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	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 --


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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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