Author Topic: Mash water calculation  (Read 603 times)

Offline amadest

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Mash water calculation
« on: October 27, 2021, 02:46:09 AM »
Hi there!

Don't know if something similary allready been asked but i think something in not right with total mash water calculation.
Let's presume following data is used:
Batch size 19l
Trub loss 1.5l
Boil off 3l
Grain weight 4l
Grain  absorption is 3.76l
Let's start

(19L+1.5l)/0.96=21.35l amount of wort after cooling (so far in line with calculation of Beersmith 3 software)
21.35+3=24.35l amount of wort before boil (so far in line with calculation of Beersmith 3 software).
But this is hot, expanded wort!!! So amount of cold wort is 24.35*0.96=23.38l
23.38+3.76=27.14l this is including grain absorption. But Beersmith 3 software calculation is 28.11L which is true in case i mash in with 100C water

PS. I suppose that I know answer to this - mashing in temperature is different every brew and is somethere in 60C-70C, not 20C. This asumption decrease difference in half but anyway this is half a liter in this particular sample which is quite an amount. :o 8)



Offline BeerSmith

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Re: Mash water calculation
« Reply #1 on: October 27, 2021, 11:32:17 AM »
Not sure of the exact question but the temperature will change a bit from batch to batch based on how much grain you have in the mash.

Brad
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Offline Oginme

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Re: Mash water calculation
« Reply #2 on: October 27, 2021, 01:38:38 PM »
Hi there!

Don't know if something similary allready been asked but i think something in not right with total mash water calculation.
Let's presume following data is used:
Batch size 19l
Trub loss 1.5l
Boil off 3l
Grain weight 4l
Grain  absorption is 3.76l
Let's start

(19L+1.5l)/0.96=21.35l amount of wort after cooling (so far in line with calculation of Beersmith 3 software)
21.35+3=24.35l amount of wort before boil (so far in line with calculation of Beersmith 3 software).
But this is hot, expanded wort!!! So amount of cold wort is 24.35*0.96=23.38l
23.38+3.76=27.14l this is including grain absorption. But Beersmith 3 software calculation is 28.11L which is true in case i mash in with 100C water

PS. I suppose that I know answer to this - mashing in temperature is different every brew and is somethere in 60C-70C, not 20C. This asumption decrease difference in half but anyway this is half a liter in this particular sample which is quite an amount. :o 8)

Let us start with the fact that BeerSmith uses the thermal expansion as a fixed percentage and does not scale that according to temperature.

Next, you can follow the volumes on the 'vols' tab of your recipe.  It does start at the bottom with the Volume to fermenter (batch size) and trub loss.  From there it calculates up.

It takes the amount of process trub (cold value) and adds that to the cold volume needed at the end of the boil.  It will then apply the expansion factor to get the amount of hot volume.  From that point up, all the volumes are considered HOT and expanded at the volume of your thermal expansion.

In your case, the cold volume at the end of the boil is 19 L of wort in the fermenter and 1.5 L of process trub which leaves 20.5 L of cold wort.  The thermal expansion coefficient you have set to 4%, so add 4% x 20.5 L or 0.85 L which then gives you 21.35 L of hot wort at the end of the boil.

You boiled off 3 L of volume so that leaves your pre-boil volume to 24.35 L. 

You do not state if you have any mash tun losses, so I am assuming 0 L for this value. 

Your grain absorption is 3.76 L, which gives a total volume of water needed at 28.11 L of HOT water.   As stated before, the program assumes that this is at boiling temperatures so there is a built in overage in the calculation if you are measuring at normal strike water temperatures.  At typical strike temperatures, the actual thermal expansion is about 1.8% to 2% (because it is non-linear), so if you are measuring your water at strike temperature, you can expect a 2% to 2.2% error in your actual volume versus BeerSmith.

If you are using cold water (I do since I use an Anvil Foundry), you can set the thermal expansion to zero and you will get the amount of cold water to measure in.  So I measure about 15.2 L to 15.8 L depending upon grain bill and go from there.  I measure and record the hot volume after the mash, but since I have the system balanced in pretty well, I can count on having 10 liters into the fermenter and a liter of wort left behind (cold volumes) and everything balances out just fine.

Alternatively, if you are looking to be more accurate at mash temperatures, you can set your thermal expansion to 2.0 and do your measurement using the heated water. 

Remember the software is a tool for you to use and adjust as needed to fit your needs.  Once you get your equipment profile accurate enough to give you predictable gravity and volumes at the end of the boil, should be set.
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Offline amadest

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Re: Mash water calculation
« Reply #3 on: October 30, 2021, 12:30:12 AM »
Thanks a lot, Oginme! Now I know that program takes hot water in calculations.

 

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