I recently fermented Kedem brand grape juice (which contains potassium metabisulfite) by only adding rouge red star yeast (and slapping on airlock and leaving it on my kitchen counter). I recently got into a discussion if there is any way to ferment it without adding any ingredients at all - stirring, refrigerating, leaving it outdoors, adding an airlock etc. would be allowed (this may have some applications to an esoteric aspect of Jewish law). Does anyone know if its possible or will the wine spoil first?
The chances of this working are about zero. It will eventually ferment, but the results will probably be bad. If you want to get yeast into the grape juice in a natural way, you can put a piece of fruit or berry into the grape juice. The best thing is to find some Organic grapes at your local grocery. I say Organic because there will be a better chance they have more robust yeast colonies on the skins than non organic. The "bloom" on the skins of the grapes is made up of many different yeasts and bacteria, but usually the best for making wine will survive.
I would put the grapes, minus the stems, in a blender for a little bit and then dump the whole mess into your grape juice. You should see fermentation within 24 hours. When the fermentation is done, you'll need to drink it quickly unless you put more sulfites in the "wine".
If you won't/can't put some fruit or grapes in there. Put it all in a big clean bucket outside on a nice sunny day with little or no wind. Preferably near some flowers or trees (you want the pollen to fall in there). Pollen contains a lot of yeast. You only need it outside for an hour or so. Then put it in a carboy or just cover and let it try and ferment. It might or might not work but this is how they make spontaneously fermented beer.
BTW, all the Metabisulfite in the juice will be blown off in the fermentation process so you will need more to keep it preserved afterwards.
It is possible it could work, but you have to be pretty lucky. The chance of getting some local acetobacter or wild yeast that could survive and spoil the wine would be high.
If you have a bunch of grapes and used them to prime your grape juice, that could be a better way than just stirring outside, as the yeasts on the grape skins are what was the fermentor historically.