This post is actually something that I just sent out to a mailing list (more on that later) that I thought I should probably put here for future reference. If anyone does have solid numbers to share as far as alcohol content in soda, I would love to see them!

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While I don’t have any hard numbers to share for an answer, I’ve
always been told that the actual alcohol content from naturally
carbonated sodas is very, very small. A fairly simple way to look at
it is that when you brew beer, you let the fermentation run for weeks.
With soda you let the fermentation run for days and then slow or stop
the fermentation to keep your bottles from exploding.

I usually let me batches of soda run for about 3 days (60 hours
actually) at between 65F and 70F to get the carbonation level that I
like. After refrigeration (I have a separate bar fridge that I use
that is set to 45F) fermentation does continue, but at only a small
fraction of the pace.

Fairly normal beer brewing instructions say to run your first
fermentation cycle for 3 to 7 days and then to do secondary
fermentation (for carbonation) for 2-4 weeks, all at 65F to 75F. Even
if fermentation is a fairly constant process (which it isn’t quite)
the comparison between 3 days to 28 days of fermentation should tell
you a LOT about the comparative alcohol content of your soda.

A quick google search turned up a really good article on how to
calculate the alcohol content yourself:
http://science.howstuffworks.com/question532.htm

The article in particular is talking about beer but the actual
measurements are certainly valid for soda. You do have to take some
measurements at the beginning of a batch in order to make the
calculations work, but that’s just a good excuse to get another one
going isn’t it?

Maybe I’ll get around to doing a real test with various sugars to get
some real numbers for the next time somebody asks.