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DIY CO2 Production and Sanitation

Recently, a listmember related an experience where the
contents of his fermenter were siphoned into the tank,
fouling the water and creating a smelly mess.

The first rule of making beer and wine at home is
'sanitation, sanitation, sanitation.'  Remember that a
food source for microbes (sugar) will be held in a
concentrated aquaeous solution for a period of days to
weeks at room temperature.  Bacteria and wild yeasts
could not ask for better conditions.  These organisms
cannot be completely eliminated, but conditions can be
created that favor the propagation and development of
a monospecific culture of desirable yeast.  

The aquarist should be at least as concerned as the
brewer/winemaker when it comes to sanitation.  A
homebrewer with infected beer pours out $25 to $40
worth of ingredients.  An aquarist with an infected
tank may pour out hundreds of dollars in fish and
plants and wipe out years worth of work.  Poor
sanitation in a DIY CO2 generator can lead to pressure
and temperature differences between the fermenter and
the tank.  That's all it takes to create a siphon and
introduce the contents of one vessel into the other. 

Most bacteria cannot survive a period of boiling
temperatures.  So the first defense against invasion
is to boil your solution of sugar and water for at
least 15 minutes.  As the solution cools, it passes
through a temperature range that is ideal for the
propagation of bacteria.  Rapid cooling of the
solution decreases the risk of invasion.  The easiest
way to cool the solution rapidly is to cover the pot
when as the heat is turned off (sanitizing the lid),
and place the pot in an icewater bath.  

The fermenting vessel needs to be clean and sanitary
also.  If there is any gunk or dirt on the bottom,
sides or cap, it must be removed or the fermenter
replaced.  No exceptions.  If it ain't clean, it can't
be sanitized and it should not be used.  The inside of
the bottle should also be free of any gouges or
scratches.   After it has been cleaned and inspected
for scratches, it can be filled with a solution of 1
teaspoon bleach per gallon of water.  Allow it to sit
for 15 minutes, and rinse with hot water.

Any other equipment or materials that come in contact
with the solution of sugar and water should be clean
and at least rinsed with hot tapwater before being
used.  That includes the cap for the bottle and the
airline tubing.

The yeast should be dissolved in a cup of pre-boiled
warm water prior to adding it to your bottle.  If not,
the osmotic pressure caused by adding dormant, dry
yeast to a concentrated sugar solution will kill in 
large numbers.  This forces the yeast to use nutrients
and Oxygen to regrow their population.  When the
hydrated yeast is added to the sugar solution, the
mixture should be shaken vigorously for several
minutes.  This introduces Oxygen and promotes rapid
propagation of the culture.

The temperatures of the yeast bottle and the tank it
will be used on should be the same or close.  If your
yeast culture is warmer than the tank water, tank
water will be sucked through the tubing and could
enter the bottle.  That's usually only a minor
nuisance.  If the tank water is warmer, the reverse
could occur.  This may collapse thin-walled plastic
bottles and force the yeast into the tank.  That's
usually a disaster.

The safest place for the fermenting solution is below
the aquarium.  If something happens and a siphon is
created, you want the tank water to go into the
bottle, NOT vice versa.  If your bottle is sealed
properly and there is a good, strong connection
between the tubing and the bottle cap, it will hold up
under the pressure caused by the head differential. 
If your bottle is above the aquarium and its walls
collapse, the entire contents of the fermenter will go
into the tank.  

Your tank's water is nutrient and Oxygen rich.  When
healthy yeast are introduced into that environment,
they respond by propagating wildly.  Within 30
minutes, the yeast are capable of depleting all
dissolved Oxygen and raising their population levels
into the millions of cells per liter.  Ethyl alcohol,
the yeasts' most desirable by-product in beverage
making can kill your biofilter.  The aquarist is
trained to respond to such crises with massive water
changes.  The yeast respond to a reduced cell count
and brand new, Oxygen-rich water by multiplying again.
 If the aquarist continues to do massive water
changes, then the aquarist has merely converted the
tank into a yeast production machine.

I have not been keeping planted tanks long enough to
state what might get a yeast-infested tank cleared up.
 However, salt, potassium permanganate and medications
designed for treating fungus and bacterial infections
should produce some results.  Charcoal and fine
mechanical filtration should also help remove the
dead/dying yeast.  I believe that if you're careful
about how you build your system and pay attention to
maintaining sanitary conditions, you'll never have to
deal with yeast in the tank.

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