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Re: Yeast fermentation (was APD V3 #1109

-----Original Message-----

>Date: Wed, 23 Jun 1999 15:18:31 +0000
>From: George Slusarczuk <yurko at warwick_net>

>Yeast ferments sugars in the ABSENCE of air -- therefore, in wine
>fermentation, one uses an "air-lock".

Actually, fermentation (of sugar into alcohol by yeast) requires oxygen.
When you fill a carboy with grape juice to make wine you leave a space at
the top to allow for gas exchange. Many [home] brewers think that this is
just to prevent foam from pushing up through the airlock but that's just
secondary to the primary purpose of providing oxygen to the yeast.

The airlock's purpose is to prevent bacteria or other organisms from getting
into the brew and spoiling it. There may be a few undesirable organisms in
there when you start a brew but generally they will be overwhelmed by the
vast quantity of yeast that you add. If you left it open while fermenting
there would be lots of dust/particles settling into the mixture any of which
could introduce undesirables.

As for this airstone idea, it's interesting but it also increases the chance
of introducing some organism that will either produce noxious gases or kill
your yeast cutting short your co2 production.


>> Date: Wed, 23 Jun 1999 16:09:54 -0700
>> From: "Bev" <bevgreen at cygnus_uwa.edu.au>

>> What would happen if one ran an air stone into a bottle of yeast + water
>> sugar (sealed) and then ran the exhaust into the aqaurium, Would this air
>> be enriched with CO2 and then bubbled into the aqaurium instead of normal
>> air (the effect would be better then straight air butnot as good as pure
>> cos - a comfortable medium.
>> I take it the sugar would not ferment anearobicaly but is it possible for
>> it to use O2 and liberate CO2, I haven't done carbon/organic chemistry