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Some thoughts on CO2 generators

I recently began trying to find a way to make a simple yeast/sugar CO2
generator last longer without maintenance.  Since many people seem to be
using this kind of setup, and lots more will be doing so in the future, it
seems like it would be a good idea to come with an improved CO2 generator
for those of us who are too cheap, and/or lazy, to go with a bottled gas

These are some of my preliminary thoughts and findings:

(All quoted material is from "The Yeast Booklet",  
http://www.diamondv.com/pdf/yeast_booklet.pdf (472k)).

"Candida utilis ... is the yeast known as "torula Yeast".  This yeast is
important because it can utilize the pentose sugars from processed wood
pulp used in making paper."

Does this mean that paper products can be fermented?  It seems like it
would take longer for wood pulp to ferment than it takes for sucrose - and
if it does, and if it could produce enough CO2 to be useful, then maybe
it's possible to make a cheap, maintenance-reduced co2 generator.  Does
anyone out there know where to find torula yeast?

"Yeasts are 'facultative anaerobes' which means that they can survive and
grow with or without oxygen.  Yeast propagation is an aerobic processes
[sic] where the yeast converts oxygen and sugar, through oxidative
metabolism, into carbon dioxide and usable free energy for efficient yeast
cell growth.  However, the production of alcoholic beverages ... and
industrial alcohol are anaerobic processes.  Anaerobic fermentation is much
less efficient, resulting in considerable 'metabolic by product' in the
form of ethyl alcohol.  
The yeast ferments simple sugars into ethanol and carbon dioxide and the
yeast grows very slowly.  To optimize ethanol production,  the fermentation
process is carried out without oxygen being present; but, to maximize yeast
cell growth, an abundance of oxygen is provided in the form of air."

A table at the end of the previous paragraph shows: 
Aerobic Growth:  
	1 glucose + 6O2 = 6CO2 + 6 H2O;   686 Kcal free energy
Anaerobic Fermentation:
	1 glucose  =  2CO2 + 2 ethanol;        54 Kcal free energy

So it would seem that if one could provide 6 O2 per each glucose
metabolized, CO2 would be generated without the toxic alcohol as a
by-product.  Doing so would probably present these difficulties:

1)  The lifespan of the CO2 generator would be shortened, since the sugar
would be 
      metabolized more rapidly (I think...);
2)  O2 would need to be dissolved into the yeast/sugar solution on a
continual basis;
3)  O2 that escapes from solution will be present in the CO2 reactor, which
     make it necessary to devise a reactor efficient enough to dissolve all
of the gasses 
     that escape from the generator, in order to be sure that the CO2 isn't
bubbling out 
     with the excess oxygen;
4)  Chemistry problems make my brain hurt.

(I haven't yet thought of a practical way to implement an aerobic
generator; for now, my plan is to present the information and hope that
someone else can think of something.)

Metabolites - by-products of the fermentation of sugars - can include
"peptides, alcohols, esters and organic acids", depending on "the
composition of the media fermented and the conditions of the fermentation

If a yeast-bottle generator could produce metabolites that are either less
toxic to the yeast, or more easily removed from the solution, than alcohol,
then it might be possible to have a longer-lived generator.  Since (AFAIK)
brewers and those other folk are after metabolites other than CO2, there
doesn't seem to be any long-established scheme for optimizing CO2
production; and if there is, I would guess that the emphasis is on the
quantity produced, rather than on the duration of the process.  Therefore:
adopting a known practice (fermenting sugar in water) may not yield the
results we really want (i.e., a CO2 generator that thrives on neglect.)

It could be, of course, that the yeast-bottle method is as good as it gets.
 It that's the case, maybe we can fine-tune it by using different sugars
(rock sugar, brown sugar, corn syrup, ...) and different yeasts, by adding
specific nutrients, by finding a simple way to remove alcohol from the
solution, by either adding or reducing the chlorines in the water, or by
making some other simple change to the standard methods.  What do you
think?  Does anyone know a yeast researcher?  

- Ted Hamiter
thamiter at jps_net
In sunny ol' Crockett, CA