DIY Yeast CO2 Short-Lived

[tackful]

My initial attempt at diy CO2 seems to be quite successful. After a day or two I noticed bubbles rising up from my larger plants. In particular, the Wysteria in the corner are growing quite well. The advice from AC has been paying off!
The next step in my co2 setup involves finding a mixture that will last for more than six days. That bottle, my first, contained 2 cups sugar, 3/4 teaspoon baker's yeast, and water up to the round shoulder of the 2 liter bottle. I've just started a new batch, this time using only 1&1/2 cups sugar. I'm simply experimenting to see if I can get more than one week out of a bottle. Is this the right way to proceed? Any suggestions?
One more question: why don't bubbles stream from my diffuser shortly after appearing in the bubble counter bottle? There seems to be a delay of several hours.
Once again, thanks for the help. This sure is an interesting hobby. Tackful

[TropicalNorth]

I've found the ratio of 1/4 teaspoon of yeast to 2 cups of sugar in a 2 litre bottle can last up to 14 days (starts to slow down at 10 days though). Basically you want a smaller amount of yeast to a larger amount of sugar, this way it will take longer for the yeast to 'eat' the sugar and therefore will produce CO2 for longer. If you use too much yeast it will consume all the sugar in the beginning, produce a lot of CO2 to begin with and burn out quickly.

Your doing the right thing, just keep playing around with ratios of yeast/sugar until you get what you want. In my 20g I found 2 2 litre bottles with the above yeast/sugar ratio worked best for my tank.

[Rex Grigg]

There is a very basic misunderstanding of how yeast works. Yeast is a plant. It reproduces quite quickly. So it really doesn't matter if you start with X, 4X or ¼X yeast. You are only delaying the time line by the amount of time it takes the yeast to reproduce that many generations. The amount of yeast is NOT static.

Say the yeast reproduce every 2 hours. You start with X. In 48 hours (24 generations) you will have X to the 24th power.

If you start with ¼X after 48 hours you will have X to the 20th power.

Bread yeast doesn't run out of sugar. It dies from alcohol poisoning. You are best off using a good wine yeast that is more alcohol tolerant. In fact if you use the right yeast you actually run out of sugar before the yeast dies and can re-use the yeast time and time again.

[Squawkbert]

Rex - you're right, but it does matter at least a little - especially in the beginning.

I have not tested it yet, but I suspect that controlling the surface area of your yeast vessel will have a lot to do with the "burn rate" of the sugar, at least w/ the top fermenters, like bread yeast, that most DIYers use.

In theory, having a large surface area would allow for a larger population of yeast - leading to a higher CO2 production rate (and shorter bottle life). For people using Champaign or other bottom fermenting yeasts, it's all about how much yeast they start with (assuming they've got the right sugar/water ratio) - unless they want to start controlling temperatures.

[wesknox]

Squawkbert:

You hit on the thing I was thinking about...temp control. If your reactors produce CO2 more rapidly than you need to inject it, you are just creating pressure/production more rapidly than you need. If you could create a feedback mechanism that adjusts brew temperature as a function of bubble rate, you might extend the process yet further...although you'd spend more money on a chiller than you would to buy bottled CO2.

[tackful]

Thanks for the help; I understand the alcohol effect and will try wine yeast. One more problem: my new batch has been producing a bubble every 3 seconds in the counting bottle, but after 8 hours still nothing comes out of the glass diffuser (a $15 ADA copy). I thought the check valve inside was stuck, so I got that loose, but it's still not working (it seemed alright before I changed bottles.). I checked for leaks, found none. Where's the CO2 going?
Until I figure this out it's back to the airstone. Thanks again. Tackful

[easystreet]

i have noticed it takes quite a bit off pressure to get through the glass diffuser on my unit.. i would say wait it out..

[mellowvision]

I have one of those ADA copy's I got on ebay. it worked great for 2 days, and then I left it in the tank but disconnected for 3 days while on vacation, and now it's clogged solid. I can't even blow air through it with my mouth. something tells me they are a lousy product.