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HOMEBREW Digest #4954
HOMEBREW Digest #4954 Fri 17 February 2006
FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
Digest Janitor: pbabcock at hbd.org
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Contents:
Alpha-acetolactate ("Stevens, Jonathan C")
diacetyl production/reduction ("Fredrik")
competition announcement - 11th annual South Shore Brewoff (RI_homebrewer)
Overcarbonation (Thomas Rohner)
brewpubs in Phoenix ("Wayne Love")
Dogs eating hops (Randy Scott)
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Date: Wed, 15 Feb 2006 20:18:00 -0500
From: "Stevens, Jonathan C" <Jonathan.Stevens at dhs.gov>
Subject: Alpha-acetolactate
-S:
>I'm not sure I buy that one and would like to hear more on
it. I think the major pathway to diacetyl is when pyruvate
is converted to alpha-acetolactate on the way to amino acid
synthesis, and the alpha-acetolactate is non-enzymatically
decarboxylated to diacetyl. I can't see how fermentation
temp makes a big difference here. The acetolactate doesn't
pool because ... ??why??
I'm not sure why. Anecdotally, I know that the only ferments in which I
experience residual diacetyl, are those which were conducted entirely in
cold
environs. The warmer the ferment, the less likelihood there will be
diacetyl in
the resultant beer. Why do we temporarily warm the fermentation to perform
a
'diacetyl rest'? I think the non-enzymatic decarboxylation reaction is
dependent upon heat; the greater the temp, the more rapid the reaction.
Indeed,
the brewhouse test for alpha-acetolactate in the finished beer is to force
oxidative decarboxylation by heating a sample to 140 degrees F for 30
minutes,
cool, then taste the sample side by side with a non-heated sample. If
acetolactate is present, diacetyl will rear its ugly head (and if you've
tried
this on an acetolactate rich sample, it's almost miraculous how the beer
magically goes from perfectly drinkable to butta' before your very nose).
This
explains how we get from alpha-a to diac...from diac to amino acid synthesis
is
up to the yeast. But there again, everything in yeast metabolism occurs at
a
more rapid rate at warmer temps. So I think there may be some face validity
to
the notion that allowing the ferment to free rise to a warmer temp will
result
in a quicker 'driving off' of diacetyl.
My $0.02,
Chad Stevens
QUAFF
San Diego
P.S. We will judge America's Finest City Homebrew Competition this Friday
and
Saturday. 300+ entries from 18 states! Hope to have winners announced by
Monday. Thanks HBD'rs and Good Luck!
------------------------------
Date: Thu, 16 Feb 2006 07:46:45 +0100
From: "Fredrik" <carlsbergerensis at hotmail.com>
Subject: diacetyl production/reduction
> <<
> 4. No diacetyl. No need for a diacetyl rest because you've
> fermented in temperature ranges where the yeast are converting
> all of the precursors readily.
> >>
>
> I'm not sure I buy that one and would like to hear more on
> it. I think the major pathway to diacetyl is when pyruvate
> is converted to alpha-acetolactate on the way to amino acid
> synthesis, and the alpha-acetolactate is non-enzymatically
> decarboxylated to diacetyl. I can't see how fermentation
> temp makes a big difference here. The acetolactate doesn't
> pool because ... ??why??
Maybe I am missing the real point here but anyway...
..maybe there are multiple explanations, like the tweaked
growth profile associated with temperature change might
tweak the amino acids uptake too, and thus the timing
of diacetyl peaks, but it seems this could depending on
situation affect things in either direction. The way I
understand that part, the diacetyl production is related
to the amino acid uptake sequence and the
amino acid balance vs de novo synthesis pathways. And
as long as high preference (group A) amino sources are available
the inhouse biosynthesis of valine and leucine
stimulate acetolactate production.
I see the amino acid sequencing to be somewhat
analogous to the sugar sequencing in that prefrerred
aminos repress less preferred to a certain extent.
But set aside other more complex possibilities, they way
this is currently encoded in my head the
non-enzymatic oxidation of alpha-acetolactate
to diacetyl outside the cell is favoured by a higher temperature.
And this step seems to be the bottleneck
(which is probably why diacetyl sometimes tend to
appear again out of nowhere in keg or bottle), so the sooner
all the "potential diacetyl" (alpha-acetolactate) is converted to
free diacetyl, the sooner can it be reassimilated and reduced
by yeast to acetoin and butandiol.
/Fredrik
------------------------------
Date: Thu, 16 Feb 2006 19:09:29 -0800 (PST)
From: RI_homebrewer <ri_homebrewer at yahoo.com>
Subject: competition announcement - 11th annual South Shore Brewoff
Hi All,
This email is the announcement of the 11th annual South Shore Brewoff
hosted by the South Shore Brew Club. This year's Brewoff will be held
on Saturday, April 1st, 2006 in Mansfield, MA.
Entries will be accepted in all 28 BJCP style categories, per the
2004 BJCP style guidelines.
Complete entry and judging information is available on the South
Shore Brew Club website at http://www.southshorebrewclub.org/.
------------------------------
Date: Fri, 17 Feb 2006 16:48:34 +0100
From: Thomas Rohner <t.rohner at bluewin.ch>
Subject: Overcarbonation
Hi Keith
most of us had it at least once.
I had a carbonation monster to fight with lately. One bottle even
exploded, but luckily nobody was hurt. I then put it into our walk-in
cooler, which is set to 4 deg celsius. A week later i tried to open a
bottle. It gushed out like a fountain, leaving maybe a 5th in the
bottle. This called for harsher measures, so i put it into one of the
fermentation freezers and set it to -2 deg, after another week and
another not so successful test i set it to -5 deg. I was a little
concerned it would freeze, but since it is a 19 plato monster, it has
enough antifreezer in it. Then we decanted 90 bottles into a fermenter,
careful not to agitate it to much. I rehydrated 3 packets of champagne
yeast and put it into the fermenter. Then came one of my brew-buddies
and started to shake the fermenter vigorously. (as he would do with a
freshly pitched batch of wort) In this case it didn't really help....
2/3 of it gushed out and went down the sewer.
Well this is our worst brewing desaster in 8 years. The problem was, we
didn't take fg readings regularly. We let it ferment and "check" the
bubbling, but we ferment it for at least 2 weeks. This worked well in
over 250 batches. In this case i think the yeast was pooped out.(a
belgian high grav. yeast but after 2 low and 3 high-voltage brews it was
too much for the poor yeasties to keep going at normal pace. They did
indeed finish the sugar off, but at that time the bottles were already
closed)
The intention behind this more or less failed rescue mission was to let
it warm and degas "s l o w l y", ferment what ever fermentable was
there, then prime again and rebottle.
Most homebrewers i know around here use swingtop bottles to correct
overcarbonation problems. But most of them bottle at a point were just
enough remaining sugar is left to carbonate. (called "gruen schlauchen")
Cheers Thomas
------------------------------
Date: Fri, 17 Feb 2006 15:18:13 -0400
From: "Wayne Love" <wlove at claired.com>
Subject: brewpubs in Phoenix
I'm off to Phoenix for a week long conference at the first of April and
will have a few extra days to misbehave and was wondering if anyone can
suggest some good brew pubs to visit or some local beers not to miss.
Feel free to send responses off list.
Much appreciated.
Wayne Love,
Rothesay, NB, Canada
------------------------------
Date: Fri, 17 Feb 2006 14:57:15 -0600
From: Randy Scott <lists at rscott.us>
Subject: Dogs eating hops
I'm rather behind on my HBD reading and just got to the discussion a
couple weeks ago about hops being toxic to dogs, and whether they'd eat
raw plants. I never knew about the toxicity, and was alarmed to hear
of it because one of my German Shepherds ate the better part of a 20-ft
plant last summer (with no apparent ill effects, thankfully).
I did a bit of Google research, and apparently hops toxicity is related
to something called Malignant Hyperthermia, which in turn is linked to a
specific genetic trait. If I'm understanding it right (no guarantee of
that - I Am Not A Veterinarian) it would only be a problem if your dog
has a specific genetic marker, which seems to be relatively common in
Greyhounds and to a lesser extent Retrievers, but not so much in other
breeds.
Anyway, there's at least one known instance of a dog consuming a live
hops plant (which is not to say that dogs are particularly attracted to
them; my dog was then a puppy and ate pretty much everything in the back
yard that wasn't made of wrought iron) and it seems this could be quite
dangerous to some dogs. I think if I kept Greyhounds or Retrievers (or
mixes thereof) with propensities for chewing, I'd not grow hops, just in
case.
For more info, Google : "malignant hyperthermia" dogs hops
ras
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End of HOMEBREW Digest #4954, 02/17/06
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