Puzzle: Volume<->Gravity calculation Beersmith vs reality

[Suicid]

Hi folks,

Can you please help me to solve following puzzle:
I'm routinely using Beersmith for my AG brews and it is not the 1st time I met a strange situation which kinda contradict with my broken logic.

Lets say Beersmith calculated
Preboil volume 27L
Preboil gravity 1.043
Postboil volume 23L
Postboil SG 1.053

I missed preboil volume and collected 28L
Same time I measured SG of this wort (28L) - it was 1.047 -> 4 points higher than calculated
Ok

I have 4L/h evaporation rate so I adjusted my biol time to 1h 15min and carried on.
Got postboil volume 23l exactly.
Measured gravity - guess what? 1.053

To my understanding, I had both volume 1L more and SG 4 points higher than calculated values.
So boiling down to calculated volume should give me 1.057 (28L*47points/23L), but it is not.

Are BS calculation off there and what could be the reason of that?

 

[AdjunctBrewer]

I'm not a Beersmith user but there are many settings for volume in the equipment and water volume profiles. Also check that the grain absorbtion rate is set correctly.

The Brewers Friend Dilution and Boil Off calculator is more straight forward math similar to what you did.

https://www.brewersfriend.com/dilution-and-boiloff-gravity-calculator/

 

[DBhomebrew]

Are you adjusting volumes for temperature? Is the software?

How accurate are your volumetric measurements? Are you looking at a scale on the side of the kettle marked every quart/liter?

How accurate are your gravity measurements? Are they adjusted for temperature? Are you letting your sample cool? If so, is it covered to prevent evaporation?

There are plenty of other possibilities.

 

[Suicid]

There are plenty of other possibilities.

Thats true.

Volume measured with a calibrated SS yardstick, SG - with ATC refractometer.

But still to me its hard to explain to myself how can I get wrong readings with the same yardstick and the same refractometer.

In any cases (exact numbers aside) and by plain logic: more (than calculated) volume + higher (than calculated) SG wort boiled down to **calculated** volume SHOULD have higher than calculated SG.
But it does not.

And I'm pretty sure it is not because my refractometer can measure SG correctly only up to 1.050 or so

And moreover: I have pretty much spot on equipment profile and ingredients properties dialed into Beersmith. And if everything goes well usually calculated values are perfect match with readings. This fact confusing me even more.

 

[doug293cz]

The following equation should hold between pre and post-boil measurements:

Pre-boil volume * (Pre-boil SG - 1) = Post-boil volume * (Post-boil SG - 1)​

​

If we plug in a pre-boil volume of 27.0 L, pre-boil SG of 1.043, and a post-boil volume of 23.0 L, then the post-boil SG calculates out to 1.0505. So, it looks like there is something funky going on in BeerSmith. It might just be rounding errors. If we say pre-boil volume was actually 27.45 L, pre-boil SG of 1.0434, and post-boil volume of 22.55 L (all values which round to the original inputs), then the calculated post-boil SG would be 1.0528 which rounds to 1.053. This demonstrates how small errors in measurements can result in significant errors in calculated results.

If we run the check calculation on your actual measurements (28 L @ 1.047 -> 23 L), the predicted post-boil SG works out to 1.057.

If you sparge, then another source of potential error is failure to fully homogenize the first running wort and sparged wort. Any stratification in the pre-boil wort can lead to either erroneously high or low SG measurements depending on whether you sampled from an extract rich or extract lean zone of the wort volume.

Brew on

 

[Suicid]

The following equation should hold between pre and post-boil measurements:

Pre-boil volume * (Pre-boil SG - 1) = Post-boil volume * (Post-boil SG - 1)​

​

If we plug in a pre-boil volume of 27.0 L, pre-boil SG of 1.043, and a post-boil volume of 23.0 L, then the post-boil SG calculates out to 1.0505. So, it looks like there is something funky going on in BeerSmith. It might just be rounding errors. If we say pre-boil volume was actually 27.45 L, pre-boil SG of 1.0434, and post-boil volume of 22.55 L (all values which round to the original inputs), then the calculated post-boil SG would be 1.0528 which rounds to 1.053. This demonstrates how small errors in measurements can result in significant errors in calculated results.

If we run the check calculation on your actual measurements (28 L @ 1.047 -> 23 L), the predicted post-boil SG works out to 1.057.

If you sparge, then another source of potential error is failure to fully homogenize the first running wort and sparged wort. Any stratification in the pre-boil wort can lead to either erroneously high or low SG measurements depending on whether you sampled from an extract rich or extract lean zone of the wort volume.

Brew on

Oh! You right!
Thanks alot, it explains everything.

Cheers!

 

[Bobby_M]

Two ideas. Preboil wort stratified. Stir a bit before pullng sample.

Wort samples flash evaporating on the refractometer. Shake the bulb of your pipette in ice water for 10 seconds.

 

[Broothru]

The following equation should hold between pre and post-boil measurements:

Pre-boil volume * (Pre-boil SG - 1) = Post-boil volume * (Post-boil SG - 1)​

​

If we plug in a pre-boil volume of 27.0 L, pre-boil SG of 1.043, and a post-boil volume of 23.0 L, then the post-boil SG calculates out to 1.0505. So, it looks like there is something funky going on in BeerSmith. It might just be rounding errors. If we say pre-boil volume was actually 27.45 L, pre-boil SG of 1.0434, and post-boil volume of 22.55 L (all values which round to the original inputs), then the calculated post-boil SG would be 1.0528 which rounds to 1.053. This demonstrates how small errors in measurements can result in significant errors in calculated results.

If we run the check calculation on your actual measurements (28 L @ 1.047 -> 23 L), the predicted post-boil SG works out to 1.057.

If you sparge, then another source of potential error is failure to fully homogenize the first running wort and sparged wort. Any stratification in the pre-boil wort can lead to either erroneously high or low SG measurements depending on whether you sampled from an extract rich or extract lean zone of the wort volume.

Brew on

The efficiency calculations are totally dependent on the accuracy of the volumetric measurements. I no longer even consider the numbers output by BeerSmith on predictive ABV and mash efficiencies. My mash volumes are constant and, based on my grain bills, I can very accurately predict my OGs. I could probably fine tune my BS inputs, but why go to bother? I intuitively know what my OGs will be, notwithstanding what BreeSmith predicts.

I’m usually higher on efficiency and OG than BS predictions, and my ABVs (prediction) are generally within 1~2 points of my actual values as derived from EasyDens, which is very accurate.

 

[day_trippr]

Otoh, I tuned a set of BeerSmith mash profiles to account for low, medium, and high hopped recipes, on top of my highly tuned equipment profiles, such that I reliably end up with two kegs filled within a cup of 5 full gallons each and with OG and FG predictions within a point of actual outcomes. It's become rote to nail all those metrics...

Cheers!

 

[JohnDBrewer]

I’m usually higher on efficiency and OG than BS predictions

Isn't efficiency one the inputs you put in?

 

[kevin58]

It is imperative that you customize your equipment profile(s) when using Beersmith. Everything relies on that. Watch the video link below and take actual measurements as you go. Even then you will want to take real world measurements during your brew day and use those to tweak that equipment profile until you get it dialed in.

As @day_trippr suggests you will also want to create profiles for differing situations. Staying with the equipment profile you may want to create a separate one with lower mash efficiencies built in for brewing high gravity beers using larger grain bills. I have created my own mash profiles following Marshall Schott's video also linked below.

Beersmith's success is highly dependent on user input. If you take the time to tune your profiles it will work with a high degree of dependability. If not you can expect frustration every brew day.



https://brulosophy.com/2014/08/11/beersmith-tutorial-biab-mash-profile-setup/

 

[Broothru]

Isn't efficiency one the inputs you put in?

Actually, efficiency is one of the outputs in BeerSmith that gets inserted into the Design tab from the Session tab.

 

[doug293cz]

Actually, efficiency is one of the outputs in BeerSmith that gets inserted into the Design tab from the Session tab.

To be totally accurate, BS requires you to input your estimated Brewhouse Efficiency. BS then calculates your estimated mash efficiency using the following equation:

Mash Efficiency = Brewhouse Efficiency * (Batch Volume + Loss to Trub and Chiller) / Batch Volume​

​

It is up to the brewer to make adjustments to their brewhouse efficiency input that take into account changes in lauter efficiency with different size grain bills. This is actually not a very good way to do things, as it is relatively straight forward to predict lauter efficiency based on grain bill, pre-boil volume, grain absorption rate, MLT undrainable volume, and sparge process specifics. The brewer would then only be responsible for inputting their typical conversion efficiency, which should not depend on the batch specifics (unlike brewhouse efficiency.)

When you input your actual batch data (volume and SG measurements) BS then uses those to calculate your actual mash efficiency.

Brew on

 

[JohnDBrewer]

Actually, efficiency is one of the outputs in BeerSmith that gets inserted into the Design tab from the Session tab.

You're right, there are two efficiencies, brewhouse and mash. If your brewhouse is not correct, your OG and other estimates won't be either. I adjust my BH efficiency every batch, as soon as I get my preboil gravity. So if my original estimated preboil says 1.043 and I come in at 1.047, I change my brewhouse efficiency to until my estimate match.