[denny]

I seem to remember that in the last year or so there was some info that contradicted the long held belief that hop utilization is affected by boil gravity.  However, I haven't been able to turn anything up.  Does this ring a bell for anyone or am I delusional?

[HoosierBrew]

I remember a posted link to that effect. I haven't been able to find it yet.

[JJeffers09]

The only thing I know of utilization is from glenns research. Pretty straight forward calculations
Mg/l utilization  = (.AA*oz*7490)÷Gallons of wort
With the gravity or "bigness factor" of
Bigness factor = 1.65*0.000125^(OG-1)
Then boil time of
Boil time factor = (1-e^(-0.04*boil time))÷4.15
Utilization = bigness factor * boil time

That's based on Glenn's research realbeer.com

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[denny]

The only thing I know of utilization is from glenns research. Pretty straight forward calculations
Mg/l utilization  = (.AA*oz*7490)÷Gallons of wort
With the gravity or "bigness factor" of
Bigness factor = 1.65*0.000125^(OG-1)
Then boil time of
Boil time factor = (1-e^(-0.04*boil time))÷4.15
Utilization = bigness factor * boil time

That's based on Glenn's research realbeer.com

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Thanks, I'm familiar with that.  What I'm thinking of was more recent.

[JJeffers09]

I have not seen bigness factor debunked so I guess I am at the kids table right now...

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[denny]

I have not seen bigness factor debunked so I guess I am at the kids table right now...

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I'm not 100% sure it has...just kinda remember something...

[dmtaylor]

I've never heard of such a thing.  However my intuitive side tends to think it is plausible that isomerization might be independent of gravity.  Personally I would theorize that sustained high temperature (boiling) is more important than gravity of the medium.  Solubility might come into play at the 90-100 IBU speed of light type limit, e.g., if adding a buttload of hops to a concentrated boil, you can only get so much IBUs, which then when diluted with more water will tend to reduce the total IBUs.  So there's likely some effects at very high IBUs with concentrated boil later diluted.  But for any reasonable hopping levels of non-IPA, non-RIS, etc. without subsequent dilution, I wouldn't think the effect significant.

Just thinking out loud.  No, I don't have any objective evidence at this time to support my intuitive hypotheses.

[kramerog]

My recollection is that the the explanation of why hop utilization varies according to gravity changed.  I can't be any more specific.

[denny]

I found a post here on the forum that John Palmer might have said it, so I've got an email in to him.  I'll update with what (if anything) I hear.

[denny]

My recollection is that the the explanation of why hop utilization varies according to gravity changed.  I can't be any more specific.

One supposition was that higher gravity wort creates more break, which is the issue rather than the gravity itself.  Dunno...

[denny]

I've never heard of such a thing.  However my intuitive side tends to think it is plausible that isomerization might be independent of gravity.  Personally I would theorize that sustained high temperature (boiling) is more important than gravity of the medium.  Solubility might come into play at the 90-100 IBU speed of light type limit, e.g., if adding a buttload of hops to a concentrated boil, you can only get so much IBUs, which then when diluted with more water will tend to reduce the total IBUs.  So there's likely some effects at very high IBUs with concentrated boil later diluted.  But for any reasonable hopping levels of non-IPA, non-RIS, etc. without subsequent dilution, I wouldn't think the effect significant.

Just thinking out loud.  No, I don't have any objective evidence at this time to support my intuitive hypotheses.

You're correct that isomerization is temp dependent.  But then there's the issue of getting those isomerized acids into the wort.....maybe.  I'm guessing, too!

[denny]

OK, looks like my last post was pretty much on..here's the response from John...

"They are indirectly connected. The sugar concentration does not affect the solubility of the isomerized alpha acid at parts per milliion. To put it another way, increasing the IBUs by a factor of 100 doesn’t make a blip in the overall gravity of the wort. Therefore the gravity of the wort doesn’t affect the solubility of the iso-alpha. Instead, the reason that higher wort gravity affects hop utilization is because higher wort gravity means more protein, therefore more hot and cold break, and higher yeast mass to be pitched, and these are the factors that carry isomerized alpha acid (and plain alpha before it can be isomerized) out of solution. In other words, wort gravity does not affect hop isomerization, but it does effect alpha acid and iso-alpha loss at various points in the brewing process."

[dmtaylor]

You're correct that isomerization is temp dependent.  But then there's the issue of getting those isomerized acids into the wort.....maybe.  I'm guessing, too!

But where are the isomerized acids gonna go if they don't go into the wort?  Oily scum on the sides of the kettle (like the HopShot)?  Just magically not show up in the wort that they've been boiled in?  I have my doubts.  Some insoluble amount might fall out as trub in the fermenter I suppose, but at least initially would be suspended in the wort.

Anywho, I'm just talking in circles now.  Someone is bound to turn up the answer in a few more minutes.

EDIT: Yep, now I see the above post, and it makes good sense.  More protein gunk in the wort and more yeast to floc out removes more of the acids.  I can kind of see that.

[JJeffers09]

When I read that Denny I get it does but it doesn't therefore it does and in conclusion other processes create iso-alpha loss... so I am at a loss

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[dmtaylor]

When I read that Denny I get it does but it doesn't therefore it does and in conclusion other processes create iso-alpha loss... so I am at a loss

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The key takeaway is that it's not the gravity that affects utilization, but rather protein.  If there was some way to have all the sugar without the protein, you could improve utilization.  For example, an all-malt wort of SG 1.060 (or pick any number) might have less utilization than a wort with an equivalent SG 1.060 (or whatever) but with 20% cane sugar to 80% malt, because cane sugar has zero protein.  Interesting...