I know that dry-hopping does not isomerize (is that the right word?) the alpha acids in the hops. My question is: are the alpha acids still in the hops afterward or are they extracted. I have once in the past pulled the hop sack from the empty keg and put it into the freezer. I used it as part of the bittering addition for my next batch. I figured that the flavor and aroma were gone from the dry-hopping (but I would lose them anyway in an hour boil) while the bittering might still be available. Any thoughts?
I’d guess that a majority, if not all, the alphas are intact. At the very least, they won’t be isomerized, which is what creates bitterness. I think if I was going to try this, I’d want to time it so that I could reuse the hops the same day they were pulled from dry hopping. I have nothing to base that on other than a gut feeling, but I’ve got a big gut…
Although the alpha acids won’t be as soluble since they haven’t been isomerized, that won’t stop the lupulin from falling to the bottom of the fermenter. Your bag might, and the hop mass will stop some, but my guess is you’ll lose some. I have no idea how much though. I don’t see any problem with doing it, especially if you’re brewing the same day you remove them or you freeze the whole bag after removing it from the the beer. I haven’t done it though, so those are just my thoughts on the subject.
Good point on the lupulin that I hadn’t thought of. I should have, since a lot of my dry hopped beers end up with a layer of lupulin on the bottom of the glass.
Mine too, at least for the first pint or two (or five) out of the keg 
My wife complains that the beer isn’t as good after the lupulin goes away.
That’s not surprising
I reused once after a dry hop. Noticed X ounces of used does not equal X ounces of fresh for bittering purposes. That was back during the massive hop-scare.
Thanks, this all pretty much confirms my line of thought. Some, if not most, bitterness should still be available for later use. It will be hard to calculate in advance.
BTW, Denny, It’s your cascades that are in question here.
Well, those are an unknown AA anyway, so I’d say assume they’re 5%, deduct 20% after dry hopping (a total WAG!), and try bittering with 'em. Heck, no matter what, you’ll make beer!
This idea seems ideal for FWH type work. That way you aren’t relying entirely on their variable addition of
bitterness, no?
That’s my ROT WD, FWH is the way to go for spent dry hops. I use them mostly in IPA’s and don’t even consider any potential IBU’s with them. The bitterer the better :
Can we please throw more abbreviations into our posts?
I currently understand way too much of what everyone is saying.
Me too! 
ROTFL
Wish I could remember the exact specs, but some big guys did this experiment during Hop Crisis 07 and concluded that recycled dry hops’ bitterness potential was reduced by 30% (not bad on the WAG Denny)
Drew,
OT but, I love the name of your Old Ale…and being that you are a new homeowner…I’d hold off from imbibing on that one…haha 
Thanks… first glass is scheduled to pour on October 6th 2011
Since my next brew is one where I am not so concerned with the bitterness level (it’s a double red ale so anywhere from about 40-65 IBUs is ok with me), I am going to try this out. I have 50g of Amarillo dry hopping my Belgian IPA.