Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
As long as you keep adding more sugar, and diluting the alcohol with more water, it will work.
But there is one important difference between DIY and "friendship cake". Fruit has all the nutrients yeast need to multiply. Refined sugar has barely any nutritional value at all, and so many of the nutrients are limited, present mainly in only the yeast itself. That's what keeps yeast from multiplying endlessly and allows us to select a production rate by adding a certain amount of yeast.
So if water is ever replaced, you cannot remove any of the yeast, or the new solution will have a lower max population and production rate. You can add other nutritious ingredients, but then might end up with higher population and production rate. Neither is desirable in DIY CO2.
Folks who use expensive champagne yeasts for DIY wait for it to go dormant, at which point it sinks to the bottom, and the water can be carefully decanted off without losing much yeast. This works well enough to restart the DIY several times before production gets too far off the desired rate.