Calculating IBUs

This might be a dumb question but why do different IBU calculators on the Internet give different values? Does anyone know a website that gives the most accurate calculation?

If I'd have to guess why they calculate differently, I'd say each program might use a slightly different Alpha Acid value for each individual hop. Completely possible depending on where and what year they're pulling input data from. Hop values can fluctuate up and down slightly each season.

Yea but even when I plug in the AA values they give me different IBUs. It's weird

bsyoung said:

This might be a dumb question but why do different IBU calculators on the Internet give different values? Does anyone know a website that gives the most accurate calculation?

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No, but if you find one let me know!

There are many reasons why they differ- some use different formulas (Rager, Tinseth), and some use different ways to figure the calculation. Some use wort gravity, some use boil size, some use only standard AAUs, etc.

The best advice I can give is to find one that seems to work for you, and stick with that one. I mean, 50 IBUs Tinseth in my system may taste remarkably like your 35 IBUs Rager in your system. But if it seems "right" to you, then use that scale for all of your batches to adjust, and forget others IBU ratings for different systems.

Also, look at the IBU/Sg ratio for a better idea of "bitterness" as a beer of an OG of 1.038 and 25 IBUs will be pretty bitter, but a beer with an OG of 1.080 and bittering of 25 IBUs will be underbittered and be sweet.

Yooper said:

No, but if you find one let me know!

There are many reasons why they differ- some use different formulas (Rager, Tinseth), and some use different ways to figure the calculation. Some use wort gravity, some use boil size, some use only standard AAUs, etc.

The best advice I can give is to find one that seems to work for you, and stick with that one. I mean, 50 IBUs Tinseth in my system may taste remarkably like your 35 IBUs Rager in your system. But if it seems "right" to you, then use that scale for all of your batches to adjust, and forget others IBU ratings for different systems.

Also, look at the IBU/Sg ratio for a better idea of "bitterness" as a beer of an OG of 1.038 and 25 IBUs will be pretty bitter, but a beer with an OG of 1.080 and bittering of 25 IBUs will be underbittered and be sweet.

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That makes since. Do you know which method commercial brews use (Rager, Tinseth, etc)?

bsyoung said:

That makes since. Do you know which method commercial brews use (Rager, Tinseth, etc)?

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Yes, those. And others.

But, most of the bigger ones use testing with spectrometers to measure the actual, not calculated, IBUs.

Calculating them is an iffy business. Even if you could calculate accurately, there are limits to the amount of hops oils that can isomerize in wort (usually agreed to be 100 or so) so even the hoppiest beers you can think of that calculate in theory to 200+ IBUs, don't. Even Pliny the Elder, probably one of the most famous DIPAs has an actual IBU measurement of something in the 80s, I believe.

Thanks Yooper