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Re: DIY yeast CO2

On Sat, 21 Oct 2000, Erik wrote:

> I have read back posts on the Mailing list and every one says to use; 1 cup 
> sugar, 1 tsp. yeast, and 1 tsp. backing soda.

Baking soda is optional.  There are several variations on the recipe.

I use 1 1/2 cups of sugar for a 1/2 gallon container and fill the
container up to about 1 inch below the outlet.  I've varied the amount of
sugar up and down a little and I don't seem much difference.

You can also vary the amount of yeast and the type of yeast.  I use
baker's yeast at about 1/4 teaspoon per 1/2 gallon container.  I have
experimented with amounts varying from a fourth to 4 times that much
yeast.  With more yeast I get a quicker start and with less yeast I get a
slower start.  Using a very small amount of yeast reduces the amount of
CO2 I get, but the other proportions all seem to produce about the same
amount for about the same amount of time.  I don't use yeast nutrients
because it's so easy to just start a new batch when it slows down, or a
larger batch if you need more.

> My question is, i have 3 liter bottles. Is that OK? I don't see much
> of a difference that it would make.

Yes.  You can use any size bottle you want.  Just adjust the recipe to
match.  Lot's of people report problems with soda bottles tipping over or
collapsing under suction, so I advise you to avoid them.  Gatorade bottles
are good, and lots of products are sold in similar rigid, tightly sealing
bottles.  I use 1-quart bottles for 10-gallon tanks, half-gallon bottles
for 20 gallon tanks and 1-gallon bottles for my 55 gallon tank.

I double the recipe for the one gallon bottle.  For the 1-quart bottles I
make enough of the mix for 1/2 gallon bottle and split that between two
1-quart bottles.

To make the solution I start with a scant 1 quart of water (quart and a
half for a one gallon bottle), put that in a sauce pan, add sugar and
bring it to a boil.  After it reaches a rolling boil I take it off the
heat and add ice cubes to bring the temperature down to a point where I
don't think it will hurt the plastic bottle.  Then I pour the solution
into the bottle and fill the bottle the rest of the way with tap water.  

I aerate the solution in the bottle with an old air pump. I add the yeast
after the solution has aerated for a while but while the solution is still
warm to the touch.  I continue aerating until the yeast is fully
dissolved. After the yeast is fully dissolved I seal the bottle and set it
aside. The mix starts producing useful amounts of CO2 in 2-3 hours.  
*Don't* connect the bottle to your CO2 line until after it reaches room
temperature, otherwise the cooling air in the bottle can create a suction
and draw aquarium water down into the sugar solution. That can culture
bacteria in the sugar solution, kill the yeast and create an awful mess.

With this method it takes about an hour to make up the solution for 5

> Also, how long does it last? I used 2 cups of sugar before and it stoped 
> after a week.

I change mine once a month, but I have had useful output for up to six

Output peaks soon after the new solution is mixed and declines afterwords.
The yeast settles after two or three weeks and the solution becomes mostly
clear (sometimes pinkish).  CO2 production continues for some time after
that, but after a while it just isn't enough to do any good.  It's your
call when to replace the solution.

When people report their mix lasting only a week or so the problem is
often caused by a leak.  Usually this is around the lid or at the point
where the outlet passes through the lid or the bottle.

The yeast CO2 system is very forgiving about the exact recipe, the type or
size of bottle and a lot of other variations.  The one thing you can't get
away with is a leaky bottle.

To reduce the chance of leaks, use tightly sealing lids, make sure the
seals in the lid are in place and screw the lids down firmly.  In the case
of Gatorade bottles, don't mix-and-match lids and bottles; they use
several different kinds of lids and bottles and the lid from one bottle -
even though it might look like it's the same size as the lid from another
bottle - may not seal on a different bottle.

Also, you're probably better off putting the CO2 outlet on the shoulder of
the bottle below its top instead of through the lid.  That leaves the lid
seals in place.  Also it avoids twisting at the connection every time you
take the lid off the bottle.

I make the outlet from a short (1 1/2 inch) piece of clear, rigid air line
tubing. The tube is cut at an angle on the end that sticks into the bottle
so that condensed moisture will drip off the end of the tubing instead of
getting forced up the tubing.

Drill or melt a clean hole just smaller than the tubing through the thick
plastic just below the top of the bottle, then roughen the plastic around
the hole and the outside of the tubing with a piece of sand paper. Force
the tubing through the hole (angled end first, with the point of the
angle-cut downward) with about 1/3 of the tubing in the bottle and the
rest out of the bottle.  Seal the joint with epoxy putty, feathering the
putty out on both the bottle and the tubing for maximum contact.  Don't
skimp on the putty.
In my first few attempts at this I used epoxy putty made for sealing
plumbing leaks.  The connections lasted a few months then loosened up, but
resealed well with 5-minute epoxy glue.  Since then I've been using a
higher quality, thick epoxy glue and the seals have been perfect for a
couple years.

If you have a leak you can usually tell by sealing the lid, covering the
outlet with your finger and squeezing the bottle.  You shouldn't hear
anything and there should be no loss of air from the bottle.  To be really
sure, do this test with the bottle under water so you can see any leaks.

> Is it better to make a sugar/water/baking soda mix, then, when 
> the co2 stops, dump out a little (1/2?) of the mixture in the bottle and fill 
> it up with the sugar/water mix?

There are a lot of things you can do to a mix; they're in the archives.  
I keep things as simple as possible because frankly maintaining yeast CO2
is drudgery and the less I mess with it the better. I like the way Dave
Gomberg describes it on his web site.  If you like washing dishes you'll
love yeast CO2.

Roger Miller