Maybe this is a really dumb idea. But the other day I got to thinking. Here I am buying 2 liters of pop and drinking them so that I'll have a bottle I can put yeast into to make co2. But what about just hooking up the pop bottle itself full of pop?? That's full of co2 already with no mess! The obvious problem firstly would be that all the co2 would leave really rapidly so in two or three days you would have none. But you could put a check valve on it the same as a cylinder would have to regulate how much is allowed out at once, to make it last longer. The other issue would be cost, but when you figure out how much it costs to buy 2 cups of sugar to put into your yeast plus all the hassle, mess, and inconsistent results, maybe it would be worth it. How long do you think this would last?? I might just try this for fun.

Hm. Sounds like I need to experiment with this!

If you assume that there is a solid method for extracting the co2 from the bottle and was able to control the flow rate into some tank here are some numbers to look at as far as how long it would last:

The average 2 liter bottle of soda has like 12 grams of Co2 inside.

454 grams is = 1 pound.

So you would need like 35 x (2 Liter bottles) of soda to = 1 pound of Co2.

In the States a bottle of cheap soda is like $.75.

For 1 Pound of Co2 using Soda you'll spend $26.25

I get my 15 pound bottle filled for $9.00 which would be equal to some 525 bottles of Soda.

How long does your 15 lb bottle last?

I wonder how it compares to using yeast. That doesn't take into account the initial outlay of money for using pressurized co2. But obviously in the long run if someone has large tanks in particular, using pressurized is cheaper. What I was thinking was that if one bottle works for a month or even two weeks, I don't mind paying $2/month as opposed to messing around with yeast. I don't have the funds right now to invest in pressurized co2.

I set it up tonight but found what I think will be the problem that will make using it impractical. The issue is that since you are not producing any co2, as co2 is released from the bottle you eventually get to a point where there is not enough pressure in the bottle to put out any more bubbles into the tank. Right now I have the valve 100% open and I'm not really sure if it is still releasing bubbles or how much it will continue to release or if it will stop releasing it.

You might try putting the bottle in a warm water bath. Warm water holds less CO2 in solution than cool water. The flaw I see in your idea is that you have to open the bottle to install your CO2 outlet on it, and that lets a lot of the CO2 escape. You could possibly minimize that by almost freezing the bottle first.

That's a good idea. In fact I have a heater I can use to heat the bottle...great idea! I'll try that.

The thing too about starting off is that initially there is a lot more pressure, then as the excess co2 comes out into the tank the amount of pressure inside the bottle drops very quickly. So to allow it to escape at a slow rate, you have to readjust your valve every 5 minutes. But the freezing/heating idea might work! As of this morning I don't think anything was coming out of the bottle, unless I would shake it up. Then a whole bunch would come out of course, then nothing again. I'll try the heater thing and see what happens!

Well, it proved to be impractical since once enough co2 would leave the bottle to equalize pressure, it would stop putting out bubbles. The only way I could think that this would work practically would be if you had an air pump on the hose sucking out co2 at a regular rate.