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Tom wrote:

Wayne, could you detail out some good fine tuning of the yeast method so
that more folks could get more out it? I'd like to see this focus used
and better for folks. Making this a less painful chore would help many
folks. It's something that's easy and cheap to play with also.
Tom Barr

I reply with a long explaination of why everyone should do it my way:

If not interested in the explaination just jump to the secoond to last
paragraph. :-)

The CO2 production has a natural tendency to peak early and as the
alchohol concentration increases the CO2 production falls off. This is
fairly useless for our purposes. We either get too much CO2 and have to
waste it or the CO2 production falls off and and we don't have enough.
The other main problem with yeast CO2 is that we normally use a nutrient
poor solution of sugar and water to start the fermentation. This means
that the fermentation will fail prematurely if nutrients are not added
at some point before the yeast loses all viability and give up the
ghost. If you add yeast nutrient or even just lots of yeast at the
beginning of the fermentation you can solve this problem but then you
have the first problem in spades of uneven CO2 production .

The solution is to use a type of yeast that tolerates low nutrient musts
and high alchohol levels. Two yeasts that will do this are Lalvin S.
Cerevisiae K1V-1116 or Lalvin S. Bayanus EC-1118. Not all Cerevisiaes
are the same so the strain number is importatant. The Cerevisiae
produces a more even fermentation but the Bayanus produces a more
complete fermentation and less yeast is required. Other yeasts will
definately work but most yeasts will not. Probably any yeast for
producing mead or champagne or any yeast that is used for restarting a
stuck fermentation will work but there is no guarentee of that.

Initially, just add a small amount of yeast to your water and sugar and
then as the yeast starts to die from higher alchohol and low nutrient
conditions add a little more yeast. The fermentation will perk up and
start to produce a little more CO2 than the initial fermentation. You
can do this for about a month and then adding more yeast will have
little effect but the fermentation will continue to for about another
month. This depends in part on the size of your fermentors. Each
fermentor should be about 1% of the size of your tank.

For best results it is best to use two fermentors. I add baking soda to
the initial fermentation to slow down the initial production of CO2. The
baking soda may not always be necessary if you start with small enough
amounts of yeast. As the fermentation progresses I tweak it by adding
more yeast so that production peaks at the end of the month.  This way I
can start my fermentations exactly one month apart. The production from
both fermentors adds together to produce a fairly flat CO2 production.
It is in fact amazing how consistant the CO2 production remains provided
the temperature is constant.

This all sounds complicated but it really does reduce the work involved
a great deal. For each aquarium I must mix up a new batch only once a
month. I then have to add more yeast twice a month. Adding yeast is very
little work but one thing to watch out for when you add yeast to an
existing fermentation is a significant amount of CO2 will gas off. I
have to leave the stopper out of the fermentor for about 20 minutes so
CO2 levels in the tank don't climb to suddenly.

Now for the details. Both my tanks are quite large. One is 120 gallons
and the other is 90 gallons. So, I use two one gallon gas cans for
fermentors. (An idea I got from this list BTW) I bought two rubber
stoppers that fit nicely in the gas can and I labelled one stopper
"even" and one stopper "odd". Using glass tubing as connectors to the
rubber stoppers I ran individual CO2 lines from the gas can to homemade
bubble counters and then to the intake of the powerhead in my aqurium.
The bubble counters contain a hagen backcheck valves. On odd months I
empty out and wash the "odd" gas can. I fill it with 2 1/2 tsps. baking
soda then 4 cups of sugar and then water to make 1 gallon of stuff. I
check the temperature of the water and try and get it around 100 degress
F. I sprinkle 1/2 tsp. of K1V-1116 yeast on the surface of the water in
the gas can and wait 20 minutes, then shake up the solution and attach
it to the aquarium by plugging in the rubber stopper. On the 12th of the
month I add a 1/2 tsp. of yeast and on the 25th I add another one. When
I add the extra yeast I leave the stopper off for 20 minutes so that the
excess CO2 will gas off. On even months I do the same thing with the
"even" bottle. It takes about 1 hour of easy effort a month.

If you change anything from this recipe you can expect changes in your
results but once you understand what you are doing it is pretty easy to
taylor a recipe for your own needs. Larger tanks need larger fermentors
and smaller tanks need smaller fermentors. Very small tanks should use
only one fermentor, very small amounts of a slow starting yeast and lots
of baking soda. Very big tanks just need very big fermentors. The amount
of yeast to add is something that can only be figured out through
experimentation. It varies according to the strain of yeast and and the
CO2 requirements. It is a good idea to make a bubble counter for each
fermentor so that you can see how to tweak your own recipe. It is better
to add too little yeast as you can always add more later. Once the exact
recipe is figured out the bubble counter doesn't help so much as there
is no way to control the CO2 output once the a fermentation is started.