I hope someone can help me with a tricky decision about what to do with a batch of cider that I accidentally double dosed with metabisulphite. I intended to kill the wild yeast prior to pitching yeast into the 30 litre (8 gallon) bucket full of apple juice I juiced myself. After two apparently failed yeast pitchings, I retraced my steps and realised I had double dosed. To get the metabisulphite concentration down to normal again, I decided to split the juice into two buckets and top up with more juice. I also decided to use a starter bottle to get the yeast going prior to pitching this time, as I read that this can help with troublesome juices.
So when I cracked open the bucket to do this, 7 days after the previous supposedly failed pitch, it was clearly very fizzy, even though the airlock had not been bubbling. I am certain I have no leaks. I think a fermentation must have started very recently, which had not yet created enough outgassing for bubbling. I measured SG and didn't register any change, but I have a margin of error with that on account of all the scum and detritus on the top (kitchen juicers produce this). Now that I have split it between two buckets and added more juice, diluting the metabisulphite, I have crazy bubbling going on, three or four bubbles a second in both buckets.
My interpretation is that some yeast survived the double dose, was just about to get going properly after a week, and is now going crazy without the extra metabisulphite. But what I worry about is this. I know that yeast which has been stressed can become worse. Presumably what survived are the few yeasties with high metabisulphite tolerance. These might not be the best ones for finishing the fermentation. I did get a starter going on sugar water at the same time. These yeasties have not been stressed. Should I add this starter in to try and get some non-stressed yeast in there, or should I just leave well alone?