IBU Clarification

Correct me if I am wrong but IBUs (International Bitterness Units) refer to the hops that have been in the boil longer than 30 minutes and contribute to the bitterness of the beer. If you add 6 ounces of hops in the last 5 minutes they will not contribute to the IBUs, but flavor and aroma, correct? Or am I way off base here?

hypergolic said:

Correct me if I am wrong but IBUs (International Bitterness Units) refer to the hops that have been in the boil longer than 30 minutes and contribute to the bitterness of the beer. If you add 6 ounces of hops in the last 5 minutes they will not contribute to the IBUs, but flavor and aroma, correct? Or am I way off base here?

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Not "way" off, but the longer the hops are in the hot wort the more alpha acids will isomerize and bitter your beer. Even hops tossed in at flameout have a few minutes at 200F+ and will contribute some bitterness but more to the flavor/aroma side as you suspected.

It's not that simple. As long as you are boiling, you are getting IBUs out of the hops. While you are boiling, you are losing the aroma/flavor compounds. Here's a chart that might help.



In short, you are going to get IBUs and bitterness out of late additions. This is what hopbursting is all about. I make pale ales with hops added only in the last 15 minutes and they turn out great.

That chart is very helpful, thank you IffyG. Let me phrase this another way, say I have a beer and on the label it say 100 IBUs can that be a good indicator of how much flavor and aroma hops will be in the beer?

Nope. BJCP guidelines for a given style would probably reveal more. To my knowledge there is no standard for measuring hop flavor and aroma other than on a scale from none to a lot

Nope. You can have a super high IBU beer that will have little to no aroma or flavor if the hop additions were all early in the boil. Aroma and flavor compounds are quite volatile and make their way out of the boil fairly quickly.

Not really. If they got all their IBUs from a single 60-minute addition, there will be no flavor or aroma to speak of. It's not likely that's how it was brewed, but it's possible.

IffyG said:

Nope. You can have a super high IBU beer that will have little to no aroma or flavor if the hop additions were all early in the boil. Aroma and flavor compounds are quite volatile and make their way out of the boil fairly quickly.

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+1. As an example, you can have a stout with fairly high IBU's, but there is almost no hop flavor/aroma in many stouts...which is desired for the style. If you look at a recipe for a stout, almost all the hop additions will be toward the 60 minute range giving you the bitterness with no flavor.

Thank you, you all answered my question.

jeffjm said:

If they got all their IBUs from a single 60-minute addition, there will be no flavor or aroma to speak of.

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I disagree. If I add 35ibu worth of Magnum to one beer, and 35ibu worth of Simcoe to another, you'll definitely notice the difference. It won't be a strong difference, but it's there. People would simply bitter every beer on earth with Magnum or Warrior if that was the case.

I feel the same way for that chart. It just generalizes the process too much. You get hop flavor and aroma when hops are added anywhere inside 20minutes. You also get hop aroma and flavor for additions longer than 20minutes, it's just not as much.

The chart should really look much more like this. Excuse my crude 30sec paint drawing.