Volume lost to boil thrub and chiller...??

Hi. I'm having a hard time figuring out how beersmith handles volumes, particularly volume lost to boil thrub and chiller. It seems entering a number here will change calculated OG and IBU's?

To exemplify my problem...

Say I brew 2 identical brews, efficiency set to 80%, 5.43 kg pale ale malt, 13% evaporation, 0 top up water, 31 liters preboil volume.

Brew 1  - I decide to dump all thrub in the fermentor and thus get 26 liters in the fermentor , Beesmith predicts OG of 1.050 (which is typically close to my actual numbers)

Brew 2  - Exactly the same as brew 1 except this time I leave all thrub in the kettle (say 7 liters...) This leaves me with 19 liters in the fermentor, 7 liters lost to thrub and a preboilvolume of 31 liters. If I plug in 19 liters batch size (what I get in the fermentor) and 7 liters lost to thrub, I get 31 liter preboil volume (correct) and and OG of 1.068 (incorrect). IBU and color calc. are off too..

Surly the amount of thrub/wort left in the kettle should not change OG or IBU of the beer? So what I'm guessing is beersmith bases calculations on "batch size", but should calculations not be based on batch size+Volume lost to boil thrub and chiller?
Or am I not thinking correctly?

The IBU estimations are based on boil size, so if you change the trub loss it can change the starting boil size if automatically calculated.  Particularly if you lose a lot of wort, you will actually have less IBUs in the finished beer than a comparable beer with no losses.

Cheers,
Brad

Well... if the two beers are brewed identical, the preboil volume of both beers will be the same (since the same mash/sparge is used). So I still dont get how leaving more thrub in the kettle should change SG or IBU's... ???

BeerSmith said:

The IBU estimations are based on boil size, so if you change the trub loss it can change the starting boil size if automatically calculated.  Particularly if you lose a lot of wort, you will actually have less IBUs in the finished beer than a comparable beer with no losses. Cheers, Brad

Click to expand...

Brad - I understand how the hops utilization models typically use the boil gravity and time to calculate the Util Factor in their formulas.  So, if you planned a recipe with 7 gallons pre-boil of 1.050 wort, you'd get a certain IBU estimate from Tinseth/Rager/BSmith after the appropriate Util Factors were applied to each hop addition.  And if you then failed to collect that volume, or reached a different pre-boil gravity (higher or lower) you'd get a different actual utilization than originally forecast because a different Util Factor would be applied to each hop addition. 

However, "trub loss" that is left in the kettle by choice happens at the end of the boil, and it should have the same effect on my utilization as if I mistakenly spilled it on the floor.  The wort is done, and spilling it doesn't effect the amount of IBUs in the wort. 

The boil gravity, the volume, and the subsequent hop additions all went (let's assume) according to recipe.  The only thing that happened was some wort didn't reach the fermenter. 

Vitkske - I allow for 1.25 gallons loss in the bottom of my keg/boiler, and I changed that to zero, and it did not change the estimated OG or IBUs.  It just changed my boil volume, logically, so I don't end up short.

I think the difference is that you're changing the batch size from 26L to 19L, and most of those estimated calculations are based on batch size.  If you're 'choosing' to lose those 7L to trub/clarity (as I do), you have to tell BSmith that in advance so it can tell you to use more water/grains/hops to get the final product you want.  Otherwise, it is like spilling it, and BSmith cannot predict that. 

Try tinkering with it while keeping the batch size at 26L.  You made that much wort, so you have to take credit for it all.  Just tell BSmith how much you're leaving behind for clarity's sake, and it will tell you how much to start with.  From there it will apply the appropriate hops Util Factors, evap rate losses, etc. to reach the final SG and IBUs, and volume. 

MaltLicker said:

However, "trub loss" that is left in the kettle by choice happens at the end of the boil, and it should have the same effect on my utilization as if I mistakenly spilled it on the floor.  The wort is done, and spilling it doesn't effect the amount of IBUs in the wort. 

Click to expand...

That was my thinking too.

But yes, I was changing batch size from 26L to 19L  between to brews that were equal i volume. I wanted to experiment with dumping all thrub in the fermentor vs. leaving all thrub in the boil kettle. I guess I need to keep the batch size at 26L and set "loss to thrub" to zero and manually account for any losses to thrub. This is because in the case of "a lot of thrub left behind in the kettle" I would prefer end up with a smaller fermentable volume rather than a larger preboil volume (which is limited by my kettle size...).