Is there a limit to the IBUs you can get in wort?

This question came up in a different thread, and I thought I'd post the question in it's own thread to see what other's know.

When boiling wort, is there a physical limit to the amount of IBUs you can disolve in it?

I have seen several places that 100 IBUs is the flavor threshold, but there is a question as to whether this is the threshold of the amount that can be disolved in wort.

This difference becomes critical when someone is trying to brew a high IBU beer with a partial boil. If 100 IBUs is the limit, then doing a half boil, the best you can make is a 50 IBU beer. If doing a 1 gallon boil, your limit is now 20 IBUs.

Wikipedia claims 100 IBUs is the limit of dissolved IBUs, but I don't necessarily believe everything written in Wiki. I've also found this limit noted in other places, but they seem to reference Wiki, or use the same wording, indicating they just took Wiki for being correct. I also found it noted in a BYO write-up, which might give it some credibility.

BeerSmith doesn't place a limit on their calculators. BJCP guidelines have up to 120 IBUs in Barleywines and IPAs.

I've read a paper by AJ Delange that states that the wort is saturated with hops oils at 100 IBUs-ish. I can't find it at the moment, but maybe he can give his input into this thread.

(This thread is better in "Brewing Science", I think!)

It's pretty fairly understood that the maximum IBU's that can go into solution is in the area of 100-120 IBU's (or at least that this is all you can taste). I tend to agree with this after making a 250 theoretical IBU Pliny the Elder clone. There's no way it's much over 100 IBU's in perceived bitterness.

sudsmcgee said:

It's pretty fairly understood that the maximum IBU's that can go into solution is in the area of 100-120 IBU's (or at least that this is all you can taste). I tend to agree with this after making a 250 theoretical IBU Pliny the Elder clone. There's no way it's much over 100 IBU's in perceived bitterness.

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The question is whether you can dissolve more than about 100 IBUs into solution, not whether you can taste them. If you only partial boil it will limit the maximum bitterness you can get in a beer to fairly low.

Calder said:

The question is whether you can dissolve more than about 100 IBUs into solution, not whether you can taste them. If you only partial boil it will limit the maximum bitterness you can get in a beer to fairly low.

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Yes, that IS my understanding. I have read several papers to that effect, but I'm unable to put my finger on them at the moment.

Yooper said:

Yes, that IS my understanding. I have read several papers to that effect, but I'm unable to put my finger on them at the moment.

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For something that severely limits many people from properly making some of the heavier beers, I'm surprised there is not much information on it. As I noted in my initial post, there are style guidelines that have bitterness levels up to 120 IBUs.

In the end, your tastebuds will determine how bitter it is. But if you're diluting the wort I can see why you'd care.

sudsmcgee said:

In the end, your tastebuds will determine how bitter it is. But if you're diluting the wort I can see why you'd care.

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Well, I don't dilute- but I still care! When we talk about IBUs, I think it's really important to know the science behind the tastebuds! If the max amount of oils that can isomerize before the wort is saturated is 100 IBUs, then that's an important fact to know in your brewing career.

While there is a theoretical perceived IBU limit, the flavors that large amounts hops add can add and change the flavor.

As a huge hophead, I have experimented heavily with hops. The IBU's do not necessarily speak to the hop flavor. What I mean is that if you choose the right combination and quantity of hops, the flavor component of hops can be literally overwhelming (yes, even to me!).

Even though the IBU's can be greater or less than 120, the perception of hop pungency and flavor need to be separated from the perception of bitterness.

Not sure that made sense...

r2eng said:

While there is a theoretical perceived IBU limit, the flavors that large amounts hops add can add and change the flavor.

As a huge hophead, I have experimented heavily with hops. The IBU's do not necessarily speak to the hop flavor. What I mean is that if you choose the right combination and quantity of hops, the flavor component of hops can be literally overwhelming (yes, even to me!).

Even though the IBU's can be greater or less than 120, the perception of hop pungency and flavor need to be separated from the perception of bitterness.

Not sure that made sense...

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No, it made perfect sense! And I agree. Pliny at 300 IBUs (or whatever the calculated theoretical amount is) doesn't taste like the 100 IBU IPA I made. It's about the same as far as bitterness, probably, but certainly the "extra" hops aren't a waste but provide flavor.

But what precipitated this thread is a conversation about the max amount of hops oils that can isomerized in wort. My understanding is that it's 100 IBUs-ish, give or take. I'm sure I "know" this from some scientific papers and reading, but I'll be darned if I can find those references right now.

Now, the flavor is NOT what I mean and it's really just in theory we're discussing it. But, what happened to start this conversation is this- a guy boils 2.5 gallons of wort and makes 5 gallons batches. That's absolutely fine, of course. But say it's a HUGE IIPA with 90 IBUs. My understanding is that this is just not possible because if any wort is saturated with hops oils so that they can no longer isomerize at 100 IBUs or so, diluting the wort with 50% water at the end of the boil means a 50 IBU batch, no matter what the recipe or the hop additions. It would be a rare occasion when this came into play, but the thought does occur.

Does that make sense? That's what we were discussing (off-topic) in another thread.

Oh, I agree. I missed the other thread... too little sleep!

r2eng said:

Oh, I agree. I missed the other thread... too little sleep!

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Oh, it wasn't really much to miss! It was just a discussion that is better off OUT of where it was, so Calder started a new thread (if I make speak for Calder).

The thing is, I KNOW I've accepted this as science over the years, but I can't remember why/how/who. It'd be nice to see some data and studies on WHY people like me have accepted this!

I'll see if I can find it. I remember reading 2 articles: one saying 100 is the limit, one saying 120.

after some sleep, of course!

r2eng said:

I'll see if I can find it. I remember reading 2 articles: one saying 100 is the limit, one saying 120.

after some sleep, of course!

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Sleep is good!

I know darn well I've read more than two, but some of them were probably older. I think one was by AJ Delange (hopefully he'll pop in here and correct every thing I saw that's wrong) and another by perhaps George Fix? I don't think it was anything by Palmer or I'd probably remember that.

Yooper said:

But, what happened to start this conversation is this- a guy boils 2.5 gallons of wort and makes 5 gallons batches. That's absolutely fine, of course. But say it's a HUGE IIPA with 90 IBUs. My understanding is that this is just not possible because if any wort is saturated with hops oils so that they can no longer isomerize at 100 IBUs or so, diluting the wort with 50% water at the end of the boil means a 50 IBU batch, no matter what the recipe or the hop additions. It would be a rare occasion when this came into play, but the thought does occur.

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More often than you might think. I do partial mash/partial boil, and have done a few bigger beers. They seemed to come out OK. I did an AB clone (boil was 4 gallons for 6.5 gallon batch), target was 85 IBUs. I did a side-by-side comparison, and could not tell the difference. The original was a little bit more rounder/cleaner in it's taste, but there certainly was not a noticeable difference in bitterness.

I have the ability to do a full boil, but it is easier for me (got the process down) to do a partial boil. If I am truly unable to get the IBUs for a big beer, I may have to change to full boil as normal practice.

Yooper said:

Oh, it wasn't really much to miss! It was just a discussion that is better off OUT of where it was, so Calder started a new thread (if I make speak for Calder).

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Rather than being a secondary discussion in another thread, I thought it might get more attention being the main subject.

Like everyone's said, most of what is talked about is the percieved Ibu in a beer, not what's being asked here.

I haven't listened to this in years, but I vaguely remember Palmer talking about the idea or percieved IBU and iirc how many alpha acids can actually be held in wort.

It may be worth taking a listen to see.

Basic Brewing March 20 said:

- What Is an IBU . . . Really?
John Palmer, author of How to Brew, shares information from a conference that challenged his concept of what defines an International Bitterness Unit (IBU).

click to listen.

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This was right when Palmer had got back from a conference that totally blew his mind and where he backpedalled on his explanation in HTB. I swear be did cover what you are asking Calder.

What happens if I am boiling wort and I've already reached this limit of 100-120 IBUs (or whatever limit you think there is), and I continue to boil? What if I had 5 gallons when I hit the limit and I boiled down to 4 gallons of wort?

What happened to all of those isomerized alpha acids? Were they boiled off? Did they precipitate out?

Oh my, there is a lot of crap mentioned in this thread. Its nice that Pliney is mentioned here since Vinnie provides direct confirmation of what I'll tell you here.

Vinnie says that Pliney calculates at an IBU level of way north of 100 (I don't recall what the exact number was) and he has had lab testing performed on many of the beers off the line over the years. He said the typical result was around 75 ppm iso-alpha acids and it may approach 80 ppm.

That result directly from Russian River correlates well with the results that Malowicki and Shellhammer found for alpha acid saturation level in wort. They found the maximum solubility was 80 ppm alpha acid. There is a limit to the conversion of alpha acids to iso-alpha acids of about 90%, so maybe that number that Vinnie mentioned is reasonable.

By the way, in another Thesis by one of Shellhammer's students, the solubility measured for alpha acid solubility in beer is quite low. It was like 10% and we should remember that alpha acids provide little bitterness perception. That paper said that dry hopping adds very little bittering to a finished beer.

So, the comments of 100 to 120 IBUs in beer are pure crap. It has not happened yet and the science says it can't happen.

LVBen said:

What happens if I am boiling wort and I've already reached this limit of 100-120 IBUs (or whatever limit you think there is), and I continue to boil? What if I had 5 gallons when I hit the limit and I boiled down to 4 gallons of wort?

What happened to all of those isomerized alpha acids? Were they boiled off? Did they precipitate out?

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link
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On IBUs... Deschutes' seasonal beer Hop Henge used to advertise 95 IBUs on the label. They posted a blog article about it (though it doesn't exist on their site anymore) a couple years ago that eventually decided to get it tested and it showed up as 80. The next year they made it they decided to bump it up with a substantially greater amount of hops and only got 87.

They wrote the following:
"The moral of the story for us is we will not again put 95 IBUs on the label. The moral of the story for you might be a wink next time someone tells you their beer has 120 IBUs in it (or even 95 for that matter)."

SPLASTiK said:

link
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Thanks!

Every published formula I have seen for estimating IBUs has more than an outside chance of giving you a grossly inaccurate estimate of the bitterness in your finished beer. That's why I use HBUs.

James Spencer had a podcast not too long ago with some scientist, where they experimented to try and determine maximum IBU content. The maximum they were able to measure, in a very simple beer, was ~60IBUs. Not sure whether that result would hold up across a broader experiment (they were only doing a single-hop addition, as I recall, and I think a 1.040-ish wort), but the important takeaway was that there was a sharply reduced amount of extra IBUs being added once you got around 50IBUs; add 50% more hops, you might only go from 52IBUs to 55IBUs, something like that. They did not change the wort gravity - be interesting to see the effect of X amount of hops in a 1.040 wort versus a 1.080 wort.

It does seem to provide confirmation that there are diminishing returns, which I don't think any of the IBU formulas account for. We know the calculated IBU figures for Pliny and the othe IIPAs are wildly inaccurate.

How does hop extract work? Is it possible to use hop extract to get more IBUs than you could get by boiling hops?

mabrungard said:

Oh my, there is a lot of crap mentioned in this thread. Its nice that Pliney is mentioned here since Vinnie provides direct confirmation of what I'll tell you here.

Vinnie says that Pliney calculates at an IBU level of way north of 100 (I don't recall what the exact number was) and he has had lab testing performed on many of the beers off the line over the years. He said the typical result was around 75 ppm iso-alpha acids and it may approach 80 ppm.

That result directly from Russian River correlates well with the results that Malowicki and Shellhammer found for alpha acid saturation level in wort. They found the maximum solubility was 80 ppm alpha acid. There is a limit to the conversion of alpha acids to iso-alpha acids of about 90%, so maybe that number that Vinnie mentioned is reasonable.

By the way, in another Thesis by one of Shellhammer's students, the solubility measured for alpha acid solubility in beer is quite low. It was like 10% and we should remember that alpha acids provide little bitterness perception. That paper said that dry hopping adds very little bittering to a finished beer.

So, the comments of 100 to 120 IBUs in beer are pure crap. It has not happened yet and the science says it can't happen.

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?????? Maybe there is a limit to the dissolved IBUs, but you are comparing ppm of dissolved alpha acids to IBUs, and as far as I know, there is no correlation; especially when you toss in a comment on dry hopping which as most people here know adds little if any IBUs to beer.

I think your post possibly adds more ........

the_bird said:

James Spencer had a podcast not too long ago with some scientist, where they experimented to try and determine maximum IBU content. The maximum they were able to measure, in a very simple beer, was ~60IBUs. Not sure whether that result would hold up across a broader experiment (they were only doing a single-hop addition, as I recall, and I think a 1.040-ish wort), but the important takeaway was that there was a sharply reduced amount of extra IBUs being added once you got around 50IBUs; add 50% more hops, you might only go from 52IBUs to 55IBUs, something like that. They did not change the wort gravity - be interesting to see the effect of X amount of hops in a 1.040 wort versus a 1.080 wort.

It does seem to provide confirmation that there are diminishing returns, which I don't think any of the IBU formulas account for. We know the calculated IBU figures for Pliny and the othe IIPAs are wildly inaccurate.

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http://www.basicbrewing.com/index.php?page=radio

Look up IBU ceiling experiment. Even the commercial beers tested came in way lower than their advertised IBUs. The other interesting thing was that the IBUs drop out as the beer ages and 60IBU is probably a more realistic limit.

1 i.b.u = 1 ppm

Calder said:

?????? Maybe there is a limit to the dissolved IBUs, but you are comparing ppm of dissolved alpha acids to IBUs, and as far as I know, there is no correlation; especially when you toss in a comment on dry hopping which as most people here know adds little if any IBUs to beer.

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Sorry to have confused you or any others. It is a leap to talk about alpha acids and IBUs in the same sentence. But the logic that I presented poorly was that: if you can only get about 80 ppm alpha acid into wort and the maximum conversion of that alpha acid to iso-alpha acid is about 90% (both points per Malowicki and Shellhammer), then you are talking about 72 ppm iso-alpha acids (IBUs). This was actual lab analytical data.

Sorry again for throwing in that somewhat unrelated bit about alpha acid in finished beer. The point there was that unconverted alpha acids were proven to add little if any bittering perception to beer. That tidbit came from a Masters thesis by Fritsch under the tutelege of Shellhammer. I believe my original sentences in my original post above do confirm your statement that dry hopping adds little if any IBUs to beer.

Enjoy.

So, if we know 80 ppm is possible in 10 gals of wort, what happens when you boil it down to 5 gals? Does the ppm stay the same, and if so, how is this possible? You would think 160 ppm would result, but apparently this is not the case.

sudsmcgee said:

So, if we know 80 ppm is possible in 10 gals of wort, what happens when you boil it down to 5 gals? Does the ppm stay the same, and if so, how is this possible? You would think 160 ppm would result, but apparently this is not the case.

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Check out the article that SPLASTiK posted the link to. I had the same question, but I read the article, and it makes more sense now. I'll summarize it for you if you don't want to read the whole thing. It basically says that the isomerized alpha acids are degraded over time while boiling. The article suggests that in some cases there is over a 20% loss of isomerized alpha acids over a 90 minute boil.

And not only boiling, but also the difference between wort and finished beer needs to made.

Fermentation also plays a role in reducing measured IBUs. The drop in pH while fermenting and amount of yeast you pitch will affect how much bitterness is retained. As yeast absorb bittering compounds and as the pH drops during fermentation the compounds become less soluble and drop out.

the_bird said:

James Spencer had a podcast not too long ago with some scientist, where they experimented to try and determine maximum IBU content. The maximum they were able to measure, in a very simple beer, was ~60IBUs

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Basic Brewing also did a collaborative experiment with BYO on partial vs full boil worts on March 4th, 2010. They had the actual finished beer IBUs lab tested and found very little difference in IBU utilization, even after diluting the partial boil wort by 50%.

Full pre-boil gravity: 1.068; OG 1.076; IBUs 66
Partial pre-boil gravity: 1.127; OG 1.070; IBUs 61

This pretty well blows a hole in the "100 max IBU theory" as this partial boil must have had well over 122 IBUs in solution after boil. Considerably more in fact, when you consider that yeast pull significant amounts of iso-alpha acids out of solution during fermentation.

This all begins to make sense when one listens to this excellent interview with John Palmer from back in 2008. I believe the homebrewer's 100 max IBU theory actually came from the work of Malowicki and Shellhammer who established that that the maximum solubility of alpha acids in beer is about 90 mg/L. After listening to Palmer's interview however, one will discover that 1 IBU is not equal to 1 mg/L of iso-alpha acid as many homebrewers still believe.

So what is the IBU limit of wort? It's clearly higher than 100, based on the empirical evidence alone. It would make an interesting experiment (master's thesis?) for someone with access to the appropriate lab equipment...

jkarp said:

Basic Brewing also did a collaborative experiment with BYO on partial vs full boil worts on March 4th, 2010. They had the actual finished beer IBUs lab tested and found very little difference in IBU utilization, even after diluting the partial boil wort by 50%.

Full pre-boil gravity: 1.068; OG 1.076; IBUs 66
Partial pre-boil gravity: 1.127; OG 1.070; IBUs 61

This pretty well blows a hole in the "100 max IBU theory" as this partial boil must have had well over 122 IBUs in solution after boil. Considerably more in fact, when you consider that yeast pull significant amounts of iso-alpha acids out of solution during fermentation.

This all begins to make sense when one listens to this excellent interview with John Palmer from back in 2008. I believe the homebrewer's 100 max IBU theory actually came from the work of Malowicki and Shellhammer who established that that the maximum solubility of alpha acids in beer is about 90 mg/L. After listening to Palmer's interview however, one will discover that 1 IBU is not equal to 1 mg/L of iso-alpha acid as many homebrewers still believe.

So what is the IBU limit of wort? It's clearly higher than 100, based on the empirical evidence alone. It would make an interesting experiment (master's thesis?) for someone with access to the appropriate lab equipment...

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Uhh...the references cited do not support your contention that an IBU is not equal to 1 ppm iso-alpha acid. Read here: http://***********/stories/article/indices/37-hops/200-behind-the-ibu-advanced-brewing

That article, which coincides with the interview cited, pretty much confirms that with typically fresh hops, the formulas and analytical results agree. The other component of the interview is that iso-alpha acids are NOT the only bittering components in beer. But, they are the MAJOR bittering components. Beta acids and other components influence the perception of bitterness.

Regarding the Basic Brewing results, I'm not sure how we got from those results to the contention that the partial boil wort had over 122 IBUs in solution after the boil. Clearly advanced math was used that I'm not familiar with. From my read of the Basic Brewing results, the maximum achievable IBU result still appears to be as I originally stated. IBU results in the 60's are significantly less than 75 IBUs.

mabrungard said:

Uhh...the references cited do not support your contention that an IBU is not equal to 1 ppm iso-alpha acid. Read here: http://***********/stories/article/indices/37-hops/200-behind-the-ibu-advanced-brewing

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From the very article you reference:

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.

mabrungard said:

Regarding the Basic Brewing results, I'm not sure how we got from those results to the contention that the partial boil wort had over 122 IBUs in solution after the boil. Clearly advanced math was used that I'm not familiar with. From my read of the Basic Brewing results, the maximum achievable IBU result still appears to be as I originally stated. IBU results in the 60's are significantly less than 75 IBUs.

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So you're implying that plain water has IBUs, or that dilution has no effect on IBUs?

The big thing that I wish someone could examine is IBUs in an unfermented wort versus IBUs in that finished beer. I suspect the latter is quite a bit lower. I mean - the original question, how many IBUs in a wort, is totally different from how many IBUs in a beer, since there's the whole fermentation aspect, time going by for alpha acids to settle, changes in pH, countless other effects. If you've got five gallons of isomerized hop extract, you should be able to make the wort's IBUs whatever you want, but that will not necessarily follow through to the beer.

how does water chemistry factor into the perception of bitterness vs actual IBU or isomerization?

do sulfates for example change the actual isomerization / IBUs (lab tested, not theoretical) or does it simply alter the perception of bitterness?

100% agreed the_bird and terrapinj. Everything about IBUs is ripe for some solid empirical data. One could spend years working out various permutations.

Calder said:

The question is whether you can dissolve more than about 100 IBUs into solution, not whether you can taste them. If you only partial boil it will limit the maximum bitterness you can get in a beer to fairly low.

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I've tasted things (mostly medicine) that have perceived bitterness orders of magnitude higher than any beer I've had. Anyone who things Pliny the Elder represents the maximum bitterness that can be perceived should go chew up a piece of aspirin as I believe that would convince them otherwise.

remilard said:

I've tasted things (mostly medicine) that have perceived bitterness orders of magnitude higher than any beer I've had. Anyone who things Pliny the Elder represents the maximum bitterness that can be perceived should go chew up a piece of aspirin as I believe that would convince them otherwise.

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or anything with wormwood in it.

remilard said:

I've tasted things (mostly medicine) that have perceived bitterness orders of magnitude higher than any beer I've had. Anyone who things Pliny the Elder represents the maximum bitterness that can be perceived should go chew up a piece of aspirin as I believe that would convince them otherwise.

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Or just skim a little bit of the hops off of the surface of a boiling beer and put that in your mouth...