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Old 03-15-2011, 09:28 PM   #1
Dennisusa
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Can anyone give me the formula for bittering effect when adding hops after the boil? All the formulas seem to require OG, Alpha content & boil duration, but adding a mountain of hops after flame-out (during the swirl) would seem to me to be adding IBU's as well. At least that's what I suspect. But without good data and a formula, how do we measure this? In the absence of hard data I'm not persuaded that with a steep time of, say, 30 minutes (during cool down from 205 to 180F) we would not be adding significant IBUs. And if it does, we ought to be able to calculate this.

 
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Old 03-15-2011, 09:31 PM   #2
juslod
 
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If I have understood completely, the oils that add bitterness in hops are only extracted when at boiling temperatures. Just adding a bunch at flame out wouldn't add any IBUs.

May I ask why you would want to do this, anyway?

 
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Old 03-15-2011, 09:41 PM   #3
Golddiggie
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From my understanding, only when the hops are boiled will you extract the bittering oils from them. Otherwise you'll just get aroma, and maybe a bit of flavor...

There's a couple of chapters in Designing Great Beers going over hops... You might want to read through them so that you have a better understanding of what's going on... I'm not about to start typing it all in for you... Suffice to say, no boil temp, no bitterness from hops.

The oils/compounds that create the bitterness are not only extracted, but changed into what produces the bitterness during the boil...
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Old 03-15-2011, 09:48 PM   #4
BendBrewer
 
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Short answer is no, post Knock Out additions do not increase IBUs.

They add great aroma though.

 
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Old 03-15-2011, 09:51 PM   #5
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Hey Bend... I've not dry hopped yet, but planning to on a brew started last week... Do you get ANY flavors from the dry hops (whole leaf in my case) or is it just all aroma?? I know that taste and smell are closely linked senses, so I was hoping that some would carry through into flavor...
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On Tap: Caramel Ale, Mocha Porter II, MO SMaSH IPA
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Old 03-15-2011, 09:55 PM   #6
Dennisusa
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Very fair questions, Juslod.

I accept that isomerization maximization occurs with a 60-minute rolling boil (I've seen the IBU graphs that prove the alpha utilization curve), but I find it hard to believe no IBU's are added after the boil whatsoever. That just does not sound right - especially with an extended steep period. We all seem to accept this truism, but I've never seen an IBU graph that demonstrates no bittering effects without a boil. Yet tea made out of even one lonely hop petals steeped in (unboiling) hot water can be awfully bitter.

My question comes from wondering if: (a) bittering components are maximized with extended alpha isomerization during a long boil and (b) flavor/aroma components are maximized after the boil or during the secondary fermentation, what does adding hops 15 minutes before the end of boil do that would not be better accomplished by slightly more bittering hops at the beginning and slightly more aromatic hops at flame-out would not do even better?

Just asking.

 
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Old 03-15-2011, 10:04 PM   #7
Dennisusa
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Humans can detect only 5 flavors: sweet, sour, bitter, salt, and umami. All other "flavors" are apparently just aromas in some combination with one or more of those five flavors (hence when you catch a cold food taste flavorless).

 
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Old 03-15-2011, 10:16 PM   #8
scottland
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I'm going to disagree with what's been said above. You can still extract alpha acids and impart biterness in beer at temperatures below boiling. This all depends on how quickly you chill your wort, but I definitely believe that IBUs are extracted during the 160-200* range. Not as much as if it were boiling, but it happens.

 
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Old 03-15-2011, 10:18 PM   #9
Dennisusa
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Thanks, Scotland, I was feeling rather lonely there. Do you have a "steep time" graph or any other hard data that measures this?

 
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Old 03-15-2011, 11:18 PM   #10
erikpete18
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Well, since I'm bored at work, I thought I'd do a little digging since your theory makes sense. Here's an article you might be interested in http://pubs.acs.org/doi/abs/10.1021/jf0481296. In case you can't access it, the basic idea is that they took alpha acids at a variety of different concentrations, heated them to different temps, and measured the resulting effects on isomerization.

Table 1 says that to achieve 60% alpha acid to isoalpha acid conversion, you've got to boil it for 90 minutes (100C). Since I don't want to look up what the formula for isoalpha acid to IBU conversion is, let's assume that this is a pretty good reference point for a normal wort. At 90C (194F), it takes about 3.5 times as long (207 min.) to get the same conversion. Not sure if we can assume that the isomerization is linear across time, but a rough guess would be that you'd have 3.5 times less isomerization at 90C than you would at 100C.

From there, if you figure this 3.5x decrease, plus the amount of time that your wort is actually at 194F and the resulting exponential decreases as temp decreases, I think you're probably right that some of the alpha acids are still undergoing isomerization, especially if you do no-chill and let your wort chill down over time without any cooling attempt.

However, in the grand scheme of things, this likely makes up far less than 5 IBU (unless you're throwing in a pound of hops at flame-out) which is about the differential we can detect with taste. Of course, the iso-alpha acids aren't the only bittering components in hops, but that's a whole other set of experiments!

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