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Contents:
  haze/bottle condit/mixed yeasts (steve alexander)


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Date: Sat, 20 Sep 2008 12:46:10 -0400
From: steve alexander <steve-alexander at roadrunner.com>
Subject: haze/bottle condit/mixed yeasts

Thanks to Ed Case resurrecting a link to Gillian G's encyclopedic notes 
on haze (mostly appears in MABS IIRC).  I think that  what is lacking 
there is insight.   Protein/phenolic haze is most certainly the primary 
issue in normal brewing with decent technique & sanitation.   There is 
no simple more=better or less=better relationship wrt to phenolics; It's 
a rather complex topic.  Too little tannoid phenolic may allow a protein 
haze to persist, or added phenolic may create a protein-phenolic complex 
haze.    Probably the surest way to avoid haze is to proteolyze the heck 
out of the proteins, but this leads to insipid low body beers than may 
also lack head.  PVPP will certainly reduce the level of tannoid 
phenolics with little or no negative impact, but it may not help after 
haze has formed.

As usual it's a balancing act and so the goal it to just barely 
proteolyze enough to avoid an offensive haze, yet leave body.


Ed Case also notes ...

> > In John Palmer's "How to brew" (3ed) p92 he says 
> > that there have been several studies that have shown 
> > that yeast only consume 30% of the oxygen in the
> > headspace of the bottle.
> >
> > Received wisdom in the UK is that the yeast 
> > consumes effectively all of the yeast, so I was 
> > wondering if anyone has references for
> > any of the studies or better still copies?
> >   
>   
I wasn't aware of that figure, but it must be taken with a grain of 
salt.  The amt of O2 consumed by yeast is likely to be very dependent on 
the yeast amount and condition, and any remaining O2 will likely be used 
up in short order by (flavor negative) oxidation processes  (O2 reacting 
with beer constituents), but those oxidation processes are inhibited and 
some even reversed by the normal anaerobic yeast metabolism.

In any case it's clear (IMO) that  bottle conditioned  beers remain 
fresher and more flavorful  for longer periods than beer handled in 
other ways.   Even the hop flavor & bitterness persist better.  Too bad 
it's such a PITA to bottle.

Scanning John Palmer's book references and my bookshelf I see this 
figure came from George Fix's "Analysis of Brewing Techniques", pp 
136.   Fix includes the dubious statement, "... only 30% of the AIR of 
the headspace was consumed in bottle refernetation, and the remaining 
70% was ultimately absorbed into the beer" [my emphasis].  Of course 
this comment makes little sense unless we GUESS that Fix meant OXYGEN 
and not "AIR".  Fix does include two references.
Eric Warner 1992 - "German Wheat Beer"
Derdelinckx, G., B. Vanderhasselt, M. Madoux, K.P. Dufour 1992, 
Brauwelt, vol 2.
The latter seems to be "Refermentation in bottles and kegs: a rigorous 
approach", but I have no access.  Warner's book merely talks vaguely 
about bottle conditioning wheat beers, and suggests not worrying abt 
headspace air, but also not exposing the beer to excessive oxygen.

In another more recent paper by some of the Brauwelt article authors ...
https://lirias.kuleuven.be/bitstream/123456789/163378/1/
2008-Beer&Health+Elsevier+CH004.pdf
they state, "Beer protection against dissolved oxygen is often mentioned 
as another advantage of refermentation.  This is certainly true when 
bottling occurs with obsolete machines".  A 30% reduction in O2 doesn't 
sound very protective to me, so I have some doubts about Fix' 
interpretation.  They also refers to this article:
http://www.mbaa.com/techquarterly/abstracts/1997/tq97ab20.htm
where the abstract suggest the speise inclusion uptakes "some" of the 
oxygen.  No other authoritative source immediately available to me gives 
a figure.

Darrell asks -

> > I recently mixed several yeasts, in that they were all old and I thought I
> > would maximize the chance that something would wake up.  One was a 2 year
> > old Wyeast German Ale, one was a 2 year old Wyeast Ringwood, and the third
> > was also several years old, but a dry Safale 25.
> >
> > The result was interesting.  And, each time I re-use it , I think that I
> > get more of the "ringwood" flavor (some of that diacetyl).  Do you guys
> > ever mix yeasts?  And, then re-use?
> >   
>   
I think you've explained why this is rarely done.   Under anyspecific 
fermentation conditions one yeast will perform better and  eventually 
dominate.  If you want to form a stable mix of flavors you'd need to 
ferment separately and blend.  OTOH it sounds like a fun experiment if 
you don't care too much about the result.

 -S




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