet which computes required mash volume taking inputs (desired fermenter volume, lbs of grain, shrinkage, quantity of hops, boil losses). For this recipe: 30.6 lbs grain, 11G into fermenter, 3.1 grain absorption, 1.5G boil loss, shrinkage computes to 16.2 Gallons required.
In BS - I enter comparable quantities and BS computes 18.3Gal.

I'd like to use BS to guide me on water adjustments, so getting mash volume is important - what am i missing?
thanks
 
First thing to note is that BeerSmith calculated the water volumes for anything pre-fermenter as hot water. If your spreadsheet calculates based upon room temperature water, then you will need to account for the thermal expansion when comparing any numbers.

If you take a look at your recipe and go to the 'vols' tab, you can see the amount of water for each stage of the process. Compare these numbers to the ones you use in your spreadsheet. This will give you an idea of where you may need to look for adjustments in the BeerSmith parameters. Many of these parameters can be found in the 'options' > 'advanced' section of BeerSmith.
 
Determining actual volumes needed for mash is empirical. In other words, it requires some trial-and-error. You need to find out how much each variable affects your brewing process. BeerSmith is set to defaults that are rough estimates, but you will need to adjust those for your own equipment/processes. Thermal expansion accounts for about 4% change cold to hot, but that 4% doesn't account for all the differences you have noted. There are other factors: boiloff rate (which is dependent largely on kettle dimensions and the vigor of your boil), the amount of water retention in the grain and hops, etc.

Once you have a handle on the volumes used in your process, you can dial in those values in the equipment profiles in BS to more accurately predict it in future brews. You can do the same in your spreadsheet. By taking measurements along the way in each brew and adjusting the rates accordingly, you should be able to get your spreadsheet and BS to closely track.
 
The mash volume for BIAB is pretty straightforward. It would be the water needed for the boil plus the grain absorption and then add in any losses from the mash. That would give you the total water needed in the mash.
 
Okay - i'm finally asking the question(s) that i should have when first starting to BIAB.

I have a straightforward excel spread sheet which computes required mash volume taking inputs (desired fermenter volume, lbs of grain, shrinkage, quantity of hops, boil losses). For this recipe: 30.6 lbs grain, 11G into fermenter, 3.1 grain absorption, 1.5G boil loss, shrinkage computes to 16.2 Gallons required.
In BS - I enter comparable quantities and BS computes 18.3Gal.

I'd like to use BS to guide me on water adjustments, so getting mash volume is important - what am i missing?
thanks
You're simply missing that you need to know what happens in your brewery:). Brew a few batches, keeping your procedure strictly the same, and you'll need no calculator. You'll know how much fluid will be lost on the way, given the weight of the grist. Like Brad says, it's pretty straightforward - it just takes some trial and error. No way around that, I'm afraid:).
 
Try these. Everything starts with an accurate equipment profile and you can customize your own mash profiles too...


 
First thing to note is that BeerSmith calculated the water volumes for anything pre-fermenter as hot water. If your spreadsheet calculates based upon room temperature water, then you will need to account for the thermal expansion when comparing any numbers.

If you take a look at your recipe and go to the 'vols' tab, you can see the amount of water for each stage of the process. Compare these numbers to the ones you use in your spreadsheet. This will give you an idea of where you may need to look for adjustments in the BeerSmith parameters. Many of these parameters can be found in the 'options' > 'advanced' section of BeerSmith.
So, if in the "mash" tab it indicates, for example, "add 20 L at 70 C" I would have to, in practice, put a little less water at 20 C, to compensate for the thermal expansion? I ask because it is easier for me to measure the initial volume at room temperature.
 
Yes, the difference in volume between 20 C and 70C is about 2%, and the difference between 20 C and 100C is about 4%. So instead of adding 20 liters at 70C you would add 20/1.02 = 19.6 liters of water at 20 C.


--GF
 
So, if in the "mash" tab it indicates, for example, "add 20 L at 70 C" I would have to, in practice, put a little less water at 20 C, to compensate for the thermal expansion? I ask because it is easier for me to measure the initial volume at room temperature.
If you are using cold water (i.e. not heated up) you can do one of two things. You can take the volume BeerSmith calculates and divide that by 1.04 (assuming that your thermal expansion coefficient is set at 4%). My preference is to set the thermal expansion to 0% which will calculate all the volumes in BeerSmith at room temperature. Since I do full volume BIAB and measure my water and ending wort cold, it works out for me. I still need to convert my pre-boil volume measurement from the hot volume to room temperature volume, but that is secondary and done to check the efficiency.
 
Oops! What I posted was correct about the expansion of water, but I forgot the BeerSmith doesn't work that way. It uses only the figures for cold water and boiling water, so Oginme is correct. You need to divide the BeerSmith number by 1.04, not 1.02. I do as he suggests and I set the thermal expansion to zero in BeerSmith and calculate manually if I need a post-mash or pre-boil volume.
 
Oops! What I posted was correct about the expansion of water, but I forgot the BeerSmith doesn't work that way. It uses only the figures for cold water and boiling water, so Oginme is correct. You need to divide the BeerSmith number by 1.04, not 1.02. I do as he suggests and I set the thermal expansion to zero in BeerSmith and calculate manually if I need a post-mash or pre-boil volume.
That is one of the reasons I use 0% for the thermal expansion. This puts the inbedded calculation error of BeerSmith in the volume and not in the gravity calculation. Since it treats the thermal expansion as an 'all-or-nothing' factor and uses the thermally expanded volume for the pre-mash gravity calculation, it gives a relatively minor error in the gravity target. Transferring the error to the volumes gives me an accurate gravity measurement and I can use the actual thermal expansion coefficient based upon the temperature of the wort for calculating my 'cool' wort volume.
 
Thanks for the explanations @Oginme and @GigaFemto. Now I have an accurate reference on the correct initial volume of water. Cheers!
 
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