[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: aerated yeast and related things.

Paul Krombholz wrote:

> I wonder if it would be helpful to flush the system with air periodically
> so that the O2 supply gets renewed and the accumulated CO2 gets pumped into
> the tank.

There's a limit to how fast you can get the CO2 to dissolve in the tank.
I think flushing the reactor would exceed the limit.

Putting air into the head space over the top of the solution isn't the
same thing as aerating the solution.  If you want aerobic reactions in the
solution then once the reaction starts you have to provide a continuous
supply of oxygen that is equivalent to the CO2 supply that results
(assuming the perfect reaction - one oxygen molecule in gives one CO2
molecule out).  And that oxygen has to be mixed with the solution, not
sitting in the headspace above the solution where diffusion alone gets it
to the critters that need it.

> A one minute flush when the lights come on in the morning might be a
> good time to deliver CO2.  It should be possible to rig some kind of
> clever system so that when the pressure goes negative due to oxygen
> consumption, a switch is turned on to a small air pump to flush the
> system for a minute or a half minute.

That's an awful lot of fiddling for something that works very well as a
low-tech, DIY system.  It sounds easier to just set up a bottled CO2
system.  Even a pH-controlled bottled-gas system might be simpler than

> If the culture can be kept aerobic, the
> yeast will produce a lot more CO2 than if it goes anaerobic.  Under
> anaerobic conditions you get two molecules of CO2 and two molecules of
> ethyl alcohol from a molecule of glucose.  Under aerobic contitions, you
> get 6 molecules of CO2 (and nothing else except 6 molecules of water) from
> a molecule of glucose.

Have you actually done this?

I'm of the impression that yeast don't compete well with bacteria under
aerobic conditions and that the aerobic bacterial conversion of glucose to
6CO2 would not be a simple process and might proceed, ummm... with
difficulty.  Maybe not at all, maybe too slowly, maybe at a very irregular

Then, Susan Romano wrote:

> But first I must clarify my "exploding yeast problem" comment. I have heard
> of airstones backing up in that manner but what I meant to say was that the
> whitish slime clung to all the plants,and accessories in long trailing
> plumes. Pretty gross and smelly too. I had this problem after I tried to
> aerate the tank to kill off the bacteria the yeast might be consuming by
> adding a tsp. of 35% hydrogen peroxide(O2 and water, right?) Bad move, I
> even lost some fish.

Hydrogen peroxide isn't O2 and water.  It's a potent oxidizing
disinfectant and adding it is comparable to adding chlorine bleach.

> Seems to me it shouldn't have hurt though, but I'm not
> a card carrying chemist, that's for sure. My question to Paul Krombholz and
> other chemist types is would adding hydogen peroxide to the DIY CO2 mix,
> add oxygen to it safely? I'm a little nervous to try it after my previous
> fiasco. If so, how much would you reccommend and how often?

There's a possibility that the peroxide would react with the sugar. If it
doesn't, then it would tend to kill the yeast, and most anything else in
the reactor.

And on to other things...

As someone else pointed out, if you flush air through the reactor, what
you get out is a mixture of air and CO2 (mostly air) and you will get
precious little CO2 dissolved in the tank because the dissolution rate of
CO2 from the mixture will be much lower than the dissolution rate of
"pure" CO2 gas.  Output from a yeast reactor is fairly clean, but it isn't
quite pure.  It should be about saturated with water vapor.

There are simple precautions against getting yeast solution in the tank.
Don't use reactors that can be tipped over, or if they can be, put them
where they have some support and aren't likely to be tipped.  Use
containers with fluted sides that don't tend to collapse.  If possible,
place the container several feet below the water surface in the tank.
Don't plug the outlet from the reactor directly into a pump inlet.

Two-liter soda bottles make bad reactors because a) they are easily tipped
and b) their sides are easily collapsed.  Fruit juice and sport drink
bottles with fluted sides are more stable and less likely to collapse.  I
also use some 1-gallon jugs that are low and square that just don't tip.
In the case where I do use a soda bottle, the bottle is wedged against the
tank stand so it can't be tipped.  If you can't do something like that,
then consider banding the jug to something solid. I bet an old nylon
stocking would work very well for that.  Tape or even plastic cling wrap
would also work.

And always remember when using yeast-generated CO2 that you're dealing
with a live culture, not a spontaneous chemical reaction.  Success has
more to do with biology than it does with chemistry.

My two CO2-fertilized tanks are running very well and I've only made two
batches of sugar/yeast so far this year.  The first one ran from Jan 18
(MLK Day weekend) to March 1 (6 weeks) and was still active and sweet when
I took it down.  The current batch has been running for 8 weeks.  I'll
probably clean the reactors this weekend and start new batches.  I'm
extending their longevity by starting with relatively little yeast (1/8
teaspoon per 2-liter reactor) and getting a lower CO2 production rate. I'm
careful to keep everything clean.  The new solutions take several days to
come up to speed.

Roger Miller

In Albuquerque, where it's dry, dry, dry.