Author Topic: Volumes/Temperatures/Grain Absorption  (Read 1551 times)

Offline pennengr

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Volumes/Temperatures/Grain Absorption
« on: December 24, 2020, 11:30:07 AM »
Hi - I've started using some new equipment, and had some unexpected numbers on my last brew, so I'm trying to dig into the math a bit.

Total Mash Water: 10.13 gal @ 157 F
Grain: 12.24 lb
Grain Absorption: set @ 0.85 fl oz/oz ==> 1.30 gal

BeerSmith tells me that the water available from the mash should be 8.82 gallons - which makes sense I think @ mash temperature (10.13 gal - 1.30 gal = 8.83 gal).

If I take the 8.82 post mash number and adjust it for temperature, I calculate 8.82 gal * (8.17 lb/gal @ 155 / 8.00 lb/gal @ 212) = 9.01 gal preboil.

But then my estimated pre-boil volume is also 8.82 gal.  I would have thought that this would have been at boiling temperatures, as the math for boiloff and cooling shrinkage seems to work out exactly.

Ultimately I'm trying to back-calculate a measured grain absorption so that I can adjust, but the temperatures for the volumes have me scratching my head as well.

Can anyone point me in the right direction here?
  • Is the "Water Available from Mash" field @ mash temperature?
  • Is the "Estimated Pre-Boil Volume" field @ boiling temperature?
  • What measurements (at what temperatures) do I need to calculate actual grain absorption?

I've looked through the documentation and forum and had trouble finding an answer. Thanks.

Offline Oginme

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Re: Volumes/Temperatures/Grain Absorption
« Reply #1 on: December 24, 2020, 12:25:52 PM »
The program uses one value for the thermal expansion of water.  It does not scale it based upon the temperature.  This value can be found in your equipment profile (cooling shrinkage %) and you can adjust it to fit your conditions.  I was using 2.2% when I used a mash tun, since I measured my post mash volume right after draining the mash tun and not at boiling.  When I switched to full volume BIAB, I changed it to 0%, because the most important measurements Water in and fermenter volume were both at room temperature.  The one value measured hot was post mash volume and I could easily figure out the value for thermal expansion to ball park the measurement versus the cold volume the program had as a target.

This thermal expanded volume is also used to estimate the gravity from the mash using the gravity points calculated from the fermenter and process trub losses.  Since this value is a cold volume, it underestimates the gravity target from the mash.  Using the 0% expansion, when I hit my mash gravity target, I always hit my fermenter gravity target.  My volumes are usually within 100 ml of the target 11 liters post boil volume (cold), so everything works out correctly in the end.

Recycle your grains, feed them to a goat!

Offline pennengr

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Re: Volumes/Temperatures/Grain Absorption
« Reply #2 on: December 24, 2020, 01:26:04 PM »
Oginme,

Thank you for the response.  I've been brewing (full volume) BIAB for a number of years and have just shifted to a Spike Solo basket but I'm still doing full volume.

My settings had been defaulted to 4% cooling losses.  I was calculating a room temperature mash water addition based on the required mash temperature addition (using real densities).  For this example, 9.9 gal @ RT to get to 10.1 gal @ 157, then targeting a post-mash volume based on the required 8.82 gal pre-boil volume (again with some of my own temperature calculations = 8.63 gal @ 157).

If I shift to a 0% cooling shrinkage, BS tells me to use 9.85 gallons of water at 157, and lists a preboil volume of 8.55 gal.  From a process standpoint, I would use 9.85 gal @ room temperature, and do my own offline estimates of post-mash and pre-boil volumes @ mash and boil temperatures respectively to adjust volume if needed (but trust the s.g.), and the numbers should work out?

And if I wanted to measure actual grain absorption, just capture the actual observed at the end of the mash (@ mash temp) and manually calculate the room temp value?

Thanks.

Offline Oginme

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Re: Volumes/Temperatures/Grain Absorption
« Reply #3 on: December 24, 2020, 01:59:17 PM »


If I shift to a 0% cooling shrinkage, BS tells me to use 9.85 gallons of water at 157, and lists a preboil volume of 8.55 gal.  From a process standpoint, I would use 9.85 gal @ room temperature, and do my own offline estimates of post-mash and pre-boil volumes @ mash and boil temperatures respectively to adjust volume if needed (but trust the s.g.), and the numbers should work out?

And if I wanted to measure actual grain absorption, just capture the actual observed at the end of the mash (@ mash temp) and manually calculate the room temp value?

Thanks.

Because the program does not scale the thermal expansion, you are correct.  What this will do is give you an accurate estimated post mash gravity target.  At 157F, you are looking at around a 2.2% thermal expansion from room temperature, so you can just figure on being a little over the estimated pre-boil volume.  With a 0% thermal expansion, you can calculate the grain absorption by taking the hot volume reading and correcting it back to room temperature.  The difference between the starting volume and temperature corrected pre-boil volume is your grain absorption volume.  Since all your volumes are calculated based upon a volume corrected to room temperature, the grain absorption should be calculated at this same standard temperature. 

If there are any questions on the measurements, I run a gravity point balance pre-boil to post boil which typically comes out within +/- 0.1% error. It also helps pick up any process issues pretty quickly.

Recycle your grains, feed them to a goat!

Offline pennengr

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Re: Volumes/Temperatures/Grain Absorption
« Reply #4 on: December 24, 2020, 04:03:33 PM »
Great - appreciate the help.

 

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