Author Topic: Beer smith volume confusion  (Read 3891 times)

Offline jakubdudek

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Beer smith volume confusion
« on: April 06, 2020, 11:23:54 PM »
Greetings!

I need some help understanding what beersmith is doing with volumes.  I am tinkering with it and trying to setup a simple example.  I do full volume BIAB mash, so to obtain 5.5 gallons into the fermenter, assuming 0.5 gallons absorbed in grain and 1 gallon boiled off, I expect my starting mash water to be 7 gallons.

I setup the absortion rate in the options and the boil off rate in the equipment.

Beersmith says 7.25 gallons to start.  The discrepency appears to be the cooling shrinkage, which is 0.23.  With the calculated 0.52 gallon absorbed by the grain, the 0.23 difference is exact.



If this is the case, it makes no sense to me.  The initial volume is at room temperature... the volume difference is "gained" heating and "lost" during cooling.  It should have no bearing on initial volume at room temperature.

or, is something else going on i don't understand?

Thanks much!
-Jakub

Offline Oginme

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Re: Beer smith volume confusion
« Reply #1 on: April 07, 2020, 02:46:09 AM »
If you look at the volume tab in a recipe, you can follow the volume calculations backward.  The fermenter volume is at a cold temperature and the program adds the losses for trub.  It then inflates the volume to account for the thermal expansion (cooling shrinkage) and never adjusts the volume back to a cold measurement.  It will then give the initial strike volume as a hot value, already thermally expanded by the thermal expansion coefficient in the equipment profile.

You can set the thermal expansion to 0% and your initial strike water will then reflect a cold water volume.  This will then result in your pre-boil volumes being off by the expansion at mash out or near boiling temperature (depending upon when you take your volume measurement) so you will find your mash efficiency calculation slightly over-inflated.

Alternatively, you can take the value BeerSmith starts with and divide this by 1 plus your expansion coefficient (i.e. 4% would give you 1.04) to get a room temperature volume for measuring out your water.
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Offline jakubdudek

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Re: Beer smith volume confusion
« Reply #2 on: April 07, 2020, 09:03:35 AM »
Thanks for the clarification. Seems very strange to me that beersmith doesn?t tell you how much water to pour in your kettle. Step 1 of the brew day... I?m not sure I see the purpose of a heat expanded initial volume. Unless you?re transferring out of the HLT I guess...

Offline Kevin58

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Re: Beer smith volume confusion
« Reply #3 on: April 07, 2020, 03:33:59 PM »
I admit that I usually scroll right on past these cooling shrinkage discussions because, not to crude but, I just don't care. That is to say that the differences talked about seem so small as to make not enough difference for me to worry about. With that in mind please ignore me if I am not understanding the issue in this case. You are expecting a 7 gallon initial volume and the software is telling you its a quarter gallon more. To me that's not enough to bother with.

I did notice however that you said you assumed 0.5 gallons absorbed by the grain. If you really want to get better results from the software you really need to take accurate measurement to create both your equipment and mash profiles. Take actual measurement of all your volumes in and out. That includes losses in pumps and hoses, chillers (counter flow or plate chillers for example) and measuring your boil off rate too. If you use guesses to make those profiles you can't expect pinpoint results.
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Offline jakubdudek

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Re: Beer smith volume confusion
« Reply #4 on: April 07, 2020, 10:43:23 PM »
Hi Kevin,

the "assumed" grain absorption here was to construct a simple example to illustrate who beer smith gives me a starting volume different than what i expected.  In real life, as you said, i measured actual volumes and grain absorption, boil off etc (not many other losses I do BIAB).  My point was only to illustrate that if you lose 0.5 gallons and 1 gallon to boil off and want 5.5 gallon into the fermenter then the correct starting volume is 7 gallons.  Beersmith says 7.25.  It's now understood why, even though it seems to me a funny idea to include heat expansion in initial volume.

In my simple example, an extra 0.25 gallons at the start would yield an OG 4 points below target.  Not the end of the world sure, but i enjoy fine tuning and hitting targets.  While I understand why many people glance over this as unimportant, to me it's part of the fun.

Offline brewfun

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Re: Beer smith volume confusion
« Reply #5 on: April 08, 2020, 06:45:02 AM »
My point was only to illustrate that if you lose 0.5 gallons and 1 gallon to boil off and want 5.5 gallon into the fermenter then the correct starting volume is 7 gallons.  Beersmith says 7.25.  It's now understood why, even though it seems to me a funny idea to include heat expansion in initial volume.

The simple fact is that most people measure volumes hot, so it's best if it's consistent that way. Accuracy is really achieved by weight, rather than volume. However, few (if any) homebrew systems have load scales.  ;) 

Quote
While I understand why many people glance over this as unimportant, to me it's part of the fun.

Agreed, it's part of the fun for me, too. There's a gravity error in BeerSmith based on that very expansion issue that's been there in every version. Once you know that, it's easy to just ignore it and build it into the pre boil gravity (making post boil accurate). Actual measured gravity will be a bit more than the prediction.

For work, I use several programs for brewing. Honestly, compared to programs that cost hundreds per month, BeerSmith still manages recipe formulation best. The "pro" programs are really about accounting and logistics.
Beer Appreciation is the space between pints.