Question: Alpha acid chemistry

I understand that wort is acidic. According to what i've read, I "know" that higher gravity beers have poorer hop bitterness extraction. Bitterness comes from alpha acids, which I surmise are weak acids. So if the gravity of wort were higher, it would theoretically be more acidic, and there for cause lesser alpha acids to disassociate.

As long as this theory is accurate, which it very well may not be, I pose an issue:

Most IBU calculators reduce the IBU # when you add glucose (corn sugar) to the pre-boil recipe. Glucose is a neutral organic compound. It does not contribute any H+ (acidity) to a solution. Why then to IBU calculators reduce the bitterness extraction when glucose is added to the recipe?

My reference for this is beer smith, which dramatically increased the IBUs when I deleted the addition of dextrose.

Is this a falsity in the software, or am I misunderstanding bitterness extraction?

Both.

Software provides an estimate. It's about as accurate as an experienced brewer can do off the top of thier head.

Ph and wort gravity both effect the ability of alpha acids to dissolve. Higher sugar + equal ph = lower IBU.

It used to be thought that hops utilization was dependent on wort gravity, and it even says so in howtobrew.com (by John Palmer). However, in about 2008, Palmer's talk at the NHC backed down from that assertion. The thinking now is that IBUs are independent from wort gravity. I can not remember who he was quoting at the time, but he had gone to a conference in Europe and became convinced that these folks were correct in their belief.

Palmer said that there does to be some difference in utilization at times, but that is due to break material in the wort and not wort gravity. He said he "got it wrong" in the first editions of How To Brew, and will be correcting that.

So there is general agreement now that wort gravity has very little do do with hops utilization. I've seen the spreadsheets and such, but really don't know the science.

Yooper said:

It used to be thought that hops utilization was dependent on wort gravity, and it even says so in howtobrew.com (by John Palmer). However, in about 2008, Palmer's talk at the NHC backed down from that assertion. The thinking now is that IBUs are independent from wort gravity. I can not remember who he was quoting at the time, but he had gone to a conference in Europe and became convinced that these folks were correct in their belief.

Palmer said that there does to be some difference in wort gravity at times, but that is due to break material in the wort and not wort gravity. He said he "got it wrong" in the first editions of How To Brew, and will be correcting that.

So there is general agreement now that wort gravity has very little do do with hops utilization. I've seen the spreadsheets and such, but really don't know the science.

Click to expand...

I've heard BYO did an experiment with hop utilization and wort gravity and discovered the same thing - no effect. It all comes down to boil size.

Can anyone find the reference for the BYO experiment?

KISS Brew said:

I've heard BYO did an experiment with hop utilization and wort gravity and discovered the same thing - no effect. It all comes down to boil size.

Can anyone find the reference for the BYO experiment?

Click to expand...

I think the BYO was a collaboration between BYO (Chris Colby) and Basic Brewing Radio. I seem to remember a podcast from about 2 years ago with that info. If you can't find it, let me know and I'll see if I have it somewhere. James (from BBR) and I had a discussion about it via email at that time, so I could try to wade through some old emails but it would be almost impossible to find.

I don't think there was much science in that BYO experiment, though. I think they did several boils, and tasted them and they were all the same, regardless of boil size/composition of the wort, and that they sent the sample to be tested for IBUs. The results were the IBUs were all about the same I believe, but they didn't go into the "why" and "how" at all.

A better resource might be John Palmer's program from one of the NHC's- I think it was 2008 but am unsure- where he had the slideshow showing the theoretical impacts of increased wort gravity and the actual results. I do NOT have that, and I haven't seen it in a long time.

When asked if there still was a difference in IBUs between higher gravity worts, Palmer admitted that there "probably was" but went on to say that it seems to be related to the amount of break material and not at all related to the actual wort gravity.

Yooper said:

I don't think there was much science in that BYO experiment, though. I think they did several boils, and tasted them and they were all the same, regardless of boil size/composition of the wort, and that they sent the sample to be tested for IBUs. The results were the IBUs were all about the same I believe, but they didn't go into the "why" and "how" at all.

Click to expand...

This sounds like most of BYO's experiments. Thanks for the offer, but don't worry about digging it up.

Yooper said:

A better resource might be John Palmer's program from one of the NHC's- I think it was 2008 but am unsure- where he had the slideshow showing the theoretical impacts of increased wort gravity and the actual results. I do NOT have that, and I haven't seen it in a long time.

When asked if there still was a difference in IBUs between higher gravity worts, Palmer admitted that there "probably was" but went on to say that it seems to be related to the amount of break material and not at all related to the actual wort gravity.

Click to expand...

I'm definitely interested in seeing a source for Palmer's change in thought. I've seen it referred to multiple times on the interwebs, so I believe it, but I'm interested in the details of what he said. Maybe I just have to wait for the 3rd edition of How to Brew.

It sounds like for extract brewers, it all comes down to boil size. For grains, higher gravity is correlated to more break material, which in turn lowers hop utilization.

Sounds like software needs to be updated. Afaik, they all assume lower utilization at higher gravities.

afr0byte said:

Sounds like software needs to be updated. Afaik, they all assume lower utilization at higher gravities.

Click to expand...

Yes, I think so too. But one of the things that I remember discussing was that there really isn't an accurate model to start over with, and that even though it may not be wort gravity that impacts the hops utilization, that it's the best guess as to figure IBUs with what we have at this point.

I think it was Greg Tinseth who I saw discussing this issue, and I think that the Tinseth formula is the best we can do until someone figures a new way to predict probable IBUs.

What I mean is this- when I figure my IBUs, I know what 50 IBUs (Tinseth) in a 1.050 OG beer will be like. It may be a different figure with Rager, so I suggest always sticking with the same scale. The Tinseth scale works pretty well for my AG, low to medium-high OG beers, for me to predict how that beer will come out. Whether it's break material or worth gravity that impacts the utilization rate, it doesn't really matter since you can predict the results.

The problem may come when we try to figure IBUs in an extract batch, especially a partial boil. If IBUs indeed are independent of wort gravity, then no adjustment would be needed. And this works, the vast majority of the time. But in the case of a low IBU beer (say, a cream ale with 15 IBUs), a full boil may change the IBUs a bit due to the lack of much of break material. A difference of 10% isn't a bit significant, but if you get up over 20 IBUs then the beer might be a bit too bitter. That is the only time I can think of when someone may want to consider reducing the bittering hops in a kit beer. If the recipe was designed for all of the extract to be added to a 2.5 gallon boil, and the brewer is doing a 4 gallon boil and adding the extract at the end of the boil, I think the lack of break material for the hops oils to cling to and get "pulled" out may make a difference. Not much- maybe 5-10 IBUs, but that is a big difference when the goal is 15 IBUs.

I think that for the most part, any 5-10 IBU difference is negligible though. In other beers where the typical IBUs are 25+, a 5-10 IBU difference may not even be discernible.

It never made sense to me that higher gravity worts would extract less alpha acids but it would be very difficult to prove or disprove this without a major effort in which, for example, a strong wort were prepared, diluted by various factors, boiled with the same hops from the same batch, pitched and fermented and the final beers analyzed. Not impossible to do but certainly beyond what I can do in my setup.

The next best thing is to record all your hopping and analysis data and try to do a curve fit to an efficiency vs OG plot. I have done essentially that i.e. I have found the parameters of the Tinseth model that best fit my brewing history. But the data is not very useful as the vast majority of the beers I brew fall in a narrow range of OG (12 - 14 °P). Beyond that the variability in malt, yeast and especially hops scatter the data all over the place.

Another source of uncertainty: yes, hops acids are weak acids and thus the amount of dissociation depends on wort pH. There is no reason to suppose that a higher gravity wort would have a higher or lower pH than another similar wort of lower OG but wort pH values to differ and this does have an effect on the degree of isomerization. That is something else that would have to be accounted for.

Yooper said:

...

I think it was Greg Tinseth who I saw discussing this issue, and I think that the Tinseth formula is the best we can do until someone figures a new way to predict probable IBUs.

Click to expand...

I can't say that I've ever tried using Rager for my homebrew (so I can't compare the accuracy in my own beers), but I have to agree that Tinseth seems to match the perceived bitterness in my homebrew when I compare it to a commercial beer that's supposed to have a similar number of IBUs.

...

I think that for the most part, any 5-10 IBU difference is negligible though. In other beers where the typical IBUs are 25+, a 5-10 IBU difference may not even be discernible.

Click to expand...

I can't say for sure (I've never had my IBUs measured/done a triangle test), but I feel like I can sense a 5 IBU difference. However, that's probably largely because I almost always brew beers in the 15-30 IBU range (I like me some Belgian-style beers...I also brewed a cream ale that my wife likes, recently).

afr0byte said:

I can't say that I've ever tried using Rager for my homebrew (so I can't compare the accuracy in my own beers), but I have to agree that Tinseth seems to match the perceived bitterness in my homebrew when I compare it to a commercial beer that's supposed to have a similar number of IBUs.



I can't say for sure (I've never had my IBUs measured/done a triangle test), but I feel like I can sense a 5 IBU difference. However, that's probably largely because I almost always brew beers in the 15-30 IBU range (I like me some Belgian-style beers...I also brewed a cream ale that my wife likes, recently).

Click to expand...

Someone told me that the human tongue can't perceive the difference of 5 IBUs (maybe Jamil z? John Palmer?) but I would say that just based on my own experience I can easily tell a 15 IBU beer from a 20 IBU beer. But in a 50 IBU APA vs a 57 IBU APA? not so much. So I think you're on to something there.

Another thing is that an IPA has lots of things going on- firm malt backbone, firm bittering, lots of late hops. So even a 10-15 IBU difference may not have much have a taste impact, say 62 IBUs vs. 75 IBUs.

In a cream ale, though, when you simply have just enough bitterness to counter the sweetness of the malt, and so it's a balanced beer (perhaps leaning toward sweet), a small difference of 5-10 IBUs may very well be a huge difference.

According to these study's, utilization is more dependent on pH and boiling time than gravity. Utilization even increases in lower gravity wort for Magnum and Perle hops (in 2nd study), and shows little or uneven utilization for Aurora and Warrior in 1st study.

http://journals.usamvcj.ro/agriculture/article/viewFile/876/873
http://journal-of-agroalimentary.ro/admin/articole/99614L13_Mudura_Elena_249-252.pdf

As for IBU threshold, R. Daniels in his book says that we cannot perceive less than 5 IBU difference, but I agree with Yooper, it is somewhat different if it is 50-55 or 15-20 IBUs.

I heard Jamil Z talking about the gravity effect on hop utilization on a Brewstrong episode years ago. I recall that he cited a study that suggests that its not so much the gravity and increased sugar content itself that causes the reduction in utilization, but that the increased uptake and removal of the bittering compounds by the flocculated yeast. That makes sense to me. But the correllary with reduced utilization and increased gravity is still good, no matter the mechanism.

I'm on board with Yooper on the magnitude of the bittering having more to do with the perception of a 5 IBU bittering difference. It should probably be expressed as a percentage 55/50 = 10% increase vs 20/15 = 33% increase.