I tried making another bottle of vanilla cream soda, but not the single-bottle method. Instead of putting the sugar and yeast in that bottle, I put them in another bottle (along with orange flavor) and connected the bottles with tubing glued into the caps. The idea was that the bottle of orange soda would use the sugar and yeast to produce carbon dioxide and pressurize both bottles. It didn't work. The air in the bottles and tubing was compressible enough that pressure never really built. I even put some Silly Putty around the tube-cap seal to see if the seals were bad - they weren't.
I gave up and removed the tubing arrangement and put normal caps on both bottles. The orange soda is coming up to pressure. As it sat out quite a while, it might well have a noticeable amount alcohol.
I chilled the vanilla cream bottle overnight and used the tubing setup again. This time with a baking soda and vinegar setup as a carbon dioxide generator. The whole works is in the fridge so that the seal won't be broken until the gas has hopefully dissolved.
Over a month ago I got adventurous and set up an arrangement inspired by this article. I stuck with the 2 L bottles and tubing I had, and use substitutes for almost everything. The fermenting bottles and such all got cleaned with bleach, to be sure of things.
I didn't have any beer or ale yeast. I didn't have any malted barley. I didn't have any hops. So instead of beer or ale yeast I used the champagne yeast. Instead of the malted barley I used sorghum. Instead of the hops I used ginger. Instead of the water... okkay, that would have been a real trick. I used ordinary water. This stuff would never meet the old German beer purity law, but it works (after a fashion) just the same.
I let the setup go for about a month and then filtered the ginger out, added a bit of sugar (I might not have had to - I think that's done to feed the yeast for the final carbonation), and poured the brew into some 8 oz. plastic bottles and let then sit for about a week. The little bottles firmed up nicely as the pressure built. I put one of the bottles in the fridge late last night.
We had that bottle at the start of supper tonight. For a first try, it's not bad. It's not what it should be as there is an odd feel to it that indicates I used too much sorghum for the amount of everything else. But it did smell like a beer. It had a noticeable alcohol content. It bubbled. And even with the excess sorghum defect (made it sweet and a bit slick feeling) it had some character and wasn't a forgettable thing. It's not what it should be, but it's certainly not a "pour down the drain" failure.
So I think I'll do it again, but I'll get one of those big 3 L soda bottles to use as the fermenting vessel and scale up the water, ginger, and maybe yeast - but not the sorghum. I'll also do the final bottling with soda bottles that are made to take pressure. The 8 oz. bottles held plain water.
Meanwhile, I have a few of those 8 oz. bottles of this stuff left. I did partly unscrew them today to vent them. One was hissing due to excess pressure and/or an imperfect seal. Another week might do them some good, but I'll be monitoring the pressure.