Help - BS not accounting for gravity lost in trub?

Hello Beersmithers,

I got BS mobile and used it for my last batch. Overall, I love the software and thought that it very accurately predicted my volumes. I was a bit concerned with how far off my OG was from the predicted gravity, and decided to run it by my now "old school" calculations a la past batches.

In summary, (and given the huge disclaimer that I may not be programming it properly) I believe that BS might be overestimating OG by not correcting for points lost in kettle trub.

Just by calculating how many potential points (not per gallon, and not factoring BHE), I determined that my batch should have had 624 potential points total.  Postboil (and post-cooling volume), my volume should be (and was!) 5.5 gallons. For this batch, I was transferring 4.5 gallons wort into the fermenter, therefor 1.0 gallon trub was predicted to be remaining in the fermenter. I determined that according to BS, my OG was calculated by taking 624 and dividing it by fermenter batch volume, and not my postboil volume. By doing this, the points/volume was higher than it should be, resulting in an overestimation of my OG.

Does anyone know how I should solve this? I attempted to search around the forums to find some resolve, but I was [obviously] unsuccessful. If someone could point me to the correct forum, I'd be really appreciative.

Thanks!

Jeff2184 said:

I determined that according to BS, my OG was calculated by taking 624 and dividing it by fermenter batch volume, and not my postboil volume. By doing this, the points/volume was higher than it should be, resulting in an overestimation of my OG.

Click to expand...

That is what BS2 does.  I believe BS2 runs most calcs on Batch Volume, which is the target volume going into fermenter.  All expected losses must be entered prior to brewing so that BS2 knows that some gravity points aren't making it to the fermenter. 

Had you had entered the 1.0 gallon "Loss to trub and chiller" before brewing?  And Batch Volume was set to 4.5 gallons?  If not, start with Batch Volume at 4.5 and add back all expected losses to that.  That tells BS2 (and the brewer) what to start with to reach the goal, IF all goes to plan. 

Thank you for your response.

Yes, I have added 1.0 gallon to the trub loss. The issue that I am having is because BS calculates based on the batch volume, and not the post-boil volume, my OG will be lower than it should be. To give some more details for a 5 gal batch:

with 624 max potential points going into this batch, BS looks at my batch vol (5 gallons) and figures my OG should be 1.087 after a 70% brew-house efficiency.

624pts/5gal = 124.8 pts/gal
124.8pts/gal * 70% BHE = 87.36pts/gal, or a 1.087 sg

(if at this point you are wondering why I say 4.5 gal batch vol in the last post and 5 gal here, its just because I "fermenter top off water" 0.5 gallons for this batch in fruit, but as far as BS is concerned this is just water)

My actual OG was around 1.076, which wasn't terribly off my mark, but:

the actual concentration of my wort was 124.8 max potential points in 5.5 gallons. This puts my postboil gravity, assuming wort has cooled to appropriate volume (with 70% BHE at) 1.079.

624pts/5.5gal = 113.45 pts/gal
113.45pts/gal * 70% BHE = 79.4pts/gal, or 1.079

I understand that the OG of the trub is likely not exactly the same as my wort, but I should not expect that it contains no sugars(?).

Just for kicks, I set my loss to trub value to 10 gallons (keeping to a 4.5 gallon batch) and the predicted OG remained at 1.087 (and grain bill remaining at 624 points). This clearly would not be accurate, because if I took 624 points into 14.5 gallons (ignoring BHE) my postboil concentration would be 43 points/gallon, regardless of how much wort is transferred into a fermenter.

Any thoughts?

Jeff2184 said:

with 624 max potential points going into this batch, BS looks at my batch vol (5 gallons) and figures my OG should be 1.087 after a 70% brew-house efficiency.

624pts/5gal = 124.8 pts/gal
124.8pts/gal * 70% BHE = 87.36pts/gal, or a 1.087 sg

(if at this point you are wondering why I say 4.5 gal batch vol in the last post and 5 gal here, its just because I "fermenter top off water" 0.5 gallons for this batch in fruit, but as far as BS is concerned this is just water)

My actual OG was around 1.076, which wasn't terribly off my mark, but:

the actual concentration of my wort was 124.8 max potential points in 5.5 gallons. This puts my postboil gravity, assuming wort has cooled to appropriate volume (with 70% BHE at) 1.079.

624pts/5.5gal = 113.45 pts/gal
113.45pts/gal * 70% BHE = 79.4pts/gal, or 1.079

I understand that the OG of the trub is likely not exactly the same as my wort, but I should not expect that it contains no sugars(?).

Just for kicks, I set my loss to trub value to 10 gallons (keeping to a 4.5 gallon batch) and the predicted OG remained at 1.087 (and grain bill remaining at 624 points). This clearly would not be accurate, because if I took 624 points into 14.5 gallons (ignoring BHE) my postboil concentration would be 43 points/gallon, regardless of how much wort is transferred into a fermenter.

Any thoughts?

Click to expand...

I don't understand the usage of two sets of numbers.  BS2 is built on Batch Volume.  You and BS2 have to work with the same assumptions.  Was the batch size entered into BS2 4.5, 5.0 or 5.5?  That's the only batch size that really matters. 

BS2 is not a great "what-if" scenario manager.    It's more a "planning" software package.  It's best use, IMO, is to enter the best-guess estimate of the brewing plan, and then after the brew, enter what really happened.   

If everything went to plan, and you got either more OG or less than estimated, then you're dialing in your system.  And you will estimate better next time. 

If something went awry that you won't repeat, then maybe you only learned process tweaks, and perhaps not anything that you'd change in BS2. 

Thank you again for your response. I have a feeling that I might be doing something wrong. Let's forget the last examples all together and just talk about a more simple scenario.

I end a boil with 6 gallons after cooling. Due to trub loss, 1 gallon will not make it to the fermenter. 5 gallons going into the fermenter is my "batch volume" and 1 gallon is marked as "trub loss".

In this 6 gallon postboil volume I have 600 total potential points. My hydrometer would read 1.100, because 600pts/6gal = 100pts/gal or 1.100 sg. If I transfer 5 gallons of this to the fermenter, the fermenter batch gravity should also be 1.100.

I believe that what bs is doing here is calculating that I should have 600 potential points postboil, and then considering my 5gallon "batch vol", and calculating my og by taking 600pts/5gal = 120 points/gallon or an og of 1.200.

Unfortunately this calculation is independent of what the user selects as their trub loss volume. You can test this simply by keeping your grain bill the same and significantly increasing your trub loss variable. Your water volumes will correctly go up to match, but your predicted gravity will remain the same. This is where I am lost. I do not see how the batch volume is more important than postboil volume for determining original gravity.

Jeff2184 said:

In this 6 gallon postboil volume I have 600 total potential points.

Click to expand...

Does BS2 agree with you on this calculation?  I think perhaps you're co-mingling your independent calculations with BS2 math.  Or comparing them when that is not necessarily comparing apples to apples. 

Jeff2184 said:

I do not see how the batch volume is more important than postboil volume for determining original gravity.

Click to expand...

The PPG we can get from grains is very much a "concentration" calculation.  Potential Points per Gallon, so even if you are very efficient at lautering the sugars out (i.e., post-boil volume), but routinely lose liquid before reaching the final destination, you have to make the full six gallons at the desired concentration (i.e., OG) and be ready to sacrifice it.  Or spill it. 

The scenario closest to what you're describing is a stove-top brewer that cools and then pours the entire pot of wort thru a funnel into the carboy.  In that case, Post-Boil Volume would equal Batch Volume every time with no losses.  Every drop of PPG collected and boiled ends up in the carboy. 

Totally different analogy.......a house painter needs a 5-gallon bucket of paint to do the job.  The next job is bigger, and he's got just the same 5-gallon bucket.  The only way to do the job is to water down, i.e., weaken, the concentration of the paint.    He proceeds, and paints a Bud Light room.    The next room is a small bathroom, he still uses 5-gallons and paints a Dopplebock room.  Same PPG points in all three buckets (post-boil volume), but what really matters is how that initial volume ultimately gets spread across the final Batch Volume.

Jeff2184 said:

Unfortunately this calculation is independent of what the user selects as their trub loss volume. You can test this simply by keeping your grain bill the same and significantly increasing your trub loss variable. Your water volumes will correctly go up to match, but your predicted gravity will remain the same. This is where I am lost. I do not see how the batch volume is more important than postboil volume for determining original gravity.

Click to expand...

You're correct. In the desktop version, adding trub loss volume only increases the expected mash efficiency. The intuitive expectation is that that additional volume should lower both preboil and post boil gravities, since mash efficiency never magically increases.

This is a known flaw in BeerSmith. The solution has been to set the trub loss field to 0 and view the Batch size as the sum of yield and trub loss.

Thank you brewfun and maltlicker for your help!