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Old 01-13-2006, 02:54 PM   #1
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Default Do Aroma Hops Add Bitterness?

I've been fiddling with Promash and have found that the Generic setting for hop bitterness actually adds bitterness for additions made at 0 minutes. The others do not. Interesting.......

As I play with this concept in my mind, it would seem logical that near boiling wort (like you would get when you first turn off the burner at 0 minutes) would extract some bitterness from hops added right at flame out depending on how long you steeped them. Certainly not as much bitterness as hops churned in a rolling boil, but certainly some bitterness.

So, for big late aroma additions like in an IPA, are you actually adding bitterness as well? Which IBU bitterness scale should be used? How would you quantify the bitterness imparted by 0 minute additions?

Just a question to ponder......


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Old 01-13-2006, 04:16 PM   #2
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This is bringing up the question of how precise the IBU calculation is to begin with. The only factors, that are uses in the formulas/programs we are using, are gravity, time and amount of a-acid (AA * weight). There are also other factors which are arearently not insignificant. One major other factor is the vigerosity of the boil. This is something that is really hard to measure.

Here is some wisdom I found on a german board posted by a guy who works in a brewery:

"The utilization factor for hop bitterness is difficult to claculate. It will be determined when the breuwery is build and it depends on factors such as geometry of the boil kettle, boil temperature, heating system .... In reality test brews are made that are then analyzed to get the system dependent factor of hop untilization"

He also tested one of his (home brewed) worts and found that his IBU calculations where of by more than 20% !!!

I'd certainly be interested to get some more information on this. Has anybody access to an IBU analyzer and can run some comparisons betwenn actual and expected IBUs?


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Old 01-13-2006, 04:41 PM   #3
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As for bitterness at flameout--I doubt you'd get enough to notice. But I'm no expert.

As for which scale to use--I got this from the greenboard: Use the Tinseth scale for full boils, and the Rager scale for partial boils.

All I've ever used is Tinseth, even when I did extract partials. *shrugs*
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Old 01-13-2006, 04:44 PM   #4
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Intuitively, it seems like the wort would be hot enough to isomerize some alpha acids, but I don't know that enough would be isomerized to matter relative to those that had already been isomerized by the other additions and longer boiling times.
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Old 01-13-2006, 04:51 PM   #5
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don't know if this answers any questions or just re-states the question, but: alpha acids go into sollution ONLY after boiling has isomerized them to iso-alpha acids. their bittering contribution is dependent on the isomerization efficiency in the kettle and the amount and alpha acid content of the hops used. this is the way Greg Noonan puts it in New Brewing Lager Beer.

so, i guess to me, their isn't enough boil time at the 0 min addition to boil for bitterness extraction from the hop. *shrugs also*
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Old 01-13-2006, 05:29 PM   #6
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How about an experiment--boils some water, reduce heat, throw in some hops as you would for aroma, let cool and take a few sips like tea--see if it is more floral or bitter or some combination. A crude experiment no doubt, but sometimes you have to cut through the chemistry with real world testing...
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Old 01-13-2006, 11:38 PM   #7
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At 0 minutes, nil. At 5 minutes, a little. For a low gravity wort the utilization at 5 minutes will be about 0.05 vs 0.27 at 60 minutes. Add to that, typical aroma hops are low AA. I went to a seminar at OSU on "Off flavors" and discovered that, like most people, I have real trouble comparing beers less than 10 IBU apart. I doubt many people would be able to detect the difference in bittering if you doubled an aroma addition.

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