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HOMEBREW Digest #4849
HOMEBREW Digest #4849 Fri 16 September 2005
FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
Digest Janitor: pbabcock at hbd.org
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Contents:
Pathways & philosophy (was: Esters) ("Fredrik")
Warming/airing your hops before use ("Fred L. Johnson")
Re: searching the HBD (Dean)
Using oats in light-coloured beer ("Greg 'groggy' Lehey")
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Date: Fri, 16 Sep 2005 08:10:03 +0200
From: "Fredrik" <carlsbergerensis at hotmail.com>
Subject: Pathways & philosophy (was: Esters)
> Most texts just point to the pyruvate and the pyruvate dehydrogenase which
> together with a CoASH directly produce acetylCoA (actually it's a 3 enzyme,
> 3 step process). We know that doesn't happen in anaerobic yeast based on
> recent studies, the enzyme is absent. It appears that all the acetylCoA
> comes from pyruate -> acetaldehyde -> acetate (the acetic acid anion) ->
> acetylCoA, but most books supply few details.
Thanks for pointing this out Steve! I find this to be a quite important point.
It's true that many books something are fuzzy on this. I've been
confused about this too. I looked up the ASC enzymes at that point, but
wasn't cafeul enough to realize there is not one, but two. The first one is not
relevant in fermentation, but the second one is.
(I should point out that in a previous post I did with a crude
respiration/fermentation switch estimate, I didn't actually account for the
acetate route to acetyl-CoA, I should have. )
The sources I have I and just rechecked says that during glucose limited
respiration the mitocondrial (PDH) puryvate -> acetyl-CoA is the
dominating pathway. But as the glycolytic rates increases the cytosolic
(ACS2) acetate -> acetyl-CoA route is alerted, and dominates in
fermentation. But even during during glucose limited aerobic considtions
the (ACS1) acetate -> acetyl-CoA route takes care of acetate to
regenerate acetyl-CoA.
I found this before, but didn't pay attention to the fact that there were
TWO ACS genes, ACS1 and ACS2. ASC1, is only expressed as it seems during
aerobic conditions. So if you stop reading there, you'll reach wrong
conclusions :)
But when I lookd again, I now found that ASC2 is indeed expressed
and even critical for fermentative growth.
There is an interesting free paper available online
The Two Acetyl-coenzyme A Synthetases of Saccharomyces
cerevisiae Differ with Respect to Kinetic Properties and
Transcriptional Regulation*
http://www.jbc.org/cgi/reprint/271/46/28953
that shows that yeasts lacking the (ACS2) acetate -> acetyl-CoA even
fail to
grow on oxygen limited glucose. So the pathway isn't only possible, it's
mandatory.
- ----------
Som yeast philosophy talk
I am fascinated by the fact that yeast regulations have
much of seemingly coordination of regulations. One expressed gene
may stimulation expression of others and at first through this seems
to just make things even complicated.
But on second thought, I wonder if it's not a simplification after all,
if you only look at it the right way? Even a cell, has limiting
processing power, why not remove redundant controls and
coregulate when possible? That seems sensible.
I read an article in Yeast 2000;16:1287-1298 that points to some
possible correlations between membrane fluidity, and AAT synthesis
since both oxygen and UFA has been suggested to repress the ATF1
at transcriptional level, but by independent mechanisms. Instead of
waiting for the membranes to improve, perhaps yeast has learned that
once oxygen appears, it's usually only a matter of time, until the
will improve, so the might as well use that for triggering and be
ahead of things? If I was a yeast cell, I'd probably keep trying
to find clever ways find shortcuts in the signal system and make
the regulation taks more compact, since even a cell has limiting
"computing power"? Obviusly triggering on O2 will give a more early
signal, and allow for faster responses that would waiting for the
O2 to get incorporated into lipids and put into the cell membrane.
/Fredrik
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Date: Fri, 16 Sep 2005 08:54:37 -0400
From: "Fred L. Johnson" <FLJohnson at portbridge.com>
Subject: Warming/airing your hops before use
I recently heard in a podcast on basicbrewingradio.com featuring an interview
with Gerard Lemmens that it is important to bring hops out of the freezer 24
hours prior to using them to allow them to loose certain aromatics that can
impart off flavors to the beer.
- --
Fred L Johnson
Apex, North Carolina, USA
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Date: Fri, 16 Sep 2005 09:44:48 -0700
From: Dean <hbd at deanandadie.net>
Subject: Re: searching the HBD
I use google directly to search the HBD (like the google search on the HBD
search-page). The trick is to use some of google's special keys. I always use
the following in my searches:
site:hbd.org inurl:archive
That limits google to all web pages on a hbd.org server with the string
"archive" in the URL. In other words, just the hbd archive.
Searching the HBD is tricky because of the digest format - there's a lot of
diverse information in each issue. For example if I want information about a
cooler-type mash tun, I could get digests with information about jockey boxes
and keg-type mash tuns instead of what I want.
If the janitors are listening to this message, I have a solution to
inconsistent searches. It does not take much effort on their part. If each
individual message was split out from the digest and given it's own page then
information would be separated from other otherwise unrelated information.
Then if the janitors put the messages in a different directory (such as
/archive/messages) then we could use the aforementioned google trick to search
discrete package of information.
This would, of course, double the space required for the HBD, and I do not know
how big the server is. There is also the problem of the effort. I volunteer
my time to write a splitting script.
Regards,
- --Dean - Unscrambler of eggs
- --
Take your time, take your chances
[3278.7 km, 273.4] Apparent Rennerian
- ------------------------------------------------------------------------------
It matters not how strait the gate / How charged with punishment the scroll
I am the master of my fate / I am the captain of my soul. -- Invictus --
-- William E Henley --
------------------------------
Date: Sat, 17 Sep 2005 11:11:15 +0930
From: "Greg 'groggy' Lehey" <grog at lemis.com>
Subject: Using oats in light-coloured beer
I'm thinking of experimenting with a bit of oatmeal in a
light-coloured ale. I've never used oats before, but I gather this
isn't the way they're usually used, so before I go and do something
silly, I'd be interested in feedback on whether it's a good idea or
not, and what pitfalls there may be.
Questions I have are:
- The main intention is to improve the head; I've been finding that
the lighter the colour of ale, the less the head. So: are oats
going to help here?
- I'm planning to use commercial oat flakes intended for porridge. Is
this a good idea? If not, what should I be looking at?
- What difference do oats make to the colour? I'm guessing that since
it's not roasted, it'll make very little difference.
- How much should I be trying to use? I'm guessing 10<insert percent
sign here> of the total weight of the grain, but maybe 20<insert
percent sign here> would be a better choice.
- I typically use a two-step infusion mash (63<insert degree sign
here>/72<insert degree sign here>). Am I going to glue up my mash
with porridge?
Sorry for the <insert here>s. The mailing list rejects the correct
symbols.
Greg
- --
Finger grog at lemis.com for PGP public key.
See complete headers for address and phone numbers.
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End of HOMEBREW Digest #4849, 09/16/05
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