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Home Brew Forums > Home Brewing Beer > General Techniques > Partial boils - latest Basic Brewing Radio podcast
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Old 03-04-2010, 02:44 PM   #1
uncleozzy
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Default Partial boils - latest Basic Brewing Radio podcast

Hope I didn't miss a thread about this, but has anybody listened to the latest Basic Brewing Radio podcast? The topic is the result from the BYO partial boil experiment, comparing hops utilization and color differences between full boil, partial boil, and partial boil with late extract addition in extract and PM brewing.

The results--as tested by a lab--are really surprising. Despite boil gravities of 1.068, 1.127, and 1.077, respectively, the measured IBUs in the fermented beer were roughly the same (about 60, give or take; the BU:GU was the same in all three).

What does this do to our ideas about hops utilization, when you can get, essentially, similar bitterness in 1.100+ wort as in sub-1.070 wort? Tinseth's table, for example, shows 36% less utilization for a 60-minute charge in a 1.120 wort vs. a 1.070 wort.

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Old 03-04-2010, 02:56 PM   #2
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John Palmer talked about this on BBR a couple of years ago as well.

http://media.libsyn.com/media/basicb...3-20-08ibu.mp3

His conclusion was that the trub takes out some of the bitterness, so the higher gravity gets you more trub which gets you less bitterness. This would only hold true for all grain, as extract already has a lot of the proteins removed.

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Old 03-04-2010, 03:15 PM   #3
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SumnerH started/spearheaded some great discussion on this about this time last year. Here is one thread.

Here's the micro-cliff-notes:

Quote:
1. The rate at which alpha acids isomerize is pretty constant in worts of various densities. That is, the gravity of your wort has almost zero impact on how much hop utilization you get. But:
2. Isoalphas cling to everything, including hot break. So there's an indirect effect where higher-gravity boils are likely to lose more isoalphas in their (correspondingly greater) hot break material.
In another thread SumnerH said:
Quote:
Tinseth is one of the better ones. Don't trust any of them too much for:

1) wheat/rye beers
2) partial boils or late-addition boils (if they try to "properly" account for those, they'll wind up _way_ off)
3) beers with added sugar (cane, corn, Belgian candi sugar or syrup, whatever)

The #1 incorrect assumption most of the algorithms make is that the gravity of the boil affects hops utilization. It doesn't, though the amount of break material (which is often but not always correlated with gravity) does. The above 3 cases are the ones where that assumption is most egregiously wrong.
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Old 03-04-2010, 03:27 PM   #4
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Ah, interesting! (I'm clearly behind-the-times a bit; I'll have to read through that thread.) And doubly-interesting, I suppose, because, in the experiment, they made a serious effort to keep trub out of the fermenter.

I wonder, then, if dumping all the break material in the fermenter would make those AAs "available" to the beer through the churning of fermentation (and maybe the solubility of ethanol?), or if they're just "stuck" to the break material.

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