Tastybrew IBU Calculator?

I was wondering how accurate the Tastybrew IBU calculations are (from their recipe calculator). I just made this recipe, and I don't quite believe the predicted IBU of 50:

Best Bitter
Batch size: 4.5 gallons
Boil size: 3 gallons

6 lbs LME
1 lb English 2 row, steeped
1/2 lb Carahell, steeped

0.75 oz Northern Brewer hops, pellets, 10.1% AA, 60 minutes
0.5 oz Fuggles, pellets, 4.0% AA, 15 minutes
0.5 oz Fuggles, pellets, 4.0% AA, 1 minute

If I change the "Boil size" to 4.5 gallons, the predicted IBU drops to 37. It was my understanding that the more sugar in the wort, the lower the hop utilization, which is counterintuitive with the Tastybrew results. I know my way of thinking is probably wrong some where. It's also possible 50 IBUs just don't taste nearly as bitter as I thought, but this beer feels to me significantly less bitter than a commercial Roxy Rolles, which clocks in around 40 IBU according to the Magic Hat site.

I come up with 33.5 IBU for that hop schedule. I'm not sure the effect a smaller batch/boil has on my formula since I use pen and paper not software. You can try one of the free trial programs like Beertools or Promash to double check your results.

Had this conversation with someone yesterday. I think it's really inaccurate. Plugged my recipe into the hopville, tastybrew, beersmith, and one other commercial calculator.

The two commercial calculators came up with IBUs that were similar to eachother (around 50). The tastybrew and hopville calculators came up with wildly different IBUs. Hopville came up in the low to mid thirties. Tastybrew came up in the low 40s. If I decreased the boil size from 5 gallons to 4 gallons (but kept a 5 gallon batch size), the hopville, beersmith, and other commercial calculator brought the IBU down a couple points, while tastybrew jumped 20 points.

Thanks, that's good info.

Clonefarmer said:

I come up with 33.5 IBU for that hop schedule. I'm not sure the effect a smaller batch/boil has on my formula since I use pen and paper not software. You can try one of the free trial programs like Beertools or Promash to double check your results.

Click to expand...

Which formula are you using? 33 is around what I would guess from tasting of this beer, but I am no certified judge.

I just tried Beer Tools (free online), and it gave me 39 IBU, which still feels high (it was very close with the OG, predicting 1.054 instead of my observed 1.052). I also just tried the Tastybrew Bitterness Calculator (not the full recipe calculator), and with a given OG of 1.052 it predicted 25.8 IBU.

oz of hops x AA% x utilization% divided by 7.25 =

Ex. 1 oz AA 10% hops at 60 = 1 x 10 x 30 divided by 7.25 = 41.3
Ex. .5 oz AA 10% hops at 60 = .5 x 10 x 30 divided by 7.25 = 20.6

Utilization chart
minutes boil.......percent utilized
5......................5
6-10..................6
11-15................8
16-20................10.1
21-25................12.1
26-30................15.3
31-35................18.8
36-40................22.8
41-45................26.9
46-50................28.1
51-60................30

Thanks, so you're using the Rager formula. I was just poking around this morning trying to find the data points after 45 minutes, that's great.

phasedweasel said:

Thanks, so you're using the Rager formula. I was just poking around this morning trying to find the data points after 45 minutes, that's great.

Click to expand...

Ah, I didn't know the name of the formula. It came from an old homebrew book I had.

This is one where Tinseth and Rager disagree quite a bit. I used recipator.com and got 28 with Tinseth and 41 with Rager.

I was reading this page
http://realbeer.com/hops/FAQ.html#units
and found this to be interesting:
"The equations are commonly quoted from Jackie Rager's article in the "Zymurgy" Hops and Beer Special Edition published in 1990. Revised numbers and formulae have recently been presented by Glenn Tinseth and Mark Garetz, in separate works. Rager has been taken to task for not supplying enough background references, and not fully explaining how he got his numbers. In general, his utilization estimates are believed to be optimistic. Garetz has been accused of extrapolating scant laboratory information, and overgeneralizing because of it. His numbers have been labelled unrealistic on the pessimistic side. Tinseth has just presented a revised method and set of tables, and though they are thought to be quite accurate, they have not stood the test of time. The calculated numbers tend to fall in between Rager's and Garetz's."

So you're probably pretty damn close when you say you taste 33. I'm impressed.