IBU data for split batch

[stickyfinger]

I just analyzed a batch of beer for IBUs for the first time and thought I'd share the information, which I found intriguing. I've never done it before, though I could have done it for years. I should have done it earlier!

Anyway, I made a 10 gallon batch using

16.3 lb German Pils
1.44 lb Caramunich 60L
0.48 lb Caramunich 120L
158F mash for 45 minutes

I boiled for 90 minutes and added 3 ounces of 3.1% AA Saaz whole cone hops for the entire boil. The hops are at least 2 years old but have been kept cold in the freezer. The boil was gently bubbling with moments of almost still interspersed with big belches of bubbles. Boil off was around 12% per hour.

I fermented half with Safale S-04 and half with Danstar Belle Saison (for fun)

OG was 1.046
FG S-04 was 1.013
FG B.S. was 1.004

At 18 days since brewing the beer, both are now in kegs and clearing slowly. The calculated IBUs from the Rooftop IBU website are 17.1.

The actual IBUs of the S-04 beer are 13.4
The actual IBUs of the Belle Saison beer are 16.9

So, it seems that the IBU calcs are pretty accurate, and the hops have maintained pretty good potency (though, I have to do more tests to see if things keep making sense.)

I thought it was interesting that the IBUs differed between the two beers. I had assumed it would be independent of yeast, then I found this article:

http://beerandwinejournal.com/yeast-strains-ibus/

I have no idea why one yeast would result in more IBUs than another. It's interesting. I thought it might have to do with flocculation effects at first, but they said wheat beer yeasts drop the IBUs a ton and a low flocculation yeast like WLP001 doesn't drop the IBUs well at all.

Anyway, just some interesting information.

On a side note, I tested some Dogfish Head 60 minute IPA and found that it had 34 IBUs yet is rated for 60 IBUs. Redhook Hop Hammer IPA tested at 42 IBUs and is listed at 44 IBUs. Lagunitas Hop Stooped tested at around 66ish IBUs and is listed at 102 IBUs. I don't know how old the beers were.

 

[jtdrowns]

Cool info. What are you using to test the IBUs with?

 

[zwiller]

Thanks for posting. Interesting info. To add some data to your results, I just did my first batch where I used an online calculator to estimate AA loss for some older hops and I do NOT like the results and the resulting beer is too bitter. I think my results are similar to yours and the AA degradation is negligible and will just use the stated AA as is and not adjust in the future. For the record, I am talking unopened 1oz packages store in the freezer, but I suspect an opened package reasonable sealed in a freezer would not vary much either.

 

[ajdelange]

Interesting results. The reason yeast effect bitterness is that they adsorb some of the bitter acids to their surfaces and different strains do this more or less than others.

I would guess based on memory that the differences between calculated and measured IBUs in my experience would rms at about 5-6 IBU. The commercial brewer signs a contract with the hop supplier and in the fall a bale of hops arrives. He brews with it, has some analyses done, tweaks the schedule, goes back for a second (or additional) round of analysis and then uses that same bale for throughout the rest of the year dealing only with the gradual decline in potency upon which he can check with additional analyses. Even if his analysis instrument is a taste panel things are under control for him. The homebrewer never really knows what he is getting. Packages aren't even marked with harvest year. Even if he gets hops from the same packager from the same lot the individual packages may have been handled very differently. Then brewers vary their process a lot. This effects utilization. Some models (Tinseth) have process related variables that you can tweak but how to tweak them?

 

[stickyfinger]

zwiller,

i started just using the published value until i see that my ibus vary a lot. i can measure all of my beers now!

 

[stickyfinger]

Cool info. What are you using to test the IBUs with?

I used the ASBC method with octanol/isooctane extraction and then measured the absorbance at (I think it was 275nm).

 

[stickyfinger]

Interesting results. The reason yeast effect bitterness is that they adsorb some of the bitter acids to their surfaces and different strains do this more or less than others.

I would guess based on memory that the differences between calculated and measured IBUs in my experience would rms at about 5-6 IBU. The commercial brewer signs a contract with the hop supplier and in the fall a bale of hops arrives. He brews with it, has some analyses done, tweaks the schedule, goes back for a second (or additional) round of analysis and then uses that same bale for throughout the rest of the year dealing only with the gradual decline in potency upon which he can check with additional analyses. Even if his analysis instrument is a taste panel things are under control for him. The homebrewer never really knows what he is getting. Packages aren't even marked with harvest year. Even if he gets hops from the same packager from the same lot the individual packages may have been handled very differently. Then brewers vary their process a lot. This effects utilization. Some models (Tinseth) have process related variables that you can tweak but how to tweak them?

I guess the next thing I should do then is to analyze my hops. I can get the %AA with UV as well.

 

[zwiller]

Cool stuff. It does seems like hop technology is overdue for an upgrade, or that the prices need to come back down to $10/lb . That said, it does seem that since the hop shortage in 2008 we are at least becoming more aware of the harvest year and most LHBS I've been to are storing hops properly. Years ago, I saw some pretty sad stuff...

Sticky, I hope you gather some good data!

 

[ajdelange]

I guess the next thing I should do then is to analyze my hops. I can get the %AA with UV as well.

I've never gotten the feeling that that MOA is the most robust in the book. I've done it a couple of times as for example when my club made a 'hop buy' and we had little idea as to what the actual AA content might be. The procedure is a bit tricky with on the fly dilutions to get the absorption in the right range and the results I got did not give me very good predictions of the bitterness of the beer made with those hops. Perhaps had I stuck with it and gotten the procedure down better I would have gotten better results. The message here being that if you get funny answers at first, stick with it.

 

[stickyfinger]

I've never gotten the feeling that that MOA is the most robust in the book. I've done it a couple of times as for example when my club made a 'hop buy' and we had little idea as to what the actual AA content might be. The procedure is a bit tricky with on the fly dilutions to get the absorption in the right range and the results I got did not give me very good predictions of the bitterness of the beer made with those hops. Perhaps had I stuck with it and gotten the procedure down better I would have gotten better results. The message here being that if you get funny answers at first, stick with it.

Thanks for the info. I'll keep that in mind. I'll have to see how the results were for some samples a friend of mine just ran on a bunch of different commercial hop samples to see how well they correlated.

 

[ajdelange]

I'd be interested in seeing that data.