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	FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
		Digest Janitor: pbabcock at hbd.org


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Contents:
  Over-Carbonation? Fermentation Re-Start Question ("John W. Zeller")
  Bulging kegs? ("Spencer W. Thomas")
  Re: Over-Carbonation? Fermentation Re-Start? (Calvin Perilloux)


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Date: Tue, 18 Jan 2011 23:59:39 -0500
From: "John W. Zeller" <jwzell at cincic.com>
Subject: Over-Carbonation? Fermentation Re-Start Question

Trish requested opinions on why her mini-kegs are bulging from excessive 
carbonation when only a minimal amount of priming sugar was used.  My 
guess would be that there was a substantial amount of residual CO2 in 
the beer when it was kegged.  The Octoberfest mentioned is a lager, so 
it would typically be fermented at about 50F usually fallowed by an 
extended lagering period at much colder temperatures.  A diacetyl rest 
at near room temperature for 4-6 days should allow most of the residual 
CO2 to dissipate, but if the diacetyl rest was skipped and there were 
some residual sugars remaining in the beer going int lagering, then much 
the CO2 could still be in the beer when it was kegged.  The CO2 
generated by the yeast while consuming the priming sugar plus the 
residual CO2 could be enough to bulge the kegs.  The excess CO2 had to 
come from somewhere and I can only conclude that much of it was already 
in the beer when it was kegged as you indicated that the fermentation 
had finished out normally.  Give us more detail on your temps during 
fermentation, diacetyl rest and lagering period and we might be able to 
spot something.  Also, what was your F.G.?  If it was unusually high it 
could be an indication that the fermentation had not finished out 
completely.

john zeller
cincinnati




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Date: Wed, 19 Jan 2011 10:54:32 -0500
From: "Spencer W. Thomas" <hbd at spencerwthomas.com>
Subject: Bulging kegs?

My guess is that, indeed, fermentation had not finished when you kegged. 
I don't believe that residual CO2 would provide enough pressure to bulge 
your kegs.

How can you test for complete fermentation? The simplest test is a 
"forced fermentation" test. Fill a beer bottle about 3/4 with your 
pitched wort, fit an airlock (or just cover the top with foil), and 
place it in a warm location (80F-ish), such as above the refrigerator.  
Within a few days, your wort should ferment to completion. It might not 
taste very good, but that's not the point.  Degas it, and measure the 
specific gravity. Compare to the beer in your fermenter. If it's more 
than 0.002 different, you're not done fermenting. If it's over 0.004 
different, you risk "bottle bombs" or bulging kegs.

0.004 SG is 1 degree Balling, or 1% by weight sugar, thus 10 grams of 
sugar per liter. 10 grams of sugar produces about 5 grams of CO2 when 
fermented. 5 grams of CO2 is about 2.5 liters at room temperature and 
atmospheric pressure. Compressing that 2.5 liters into the 1 liter of 
beer gives you 2.5 "volumes" of extra carbonation. I used the 
carbonation calculator at hbd.org 
(http://hbd.org/cgi-bin/recipator/recipator/carbonation.html) to find 
the pressure that 2.5 "volumes" of CO2 produces at various temperatures:

35F - 10PSI
45F - 15PSI
55F - 20PSI
60F - 23PSI
65F - 26PSI
70F - 29PSI

If you've already carbonated your beer to 2.5 "volumes", then the 
additional 2.5 "volumes" will give these pressures:

35F - 34PSI
45F - 44PSI
55F - 53PSI
60F - 58PSI
65F - 63PSI
70F - 69PSI

You're getting into bulging and bottle bomb range there.

=Spencer in Ann Arbor




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Date: Wed, 19 Jan 2011 12:46:16 -0800 (PST)
From: Calvin Perilloux <calvinperilloux at yahoo.com>
Subject: Re: Over-Carbonation? Fermentation Re-Start?

Trish,

I'm curious, what kind of kegs are you using where you have
bulging kegs and raised bungs?  That's really not good at all
with any of the kegs I've dealt with.  Have you checked the 
actual pressure using a gauge?  Might even be dangerous.

In any case, a key detail is in your statement:

>> the bungs were raised on every keg for the batch we made
>> AFTER that (Belgian Honey Ale, pitched and kegged in December)

This would indicate to me, assuming you are consistent with
your priming sugar additions before and after, that you have
a wild yeast infection in your bottling/kegging equipment.
Yes, it is possible that the yeast stalled for a while just 
as you kegged it, but seems unlikely with multiple batches, 
and I assume this FG was similar to the other O'Fests's FG.

Some wild yeasts can eat up a lot more sugars and dextrins 
in the beer than normal ale or lager yeast does, and it is 
common for homebrewers with problematic batches to have lots 
of carbonation problems and gushing.  Interestingly (though 
logically), the beer is often crystal clear.  You will
often, though, find phenolic notes in the beer, sometimes
strong and sometimes less so; this is because wild yeast
generally will not have the same "clean" character as
typical brewing yeast.

To remedy some of the carbonation problem in existing beer:

(1) Can you release pressure on the keg for now?  I have no
idea what you mean about releasing the bottom seal on the keg
(bottom seal washer on a Sanke outlet?), but what you might 
do is hook up a tap and pull off several pints, as well as 
release most of the top pressure via the tap's pressure 
relief.  Then remove the tap -- I'm assuming a Sanke --
and the keg is less pressurized and still has no air
in there.  Do this a few times over a week, and you can 
reduce the interior pressure just a bit.

(2) Put those kegs in the cooler at 32 F now!  If you have
wild yeast in there, chilling them to near freezing will 
at least reduce further carbonation activity.  Alternatively,
you might consider adding sorbate or a similar preservative
to the beer, though most people balk at that solution.

For future brews:

(1) Should you even use priming sugar?  If it were me, 
and it were beer for a festival and needed to be transported,
I'd say no, not unless there was a reason you want the beer
to be on the yeast (e.g. Real Ale).  Forced carbonation is
more controllable and leaves less sediment.

(2) - Is priming sugar the likely cause for the pressure?
No, see my above explanations.  You probably need to strip 
down whatever equipment you are using and sanitize it thoroughly.
I'd replace most or all plastic parts.  What sanitizer are 
you using?  (Just use a good one.)  Heat treat things
that you can't get into easily.  

Calvin Perilloux
Middletown, Maryland, USA



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