Years ago at the AGA Convention in Dallas, Tarah Nyberg presented a talk about how to generate CO2 with optimized conditions. She was a graduate student at UT Southwestern Medical School in Dallas getting her PhD in yeast genetics, so I figured she knew what she was talking about. Anyway, here are some of the points that she emphasized in her talk and that were put into practice in my tanks.
1) Yeast do not tolerate ethanol and sugar above 10% total volume. So, if you use 2 cups of sugar (500ml) per 2 liters of water, your sugar concentration is 25%. That's 15% of the sugar wasted, since yeast quit fermenting after the ethanol reaches 10%. So, I used to use 1 cup of sugar/2 liters of water which will be below the ethanol tolerance of the yeast.
2) Yeast need additional nutrients to stay healthy. When the yeast is rehydrated, they have a store of proteins that is used in fermentation of sugar to CO2. Over time, that store is used up and the yeast will need nutrients to supplement their "diet" in order to synthesize the proteins needed to continue fermentation. Tarah recommended adding 1-2 teaspoon of a protein mix (just make sure it has proteins and vitamins and minerals), or if you can find some yeast extract, that's even better.
3) (Optional) Yeast also like ammonia, so add some ammonium sulfate (1 teaspoon) or 1 tablespoon molasses as an ammonium source. I skipped this step and my fermentation was fine.
4) Buffer the yeast with a bit of baking soda. The pH of the solution will drop during fermentation, so adding a buffer will keep the pH in the healthy range for the yeast. I used to buffer between 7-8.
5) Use champagne or wine yeast, both of which are more tolerant of higher ethanol concentrations. I had great luck with a strain that was not only more ethanol tolerant, but also temperature tolerant. Yeast like to be warm, but the champagne yeast I used even worked well at low temps (especially important in the winter).
6) Finally, decant to liquid part and retain the yeast sludge at the bottom of the bottle. The healthy, growing, fermenting yeast are in that layer. The stuff that's floating (flocculant yeast) is dead and should be poured out when you make a new mix.
I used a 3 liter wine bottle for my container and make 2.5 liters of the mix each time. I was able to generate a slow steady release of CO2 for 3-5 weeks depending on how long I had the yeast. I reused the same yeast for over 2 years before I finally converted full time to a Co2 system. Hope that helps some.
Forgot to add, I only used 1/8 a teaspoon to start up the yeast. It might take a bit of time to get going, but the density of the yeast will increase gradually and utilize the sugar in a more controlled fashion. If you use too much yeast, it starts up too fast and you end up getting a CO2 spike followed by a fairly rapid decrease in CO2 generation. By using less yeast, the yeast will multiply to equilibrium where the yeast multiplying equals the yeast dying. If you use too much, the yeast will burn through the sugar to the ethanol limit and then they will start dying off until levels can be maintained in equilibrium. Hope that made sense....
Last edited by Darkblade48; 11-22-2013 at 03:12 AM.
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