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Old 06-25-2010, 02:20 PM   #1
Apr 2009
North Mississippi, USA
Posts: 66

Ok, I'm trying to figure out what the gravity and IBU's are on this recipe and have used beercalculus, tastybrew, and brewpal (iphone) to try and estimate what my results should be. All three came up with wildly different results and I don't understand why.

Recipe - Rye Pale Partial Mash
-- 3 lbs Rahr 2-row
-- 1.5 lbs Weyermann Rye Malt
-- 0.5 lbs Carared
-- 6 lbs Amber malt syrup late addition (15 min)
-- 1 oz Summit 18AA (60 min) pellet
-- 1 oz Palisade 7.5AA (15 min) pellet
-- 0.5 oz Palisade 7.5AA (5 min) pellet
-- 0.5 oz Palisade 7.5AA (dry hop) pellet

OG: 1071
IBU: 46.8 ??
ABV: 6.9%

OG: 1069
IBU: 97 ???
ABV: 6.7%

OG: 1067
IBU: 66 ??
ABV: 6.8%

Ok, I can live with the gravity being pretty close, but what is going on with the IBU's? I tripled checked to make sure I put in the numbers the same on each one but the results always came out this differently. What gives?


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Old 06-25-2010, 02:42 PM   #2
Dec 2008
Posts: 184
Liked 11 Times on 7 Posts

I use brewpal and beertools and have also noticed in the past that they can sometimes come up with different measurements that I can't explain. That having been said the bitterness shouldn't be so wildly off. Here's what you want to look for:

There are different bitterness algorithms that can be used by these programs and you generally want to make sure that pick one and stick with it. I know brewpal let's you choose between the tinseth and rager formulas in the settings menu on the hops page.

You should also check to make sure that each program is making the same assumptions about factors like boiloff rate when it comes to gravity.

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Old 06-25-2010, 02:50 PM   #3
smakudwn's Avatar
Mar 2009
St.Charles, MO
Posts: 1,046
Liked 59 Times on 43 Posts

3 different methods to calculating IBU.


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Old 06-25-2010, 02:53 PM   #4
Feb 2010
Gainesville, Fl
Posts: 639
Liked 6 Times on 6 Posts

I got 1.072 and 70.1 IBUs using ProMash @ 75%. Tinseth formula with a correction factor of 1.0

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Old 06-25-2010, 02:55 PM   #5
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IrregularPulse's Avatar
Nov 2007
Posts: 52,084
Liked 3594 Times on 3395 Posts

As some one told you in the other thread you started with the exact same topic. Different IBU rating scales. Tinseth, Rager, and Garetz (sp?)
Tap Room Hobo

I should have stuck to four fingers in Vegas.

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Old 06-25-2010, 06:10 PM   #6
Feb 2009
Alexandria, VA, USA
Posts: 2,057
Liked 32 Times on 28 Posts

IBU estimation is a black art. As noted, there are many different formulas for doing it that can vary wildly in their predictions--Tinseth, Rager, Mosher, Daniels, and Garetz are the most common, though there are others. Basic Brewing Radio did a show on this--they used several different formulas to guess, then actually had the real IBUs measured in a lab.

One recipe varied from 18 IBUs to 74 IBUs as estimates (actual: 34).
In some cases, the spread of the formulas didn't even contain the actual answer--e.g. a hefeweizen where estimates ranged from 12 IBUs to 17, but actually measured just 7 IBUs.

My personal takeaway was:
1. Pick one formula and use it the same way consistently; that way you'll have a consistent baseline that you'll learn how it comes out flavor-wise (I chose Tinseth, as it seemed most accurate to me); and
2. Only expect accuracy to about +/-30% in the estimates*. If the prediction is 50 IBUs, you can be reasonably confident that it's in the 35-65 IBU range, but don't expect it to be spot-on.

*Or even worse for unusual beers (e.g. anything with wheat/rye, partial boils, unusual hopping schedules, crazy yeast, etc)
On deck: Little Bo Pils, Bretta Off Dead (Brett pale)
Secondary: Oude Bruin, Red Sky at Morning (Sour brown ale)
On tap: Saison Duphunk (sour), Amarillo Slim (IPA), Earl White (ginger/bergamot wit)
Bottled: Number 8 (Belgian Strong Dark Ale), Eternale (Barleywine), Ancho Villa (Ancho/pasilla/chocolate/cinnamon RIS), Oak smoked porter (1/2 maple bourbon oaked, 1/2 apple brandy oaked)

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