Author Topic: No Increase in IBUs When Boil Time Exceeds 60 Minutes  (Read 5349 times)

Offline durrettd

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No Increase in IBUs When Boil Time Exceeds 60 Minutes
« on: June 17, 2015, 11:20:36 PM »
I assume I should see an increase in the IBUs from a hop addition when I increase the boil time beyond 60 minutes but I don't see that. Do I need to adjust something or does boiling beyond 60 minutes really not give me more IBUs?

Dan

Offline brewfun

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Re: No Increase in IBUs When Boil Time Exceeds 60 Minutes
« Reply #1 on: June 18, 2015, 12:25:13 AM »
It may depend on the formula you're using. It may also depend on the AA% and amount of hops you're using.

On a practical level, about 90 minutes in and you begin breaking as many isomers as you create. Often, the IBU contribution past 60 minutes goes pretty flat, resulting in only a couple more IBUs rather than a more linear rise. I know that Tinseth accounts for that plateau.
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Offline jtoots

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Re: No Increase in IBUs When Boil Time Exceeds 60 Minutes
« Reply #2 on: June 18, 2015, 07:38:04 AM »
i'd be curious as to why first wort hopping contributes more IBUs if a longer boil does not.

Offline Oginme

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Re: No Increase in IBUs When Boil Time Exceeds 60 Minutes
« Reply #3 on: June 18, 2015, 09:23:03 AM »
The thought with the additional bitterness obtained from first wort hopping is that more of the volatile alpha acids are retained and isomerized at the lower temperatures of the wort leading up to the boiling point. Normally, they would get blown off when added at the boiling point much faster than they can be isomerized.

 
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Offline jtoots

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Re: No Increase in IBUs When Boil Time Exceeds 60 Minutes
« Reply #4 on: June 18, 2015, 09:28:59 AM »
The thought with the additional bitterness obtained from first wort hopping is that more of the volatile alpha acids are retained and isomerized at the lower temperatures of the wort leading up to the boiling point. Normally, they would get blown off when added at the boiling point much faster than they can be isomerized.

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Offline durrettd

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Re: No Increase in IBUs When Boil Time Exceeds 60 Minutes
« Reply #5 on: June 18, 2015, 01:25:54 PM »
+1 for Oginme and brewfun! Those explanations make a lot of sense. I've played around with a couple of recipes and I'm seeing the effects Brewfun described.

I had never heard an explanation of the effects most people observe with FWH; I had always assumed it was just another miracle that would never be explained.

Thanks!

Dan

Offline MaltLicker

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Re: No Increase in IBUs When Boil Time Exceeds 60 Minutes
« Reply #6 on: June 18, 2015, 05:08:42 PM »
All true, and interestingly, most describe the perception of bitterness from FWH to be smoother, even lower, than regular.  I always FWH the bittering hops, and eventually changed the BS default setting on FWH utilization from +10% to -10% to account for the softer bitterness.   Hoppy beers started hitting the appropriate expected bitterness after that. 

Offline jtoots

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Re: No Increase in IBUs When Boil Time Exceeds 60 Minutes
« Reply #7 on: June 19, 2015, 07:16:48 AM »
I always FWH the bittering hops, and eventually changed the BS default setting on FWH utilization from +10% to -10% to account for the softer bitterness.   Hoppy beers started hitting the appropriate expected bitterness after that.

Interesting move for sure.

Offline brewfun

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Re: No Increase in IBUs When Boil Time Exceeds 60 Minutes
« Reply #8 on: June 19, 2015, 09:43:29 AM »
For those that like to look at the research behind the math, here is Glenn Tinseth's page:

http://realbeer.com/hops/research.html

The graph is pictured below.

For FWH, the perception doesn't meet the reality. You may perceive less bitterness, but there are actually more IBUs present. However, y'all know that I am quick to point out that IBUs don't equate to your bitterness perception. Rather, it's the alpha acid ratios and how they isomerize that make up what you perceive.

Dave Green wrote about it for BYO in 2014:
Quote
So why does first wort hopping work? That is still not fully understood according to my research. All I can do is offer some theories as to why it provides a smoother bitterness. There are three primary alpha acids found in hops: humulone, cohumulone and adhumulone. Relatively, they are not that bitter, but when heated above about 175 °F (80 °C) they will isomerize (re-arrangement of the molecule) into iso-alpha form: iso-humulone, iso-cohumulone and iso-adhumulone respectively. At this point they are several times more bitter than their non-isomerized cousin. In the isomerization process each alpha acid is further divided into the cis and trans states. This is akin to left-handed vs. right-handed states; they are mirror images of each other, just flipped. Each of those forms acts slightly differently as well. Another factor that could play a key role here are hop glycosides which have been the focus of many discussions surrounding misunderstood components of hops. So why am I explaining all this? Well just to show that there is a lot going on in the bittering process. Add in beta acids plus oxidative reactions that are occurring on the various oil components and you can see that complex nature at a molecular level in your wort when hops are added.

Full article here: https://byo.com/grains/item/2958-pre-boil-hopping

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