Hopshot IBU Calculations in Beersmith 3

I'm having an issue getting the correct IBU calculation for an addition of Hopshots to my recipe. I need ~80 IBU's.

According to the Hopshot .pdf instructions, for 5 gallons of a 1.050 SG wort, 8ml is needed to hit 80 IBU's with a 60 minute boil. I'm building a Wort that should come in around ~1.080, so the pdf says to add 10%. That means I should add 8.8ml.

When I load Hopshot into my recipe, it originally wanted 23mL to get to 80 IBU's!! Then I realized for some reason the Hopshot was defaulting to an alpha level of 10%. According to Brad Smith's blog, is should probably be set to about 65%.

So, I've updated the alpha acids to 65% but it still wants me to add almost 16mL's.

So what am I missing??
I've uploaded my bsmx file (this recipe is in draft), if this helps.

Thanks,
Bob

I'm going to take a stab at this after looking at the hopshot information sheet.  I have not used AA extracts so I am going strictly by what I see in the sheets and from your comments.  Others may have a better take on this.

Based upon the sheet for hopshot, the IBU vs gravity chart appears to be referencing the Rager IBU formula.  It does not state that specifically, but the step increase in IBU at certain gravity steps is very indicative of the IBU curve derived from using the Rager formula.  AA utilization does not stay level from 1.030 up to 1.070 and then suddenly jump up at 1.080 and stay steady to 1.100  If this is what you use for your calculations, then you can probably go by these numbers.  If like most of the home brewing community, you use the Tinseth IBU model, then you might want to rethink their recommendations.  Given that, their recommendation of a 10% increase is based upon that step change.

If you do use the Tinseth formulation, the decrease in utilization from 1.060 to 1.080 is more on the order of 16.5%.  Just looking at your recipe and calculating the IBU based upon the Rager, I come up with around 83 IBU for your recipe as written. 

These recommendations also do not take into account any process losses.  You have 0.75 gal of losses between the end of boil and the fermenter, so the amount of wort you are treating is not 5 gallons but 5.75 gallons.  This will have an effect on the calculations as well.

Now, none of the models were ever intended to take into account the utilization of alpha acids from extracts.  So this becomes another point where the models, no matter which one, may be grossly off from reality. 

[stepping up on soap box]  There are serious questions about the relationship of calculated IBU to actual tested IBU let alone perceived bitterness.  Unfortunately it is the only tool we have to help define bitterness when designing a recipe, so we are kind of stuck with it.  And it does help some with trying to maintain some consistency within your process from brew to brew.  Just don't hang too much on the results reflecting your actual bitterness levels until you are comfortable with how the results reflect your expectations.  [stepping down now]

Thanks for your help on this. Rager and Tinseth address extraction, do they not?
I believe hopshots are already past that and the calculation is just about utilization and isomerization.

Yes?No?

Agree on your observation regarding losses in my equipment. I definitely need to account for this.

Thanks again for jumping in.

Bob

Rager, Tinseth and Garetz all address isomerization of the hop alpha acids.  They all model the resultant IBU rest result with one data set of hop %AA input.

The same chemistry applies to the extracted hop oils as with the hop pellets or flowers.  Utilization refers to the efficiency of the isomerization.

This is why the data sheet on the hop shots is a bit confusing.  They seem to jump right past the utilization step to the IBU contribution per ml.  Further, the sheet does not specify if it is an actual test result or based upon one of the models.  This may explain the discrepancy between the 65% AA as listed in beersmith and the 10 IBU/ml from their spec sheet.

Oginme, hope you are willing to stick with me on this. So... What I'm thinking,

Recognizing what you noted about the actual IBU's versus calculated IBU's in the real-world...

I'm going to use your 16.5% calc (based on 1.080) and running it thru for 5.75 gallons, I come up with needing 10.67ml.

I'm going to enter this volume into BeerSmith3 and then adjust the AA number until I get to 80 IBU's, so that at least just as a starting point, the IBU's calcs in BS3 align with my targets.

I'm going to see if I can construct a worksheet that uses Tinseth's, so In the future, I can vary my IBU targets more tightly.

Thoughts?

Making a correlation chart for hotshot in Tinseth is a pretty good idea if you will be using them a lot.  I worry that the target of 80 ibu in Tinseth has a much different perception than 80 ibu in Rager.

If you are going to do this, I would recommend zeroing the other hops and focusing on just the ibu contribution from the hotshot as a start.


edit: spelling

Wanted to follow-up on this thread. I used the Hopshots as noted above. The finished product was very Sweet. So the amount was way off. Will need to rethink this.