IBUs - Let's get this sorted out.

It's certainly why I hang around. I wouldn't know diddly about brewing and a lot of other stuff without people like you to learn from.

 

I think bitterness ratio (BU:GU) is way more helpful. Brewers surely have the info, but probably just don't post it on their cans because it's not as sexy as IBU's (which are usually only posted on hop-forward beers).

 

Right. But the majority of the world will say that a teaspoon of sugar is sweet. That a lemon is sour. That a banana tastes like a banana and not a lobster. To me, this means that the the majority of the population perceives tastes in a similar way.

How would a restaurant operate if everone tasted things as differently as your post indicates? There is enough commonality in tastes for them to exist

 

IBUs denote parts per million of isomerized alpha acids. They are of no use to you unless you make beer. Even if you do make beer the concept is of little use unless you have access to expensive lab equipment and the training to use it. Most small breweries and almost all homebrewers do not. If you don't have these things all you can do is calculate IBUs using one of a range of ludicrously inaccurate formulas which will give you a number that is probably in no way representative of the actual bitterness of you beer (this is how we get numbers like 120IBU, 1000IBU, etc when somewhere around 100 is the actual physical upper limit).

The only people who should be talking about IBUs are people with serious chemistry labs and entry level beer geeks who want to sound like they know what theyre talking about when they absolutely do not.

 

It's exactly how IBU's are measured or calculated which interests me. As a person who is a serious analytical chemist, I'm curious what methodology and equipment is used to measure and quantify IBU's. I'm going to assume this is done chromatographically but I'd like to know a few more specifics.

 

I'm curious why I've heard ibus can't actually be higher than 100. Why not?

 

For further research (all you beer geeks), try

http://homebrewmanual.com/what-are-ibus/

All this talk about IBU's has made me crave an Imperial IPA - cheers!

 

It's claimed that human perception only goes up to about 100, such that we can't taste the difference between 100 and 1000.

 

I'm not a chemist, but my understanding is that it can be measured with a UV spectrophotometer. Not a hugely expensive piece of equipment, but something 95% of craft breweries aren't going to have.

There is some more detail in the last post on this thread: http://discussions.probrewer.com/sh...meter-amp-microscope&highlight=ibu+microscope though you would probably have to join the ASBC (american society of brewing chemists) to get a detailed methodology.

 

Most people can only taste around 80-100, and the solubility limit in wort is something like 90-110, any more that that will just precipitate out.

 

Following that logic I guess we should leave IBUs to chemists only and government to politicians only and drinking beer to beer drinking professionals only.

 

At a recent talk, a brewer said at festivals the following progression happened in questions they would get over the years.

"What is your thickest, darkest beer?"
"What is your highest ABV beer?"
"What beer has the highest IBU level?"

He then laughed.

 

I got the question at bar trivia a couple weeks ago, what does IBU measure?

I wrote "alpha acid concentration/bitterness" knowing the correct answer was "Bitterness", but part of me was tempted to just put the real correct answer so I could explain to the trivia jockey after that my answer was actually correct.

 

I don't know why he laughed. Was it because they were silly questions? Or was it to show how people used to be interested in dark beers, and then high alcohol percentage beers, and now very hoppy beers? If the latter, I fail to see why that is funny (not faulting you hopfenunmaltz, but the brewer who laughed). Would it be funny if someone asks next year what the most sessionable beer is or what barrel aging program they might get involved with?

 

Someone on here had the idea of using a slider (on a "bitterness scale" and others) for reviews. That would be kinda cool.

 

You are pretty close but your not being very nice. The reason it is difficult to estimate IBUs is because the formulas are based on a utilization factor. Theoretically speaking the highest amount of alpha acids that could be utilized (isomerized) is somewhere in the 30-40% range assuming you boiled the hops for 75 plus minutes. However there are many other variables such as the gravity of the beer, the volume of the beer, the brewers system and the quality/variety/age/method of introduction of the hops. The formulas are not inaccurate there are just many variables and varying opinions regarding the utilization continuum. The actual levels can be analyzed in a laboratory by people smarter than me. What compounds this are the modern practices of late kettle hop additions/hop stands/dry hopping etc. and to my knowledge it is relatively unknown how much bitterness these practices actually contribute. I also don't think that you can definitively say that 100 is the physical limit. Some brewers may use their calculations as a marketing ploy, but that is hardly as ridiculous as some of AB/MC's tactics. I'm just a brewer not a scientist so that is my best explanation. Most of us try to use IBU's to give our customers an idea of what they are buying just like gravity, abv and perhaps a list of ingredients. Cheers.

 

He had been talking about his IPA, which is more balanced than most and not really high in IBUs. It is 70% of his production. They make a lot of it.

He was also illustrating how the trends have changed over the years, and he has been brewing for a long time.

 

I'd guess he laughed because all three questions were asking about extremes. Darkest, strongest, most bitter. I can also certainly relate to those that asked the questions- it's the American way "If some is good, more is probably better"

 

I just remove the labels from my beers so I dont get confused by the numbers and letters and I can just enjoy the beer.

 

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!