IBUs - Let's get this sorted out.

God forbid they actually ask which one is the best. Oh well, at least it's easy to play these people like puppets if you really wanted to...

 

Could you have some of your beers tested (at Siebel, or another lab), and then use that information to be a little more precise with your utilization assumptions going forward?

 

Yes, but there will always be some variance based on some of the variables I mentioned. That being said I have moved out of the production brewing world and currently am working in the pub brewing world where I mostly brew one offs. The formulas used to calculate IBUs are generally pretty accurate but in the case of over the top IPAs/DIPAs and such I'm not sure it would be of much use. Also our money is better spent having our beer and yeast analyzed for potential faults, so we can put out the best product possible. As a whole we try to do the best we can to inform our customers. I know the price point of american craft beer is very high and I want people to have an idea what they are getting. I personally really enjoy connecting with the people that drink my beer and that's why I do it. Cheers!

Also I do not work for Cigar City and should probably change my image, I dont post often enough.

 

I would highly recommend this article to @Hop-Droppen-Roll : http://byo.com/stories/article/indices/37-hops/200-behind-the-ibu-advanced-brewing

In the beginning of this article it mentions:

“The definition of IBUs that most homebrewers are familiar with is one IBU equals 1 milligram (mg) of isomerized alpha acid per liter (L). (Equivalently, one IBU can also be expressed as one part per million (ppm) iso-alpha acids.) In practice, however, measured levels of IBUs in a beer may deviate from this definition.”

I bolded the last sentence because in practice IBUs are measured by Spectrophotometric methods. Using a spectrometer you measure the amount of absorbance at a wavelength of 275 nm. Below is the formula and some further explanation:

“The formula is: IBU = 50 x Abs@275nm

where Abs@275nm stands for absorbance of the sample at 275 nm. The number 50 is a coefficient, rounded down from 51.2, based on the slope of the correlation and ratio of solvent used.”

The wavelength of 275 nm was selected since this corresponds to isomerized alpha acids but there are other compounds in beer which can absorb light of a wavelength of 275 nm. One example is hop polyphenols. There are other compounds beyond that one example.

So, while measuring absorbance at 275 nm is an ‘indicator’ of the amount of isomerized alpha acids in a beer it is not 100% precise since there are other compounds beyond isomerized alpha acids that can also absorb at that wavelength.

Other folks have already addressed the topic of perceived bitterness vs. measured bitterness.

Cheers!

 

Thanks, and that does make sense. Best wishes to you and the brewpub.

 

Absolutely, again I want to point out that I am not a scientist and that there are people who know far more about this subject than I ever will. I just think it is important for the average brewer to have some representation on this forum. This forum is a large reason why I work in this industry. Thank you for your wishes and we will continue to do the best we can with in our means.

 

it kind of sucks that IBU doesnt help figure out which beers will taste bitter to the tongue. I have been a fan of getting IBUs as I cant stomach the bitter taste. However looking at the IBU of stouts I love I see IBUs that would make me shudder while a beer I hated because of its bitter after bite I was informed that it was only 30 IBU.
its all very well to say buy just one but when beers can run 10-20 a go that is one expensive drain pour of a neer another BA would die for.
IBU doesnt work but damn it I wish there was some measure that would work. It sucks searching out a beer paying a fortune for it only to be unable to stomach it.

 

Plus, at a fest where you've got a huge line to try your beer, and everybody asks the same three questions all freaking day long, the questions start to get funny to you. I've poured fests where we (the pourers) will start betting on which person line asks which one of the 3-4 same questions.

 

While its not a measure, I find that checking a few of the descriptions by the top reviewers on a site like this before buying something I'm interested in trying can reduce the possibility of my buying something I'll later regret.

 

“IBU doesnt work but damn it I wish there was some measure that would work.”

Permit me to ask: have you ever drank a beer with a low IBU number that tasted too bitter to you?

Cheers!

 

There have been some recent studies that make the whole Cohumulone is bad thing questionable. Hey, I also believed that for years. The one I saw recently is behind a login wall, so I can't link to it.

 

Simple liquid extraction with acidified octane, shake for 15 minutes, centrifuge, and then measure absorbance of the solvent layer at 275 nm. Will measure mainly iso-AA, plus some minor contributions from beta acids and polyphenols. Pretty interesting that a process control measurement has become a selling point for consumers. Waiting for [Ca2+] or FAN levels to show up on a label some day soon.

 

no, that's pretty much it. more detailed explanations really just amount to the same thing. IBU measure bittering compounds, but other factors affect perceived bitterness.

 

Also decomposition products of alpha and beta acids (which are not bitter).

Cheers!

 

I know percieved bitterness has been already been mentioned but here is an interesting tidbit. Beer at the 45-50 IBU level begins to cause salivation. Finished beer is around pH 4 and saliva is around pH 7 effectively making bitter beer seem more bitter.

If folks start worrying about FAN levels and such small breweries might have to throw in the towel.

 

Is this regardless of style?

 

That sir is a good question, I originally wrote very hoppy beers and then decided to try to be more empirical. I should stick to brewing and not talking.

 

This is the best summary in the thread, and if you don't mind, I'll discuss it a little bit more.

The orignal question was: What does IBU actually measure? The answer is very simple: the IBU assay measures everything that absorbs light at 275 nm. EVERYTHING. Many of these molecules have bitter flavors, and some do not.

Here's a short non-exhaustive list of things in beer that get measured by an IBU assay: alpha acids, iso-alpha acids, oxidized alpha acids (humulinones) beta acids, oxidized beta acids (hulupulones), polyphenols (a very large and diverse family which includes tannins), and malt melanoidins.

Now, the kicker is that all of the above things will absorb 275 nm light at varying intensities. 275 nm was chosen specifically because iso-alpha acids absorb very strongly at that wavelength and alpha acids absorb weakly (in comparison). The degree to which iso-alpha acid absorption makes up the majority of the overall absorption depends heavily on the type of beer, which leads me to the next part of the discussion:

The IBU assay was developed in the 1960s, before liquid chromatography had been fully developed. It was also developed in a period where German style and American style lagers completely dominated the market everywhere but the UK. Therefore, the assay was developed using wet chemistry and dry lager beers. In that style of beer, the IBU number correlates with the perceived bitterness with a very high correlation coefficient, because iso-alpha acids represent almost all of the absorption of light at 275nm. A German lager weighing in at 25 IBUs will probably have 23.5-24 of those IBUs resulting from iso-alpha acids (with the remainder coming from polyphenols and malt melanoidins). More specifically, it will probably also have very close to 23.5-24 ppm of iso-alpha acids.

If you instead run an IBU assay on an American Style IPA which comes out at 65 IBUs, it probably has somewhere in the neighborhood of 40-55 ppm iso-alpha acids (a big possible range). A great deal more of the aggregate absorption is coming from other things, especially if it has been dry hopped. Dry hopping acids a ton more polyphenols to the beer, as all as alpha acids (which are not particularly bitter until isomerized) and humulinones (which are bitter, but not as bitter as iso-alpha acids).

In summary, the IBU assay only correlates to mg/L iso-alpha in a few specific beer styles, and still not at a 1:1 basis in those. Lots of things contribute to bitter flavor, which may or may not be measured by the IBU assay.

All of this is to say the IBU assay is an okay method to use in a beer lab for maintaining process consistency, but is verging on uselessness when it comes to communicating flavor profile to a beer drinker. I suspect brewers add it to the label because people ask to see it, not because they think it's a particularly good way to describe their beer. I hope that helps!

 

@Peter_Wolfe , thank you for your contribution above!

Cheers!

Jack

 

This last part makes it seem like you're saying that the IBU number that brewers add to their labels is usually the result of this IBU assay you describe, when in fact I believe it's usually just a number calculated from the recipe that may or may not be even close. I think it is worth considering if this "calculated IBU's" number gives a better or worse indication of how the perception of bitterness will be. From your description of the IBU assay, it seems like it could hardly be worse....

Absolutely it helps, thanks!