IBU Discrepancy Between Recipe & Software

[stylus1274]

I bought an IPA kit and the recipe says the IBUs should be 65. I ran the recipe through BeerSmith and it is telling me 43. That's a vast difference. Curious if this happens to others and how to properly handle it. I really would like 60+ IBUs for my IPA

 

[VikeMan]

What's the actual Alpha Acid percentage(s) for the hops you received?
Did you adjust in BeerSmith for the actual Alpha Acid percent(s) if different than the default(s)?
Did you enter the hop timings in BeerSmith exactly the same as the recipe, including any hopstand/whirlpool additions?

ETA: If none of the above helps, maybe post the recipe (or recipe link), and I'll run it through BrewCipher for comparison.

 

[stylus1274]

Nevermind. I believe I figured it out.

If I add a portion of the extract at flameout, the IBUs become very close. I think this is the issue even though the recipe doesn't say add at the end.

 

[marc1]

IBUs are also calculated with a really rough estimation. There are several formulas that can be used, and none are going to be great for all beers. Pick a formula (seems like you've got the default Beersmith one, not sure what it is) and then you'll get used to how bitter the beer you make with your process tastes with different IBU levels under that formula.

 

[dmtaylor]

Following is my own quick & dirty equation. It should come within 10 IBUs compared with any software that uses Tinseth. It's an approximation of Tinseth. The big bonus is that unlike some softwares, it also takes whirlpool a.k.a. hop stand additions into account accurately (at least as far as I can tell).

IBU = oz * AA% * [sqrt(5*Boiltime)/V + sqrt(2*HStime)/V]

where V is volume in gallons, and Boiltime and HStime (Hop Stand time) need to be entered in minutes of course.

Calculate each addition separately and then add them all together. Reasonably easy on a calculator or spreadsheet. For a different method and other rabbit hole ideas, you can click this, I apologize for the mess but it is what it is, somebody might like it, if they're sick or something:

https://live.staticflickr.com/7891/45991029004_df99d89bc1_o.png

 

[RufusBrewer]

While IBU is an absolute unit of measure. The calculation of IBU has no universal formula. While the most popular formula is Tinseth, Tinsth is not the only IBU calculation available.

Even Glen Tinseth has said unless you are using the exact equipment he used to develop his formulas, you cannot expect to get the same results he did.

BeerSmith has a setting where you decide which IBU calculator you want to use. Change them for a given recipe and notice how wide of a range they calculate. How do you know which formula was used in the recipe kit? Was it IBU in Tinseth? Is you BeerSmith set to use Tinseth?