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The prevailing wisdom seems to be that dry hopping is for aroma only, and effects on flavor are assumed to be a matter of perception. (i.e. smell affects taste)

However, while attempting to "fix" a beer that came out far too sweet, I have been looking into hop extracts, etc. While researching I came across this message:

From a chemical point of view, dry hopping will extract all of the alpha and beta acids in hops. The humulones, lupulones and other volatile oils are isomerized in the alcohol and water (the alcohol dues most of the extraction). Yes, more aroma and flavor will be extracted, but so will bitterness. We dry hop most of the time to add aroma to the beer, so most of the time we dry hop with low alpha acid "aroma" hops. Try dry hopping with Galena, Perle, Simcoe, Challenger, Northern Brewer or other high alpha acid hop. You will get the bitterness!

Is this true? Will using high-alpha hops for dry hopping contribute bitterness?

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Meant to include the source of that comment: groups.yahoo.com/group/Zymurgy/messages/… –  Dustin Rasener Nov 14 '11 at 21:07
    
Thanks for that. The whole part up to the parenthesis is bogus. –  BeerSensor Nov 21 '11 at 14:56
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2 Answers

up vote 13 down vote accepted

That quote you posted is a mess. I don't even know what they're trying to say there.

Yes, dry hopping will add bitterness, but not in the usual sense (which is iso-alpha acids). Dry hopping is done cold, so there is essentially no isomerization of alpha acids going on, which is what normally happens in the kettle boil. The bitterness that comes from dry hopping is mostly from polyphenols. The polyphenols of low-molecular weight will add bitterness (catechin, epicatechin, procyanidin, prodelphinidin, etc), while the higher molecular weight polyphenols (tannins) will add astringency.

Beer Sensory Science, Bitterness

Beer Sensory Science, Astringency

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So it seems that the salient point is that, while alpha acids may be extracted from dry hopping, they will not be isomerized thus they will have no effect on bittering. –  Dustin Rasener Nov 14 '11 at 22:32
    
That is correct, although not many alpha acids will be extracted into a cool aqueous product. They are very hydrophobic, so they don't like to be in water. As I said, most bitterness resulting from dry-hopping comes from polyphenols. –  BeerSensor Nov 15 '11 at 16:30
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I love science. :) –  Dustin Rasener Nov 17 '11 at 23:00
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I've recently done the experiment. Zero boil hops, but dry-hopped with 6 ounces of high alpha acid hops (Summit, Simcoe and Apollo). This brew is quite bitter, whatever the reason, and it is of the same "kind" of bitterness one would expect from hopping in the boil and not particularly astringent.

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Very interesting! I'd love to know if this is verifiable and what compounds might be causing the bitterness. –  bk0 Sep 27 '12 at 14:56
    
Well this is confusing, I'm not sure what the answer is now. –  Another Compiler Error Mar 3 at 16:46
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