I'm new to this form, but another reason you saw no bubbles might be that yeast don't eat certain sugars. I read that they don't eat steevia (not a sugar) and they don't eat the sucralose. I'm not sure why but I heard it is because they can't digest it.

So I'd like to add that because they can't digest it, if you are on a strict diet eliminating all sugars, etc..then as a result the yeast starve and are killed, but you get the benefit of having a sweet flavor....yet, I'm always not very trusting of denatured sugars though...if it hurts one lifeform and they won't eat it, what does it do inside of us? I always will remember that even mold won't eat Mickey D's...is that due to the perservatives or do they know something we don't about it?...(Supersize Me) I don't know enough about Sucrolose.......

Are bubbles really evidence that the yeast are alive? or evidence that they are digesting and releasing toxic gases after digestion into the water? That might be interesting to find out....?