HOMEBREW Digest #4849 Fri 16 September 2005

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  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 Return to table of contents
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 Return to table of contents
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 -- Return to table of contents
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. Return to table of contents
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