[Dave King]

I just lead a "Learn to Homebrew Day" brew, using a Brewers Best Kit for an American Pale Ale, simple, right?

Well, the bitter wort tasted rather extremely bitter for that style, and the directions say O.G. = 1.051 to 1.055, 32 to 36 IBU, which seems lightly bitter, so I put the orginal gravity and hopping schedule into my spread sheet, which uses the Pyle's Hops FAQ, 5/4/95 Rager formulas.   See;

     http://realbeer.com/hops/FAQ.html

With O.G. = 1.054, 2 oz. of 6.9% AA Cascade at 60 min., and 1 oz. of 12.5% AA Citra at 5 min. left, I get 80 IBU.  Hmm, about what it tastes like, a very bitter IPA, although before fermentation it's hard to tell much by taste.

So I went to http://www.brewersfriend.com/ibu-calculator/ and it says 60 IBU, using Tinseth's equations. 
 
Beersmith says 105 IBU. 
 
Brew 365, http://www.brew365.com/ibu_calculator.php says 60 by Tinseth, 57 by Rager.
 
Tasty Brew, http://www.tastybrew.com/calculators/bitterness.html says 57 IBU by Tinseth.
 
My old Rager calculation from Pyle's Hops FAQ, 5/4/95 is what I’ve been using for nearly 20 years, and it’s 80 IBU is in the middle, but what a range!  Amazing.  I know IBU calculation is rough, and not very accurate, but the results here are all over the map.  I'd expect the Rager from all sources should be within a couple points at most.  Any idea what's up here?  I think I entered the date correctly in all cases.  Thanks!
 
    Dave

[kramerog]

If you do a full boil you should get a bitterer beer because the kits are generally designed for partial boils.  Of course the kits don't specify the amount of water to use. 

Beersmith uses Tinseth so I think that you may misentered something somewhere. http://www.beersmith.com/Help/estimating_bitterness_tech.htm

[HoosierBrew]

I don't know Dave - I get from 66.75 IBU in Brewer's Friend for 5 gallons @ 1.054, with 56.5 IBU from the Cascade, 10.25 IBU from the Citra  (given boiling 6.5 gallons down to 5 gallons in 60 mins). Is it a 5 gallon batch ? As BJCP lists APA @ 30 -45 IBU, I normally add 35 IBUish @ 60 minutes, picking up the balance to get near 45 as late boil - I like the hoppier end of the APA spectrum. Or more accurately , lately I've been doing a 60 mins addition, adding 40 IBU for 60 mins, then the late hops post boil as 165-170F whirlpool/hop stand hops. Nonetheless, I wonder about your volumes.


EDIT  -  BTW that was Tinseth. If it is a 5 gallon batch, 56 IBU as a bittering addition (60 mins) is definitely IPA territory.

[dmtaylor]

I calculate approximately 60 IBUs via Tinseth.  The Rager formula is way goofy and not nearly as accurate.  No formula is perfect, but Tinseth comes closest.

[Dave King]

We were a little shy on the volume, mixed approx. calibrated equipment, and a big immersion cooler, I was not familiar with.  I think we had about 5 gal. bittered, and yielded about 4.5 in the fermenter.

We did a full boil, and indeed, diluting a more concentrated wort boil would yield somewhat less IBU.  That's not my big concern now.  I'm concerned at the great range in IBU I got from the differennt calculation sources.  Maybe I should go to Tinseth, but it should be a relative measure, which is how I've always treated it. 

The Rager 60 vs. 80 is botheriing me, and I rechecked my inputs for BeerSmith, there was a small pot selected, so I selected a larger one, and got 83 instead of 105 IBU, which makes no sense to me, but it does get closer to my 80 IBU from Pyle's equations. 

Anyone know of a good source for the Tinseth formulas?  Thanks,
 

[hopfenundmalz]

"Anyone know of a good source for the Tinseth formulas?  Thanks,"

Yes I do. Your welcome Dave.

http://realbeer.com/hops/FAQ.html#units

[dmtaylor]

The following is a very close estimation method that very closely emulates the results you would get from Tinseth.  I like to call this “the Taylor formula”.  Give it a try and see how close you get to Tinseth.  These rules are designed for pellet hops used in 5 gallons final boil volume, 60-minute boil, @ approximately 1.060 OG.

3.6 * oz * AA% = IBUs from bittering hops added @ about 60 minutes left in the boil
1.6 * oz * AA% = IBUs from flavor additions @ 10-15 minutes
0.6 * oz * AA% = IBUs from aroma @ 5 minutes

Add all these together, and then add another +1.5 to the final total to get the final grand total IBUs.

For higher gravity worts (e.g., >1.075), the primary factors are reduced somewhat to about 3.0, 1.3, and 0.6 (stays same).  For low gravity worts (e.g., <1.045), the factors are increased to around 4.0, 1.9, and 0.6 (this third factor always stays same). 

For different batch volumes (V) other than 5 gallons, you need to multiply the result by 5/V.  If you use whole hop cones, then multiply your final result by 0.9 (a.k.a., 90%).