[email]Daffaed@gmail.com[/email] <Daffaed@gmail.com> wrote:[color=blue]
>While there are many factors which can inhibit yeast activity: alcohol
>content, lack of nutrients, lack of oxygen, pressure as well as
>others, at bottling time in beers, it seems that all but the oxygen
>requirment are present. Beers don't generally have adequate alcohol,
>there's plenty of nutrients left, and at bottling time, pressure is
>essentially ambient. Only oxygen is left.[/color]
[color=blue]
>Well, chemistry tells us that there needs to be an adequate supply of
>oxygen for CO2 production.[/color]

Yes.
[color=blue]
>After fermentation, the beer has little
>available dissolved oxygen left...[/color]

Dissolved oxygen is not what's needed. While free oxygen
certainly helps yeast multiply, it isn't necessary for production
of CO2.
[color=blue]
>Some oxygen is made
>avialable from the digestion of the priming sugar itself. Fructose
>and glucose for instance have six carbon atoms and six oxygen atoms
>Maltose and sucrose each have 12 carbons and only 11 oxygens. The
>problem is that carbonation uses oxygen at twice the rate of carbon
>(ie cabron DI-oxide) so there has to be at least some residual oxygen
>available for use in CO2 production.[/color]

It's not exactly a question of oxygen availability. You
got the first part right, but yeast absolutely doesn't need
free O2, they only have to break the bonds in the sugars
to produce CO2 and ethanol.
[color=blue]
>As a test, I tried with a recent batch of beer taken from the
>secondary and most of it was carbonated as usual. A small portion of
>it though, I aerated with an oxygen cylinder and stone to introduce
>dissolved oxygen into the beer.(Don't get on me about the addition of
>oxygen to the beer at this time, it was a test of a theory) Then I
>added priming sugar and filled five bottles to the top. Capping
>actually squeezed a little beer out of each bottle so I know they were
>full. Within a week and a half, three of the bottles had either
>ruptured or blown thier tops and I took the remaining two outside to
>pop them before my wife tried to kill me for making the basement smell
>like an old frat house. It tasted pretty poor, but the carbonatioin
>was excellent (over-carbonated actaully). This leads me to conclude
>that an adequate headspace must be left as a reservoir of oxygen for
>the yeast to use for carbonation.[/color]

I'm not convinced your conclusion is the only possible
one based on the evidence.
--
Joel Plutchak "They're not people, they're HIPPIES!"
$LASTNAME at VERYWARMmail.com - Eric Cartman