Potassium Sorbate
 

I just bought some cider from the store with which to make cider. I got back home and discovered that potassium sorbate inhibits the yeast, and is also added to the cider I just bought. Not having anything else to do with the cider (I've nowhere else to put it) I went ahead with the cider anyway.
But I'm wondering how long I should wait to see if the yeast is actually working, and how likely it is that it won't (the jug said 1/10 of 1% potassium sorbate). And would it help at all if I added more yeast?

I've never sucessfully started a fermentation with any juice that had sorbate in it, but I have heard it can be done. I guess you could pitch some yeast into some unpreserved juice and get it going well, and then gradually add your sorbated juice into it and see what happens. My gut feeling is that it won't ferment.

I made that same mistake on my first batch of cider, I gave it some time, tried repitching, making a starter from apple juice, the whole works and I was unsuccessful.

That doesnt mean you should give up on it right away, but if you try and get it going dont be dissapointed if it doesnt start fermenting.

On the Brewing Network, they said its possible, but you just need to pitch much more yeast to basically overpower the sorbate.

Any idea how much?

I think they made a yeast starter like I said in my post above. Get it really going well with apple juice, and gradually add your sorbated cider. If you really have a nice big fermentation going, you MIGHT be able to keep it going when you add your cider. Odds are against it, but maybe it's worth a try.

I had a couple of thoughts on this:

Potassium Sorbate is effective up to a pH of 6.5. Would it make sense to increase the pH of my mixture to, say, 7 using a a base, and adjust the pH to taste after fermentation? How would this affect the yeast?

Edit:
A starter with just sugar and water seems to ferment, so the yeast will probably be okay. It might make the mixture more prone to infection, though. If the fermentation gets going well enough the yeast might take care of that.

Edit #2:
Well, it's a better idea than just tossing the whole thing. I'll look into it sometime today.

I added some baking soda, used some pH strips to make sure it was at 7. Pitched some more yeast, and surprisingly, it seems to be working. Bubbling away at a fairly steady pace.

I made the same mistake with some store bought lemonade (1 gal) for making some hard lemonade. The first yeast did nothing, then I found out about the sorbate and ended up using strong starter from a whole packet of yeast (for 5 gal). Was a long slow ferment but it got there and actually tasted ok too.