Bitterness Determination - The Great IBU Debate
Bitter Beer Face in Five Easy Lessons

When I started brewing, I was content to use the estimation method that I found in the hops issue of Zymurgy magazine. It is similar to (if not identical to) the method that Dan McConnell uses: a linear utilization of 30% for full 60 min boils and 15% for 30 min etc, essentially the number of minutes of boil divided by 2. I modified this slightly when necessary, such as in high gravity boils.

Then I found Randy Mosher's book. The charts of hop utilization may not be TRUTH, but they look a lot like it! There was the fudge factor for high gravity worts, and the increasing utilization based on time of boil. I clasped this chart to my bosom, and plodded on. I figured out extremely complicated 7th order curve fits to match several of the curves, and incorporated these equations into a spreadsheet that I use to figure my recipies.


IF((time)>=60,(-75242.3438*(grav)^4 +319260.6250*(grav)^3 -507038.7800*(grav)^2 +357282.030*(grav) -94261.6480),
IF((time)>=45,(-57074.3984*(grav)^4 +242403.3910*(grav)^3 -385243.2800*(grav)^2 +271586.500*(grav) -71672.3120),
IF((time)>=30,(-33593.0508*(grav)^4 +144823.8130*(grav)^3 -233397.8900*(grav)^2 +166711.070*(grav) -44544.0310),
IF((time)>=15,(-11225.9502*(grav)^4  +48676.1289*(grav)^3  -78680.5150*(grav)^2  +56236.753*(grav) -15006.4370),
IF((time)>=5, ( -4327.4790*(grav)^4  +17081.0352*(grav)^3  -24950.7168*(grav)^2  +15961.039*(grav)  -3763.8664),

It was this process that was challenged by George Fix's experiments in IBU determination. He reported two recipes whose IBU levels had been measured by top government scientists, on loan from the FBI (Mulder and Scully?). His recipes follow:

George's section ON:

Pilsner: Final volume is 6 gallons.  Original gravity 1.050
    0.75 oz Saaz (AA 3.6%) 75 minutes
    0.50 oz Saaz (AA 3.6%) 60 min.
    1.00 oz Saaz (AA 3.6%) 45 min.
    0.50 oz Saaz (AA 3.6%) 15 min.

Reported IBUs: 25.6
Rager's calculations gave me 32.75 IBU.
Garetz's calculations gave me 26.47 IBU. Garetz was close enough for a match.

California Common: Final volume is 6 gallons.  Original gravity 1.050
        .92 oz Northern Brewer (AA 8.2%) 70 minutes
        .49 oz Cascade (AA 5.7%) 25 minutes
        .46 oz Northern Brewer (AA 8.2%) 10 minutes
        .46 oz Northern Brewer (AA 8.2%) 2 minutes
        Finishing hops were added at the end of the boil but should be of no
consequence to the IBUs.

Reported IBUs: 35.3
Rager's calculations gave me 35.8 IBU
Garetz's calculations  gave me 22.6 IBU. Rager was close enough for a match!!

George's section OFF:

I can't argue with that. The man made some beer, and sent it off to the lab. You could argue with the numbers, but I won't. This is a data point.

I used my ever so mathmatically impressive spreadsheet to determine what numbers I would have come up with based on these recipies. Guess what? They come out different!

Pilsner:    18.9 IBU total
    0.75 oz gave 6.4 IBU
    0.50 oz gave 3.9 IBU
    1.00 oz gave 6.7 IBU
    0.50 oz gave 1.9 IBU

Common:     25.0 IBU total
    0.92 oz gave 17.3 IBU
    0.49 oz gave 4.0 IBU
    0.46 oz gave 2.9 IBU
    0.46 oz gave 0.8 IBU

What does this tell us? It tells us that we are GUESSING as to what leads to hop utilization and bitterness. We know what makes it go up and down, but we are clueless as to the 'real' numbers.

So how 'bout this. Find a method for determining IBUs. Stick with it. Test it. Explore it. Change it if you feel like it, but be consistant. If your pale ales aren't taking you to hop heaven, change your method. If your bocks are a little too bitter, change your method. I'm not going to say that Randy Mosher is God, but he's got a chart that can be used as a starting point. I've got a couple of excuses for why none of these things agree. But as a brewer, it's as much art and experience as science. My spreadsheet is just a tool, and I use it for tuning up my recipes.

For a more intensive discussion of the different methods of determining hop bitterness, I refer you to Norm Pyle's Hops FAQ and other stuff found off of The Real Beer Page.

Have fun...

Copyright 1997 by Rich Webb, aka The Outsider.

This page is authored and maintained by Rich Webb (aka the Outsider). You can send E-mail to him at Feel free to contact me if you have any comments, criticisms, or suggestions..

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What 4-6 hops do you have in your inventory for ale brewing?

                                % of
Hop Variety             Votes   occur.  Bitter  Finish
E. Kent Goldings (EKG)  14      78%     2       7
Cascade                 13      72%     1       7
Northern Brewer         10      56%     4       1
Saaz                    10      56%             3
Perle                   7       39%     1       1
Fuggles                 6       33%     1       1
Hallertauer             6       33%     1       1
Centennial              4       22%
Chinook                 4       22%     3
Columbus                4       22%     2
Mt. Hood                4       22%     1       2
Galena                  3       17%     1
Liberty                 3       17%     1       1
Styrian Goldings        3       17%             1
Tettnang                3       17%     1
Challenger              2       11%     1       1
Willamette              2       11%     1
Brewer's Gold           1       6%
Eroica                  1       6%      1
Northdown               1       6%
Oregon Goldings         1       6%
Spalt                   1       6%
Total reponses          18
Total votes             103
Average value           4.682

Clearly, EKG, Cascade and Saaz dominate as the preferred aroma/flavour hops.
Northern Brewer is the most popular bittering hop with Perle not far behind.
Statistically speaking, the sample set for this survey was pretty small so the
results are not particularly precise.  But, roughly, given a hop selection of
4 varieties, HBDers are most likely to have EKG, Cascade, Northern Brewer and
Saaz in their freezers.  Also common are Perle, Fuggles and Hallertauer.

Most common bittering hops:     1.  Nothern Brewer
                                2.  Perle

Most common finishing hops:     1.  EKG
                                2.  Cascade
                                3.  Saaz

other notes:

- unless otherwise noted, 'Goldings' was taken to mean EKG
- the bitter/finish incidences were only recorded if the voter specifically
said he/she used those hops for that purpose
- voters didn't differentiate flavour from aroma use
- the original German strains were often specified in the case of Hallertauer
and Northern Brewer;
- if you combine the Mt. Hood and Liberty votes (both bred as US versions of
Hallertauer) you raise their total to 7 - 4th highest finish hop
- several brewers said they preferred to avoid high-alpha hops, but Chinook and
Columbus (both >10% AA) were quite popular overall
- higher alpha varieties were said to produce a more intense, sharp bitterness,
while lower alpha hops produced a softer, rounded bitterness (for the same IBU
- imported varieties were at least (if not more) popular than domestic ones
suggesting the HBDers are not concerned with price relative to stylistic
accuracy; it may also imply that decent quality imported hops are available to
most HBDers
- the survey request was designed for Ales, some responses did not specify
only for that category, hence numbers for Saaz and the German noble hops may
not correctly represent their usage

* I'm not a statistician so don't torch me into a smoldering lump of goo if
I've made some gross generalization or horrendous error.

Dave Riedel 
Victoria, BC


This page is authored and maintained by Rich Webb.You can send E-mail to me by following this link to the contact page. And feel free to contact me if you have any comments, criticisms, or suggestions. I remain, however, perfectly capable of ignoring your useless opinion...

This document was placed here on May 13, 1997, and has been viewed countless times.