Anyway, my hypothesis was that Coke Life would have the most growth, even though regular Coca-Cola had more sugar because, as I theorized, the yeast had evolved to eat sugar, not high-fructose corn syrup. I was wrong. Diet Coke seemed to produce the most gas before it stopped, but in the graphs, regular Coke was pretty much identical to Coke Life. And I had not expected Diet Coke, which contains no sugars at all, to have any growth. As it turns out, the balloon was being inflated by residual carbon dioxide from the soda and not from the fermentation. And about the extreme jumps in Regular Coca-Cola and Coke Life, it's because until 1 hour, I was recording the radius of the balloon, not the volume. OOPS! But the radius was correct.
To try to remove the external variables involved in doing Coke (like artificial colors, caffeine, and carbonation), I did a second experiment with just water and the same concentrations of sugars as the Coke. It worked much more as I had expected the Coke experiment to work. Here is my data from that experiment.
0 grams of sugar
7 grams of sugar
11 grams of sugar
Apparently it isn't more sugar that impacts the yeast growth. Apparently there's a "sweet spot" (pun intended) around 7 grams that seems to provide optimum yeast growth. Stay tuned for experiments including stuff like how yeast react to artificial sweeteners, brown sugar, and other sweeteners.