>I use 2 cups of sugar (.5 liters), with 1 tsp of yeast (2 ml?) and 1 tsp of 
>baking soda in my yeast generators.  The bottle is a 2-liter soft drink bottle 
>with a fitting in the cap for the air line.  I fill the bottle to within 3" (8 
>cm) of the top with lukewarm tap water.  After hooking it up, I start getting 
>bubbles within 20 minutes, and I get full strength in about 1 day.  It 
>continues to bubble for about 3 weeks

David, sounds like what I tried but I only get about 3 days of production. 
What temperature would you guess your bottles are at?    

Dave Gomberg, Experimenta      San Francisco CA USA   gomberg at wcf_com