If I add fresh yeast to something that had potassium sorbate added, will the new yeast restart fermentation? Or will the PS affect the newly added yeast too? Thanks.
I'm no scientist, but I do know that the PS keeps existing yeast from reproducing, thus it essentially stops fermentation after time. So it would seem that adding new yeast in enough quantity that does not need to reproduce to finish off the fermentation would seem to work for you up to a point. Hopefully someone with more knowledge on this topic will chime in.
Yeast really does not like sorbate very much. They can live with it, but are unable to reproduce in its presence. If you use a huge pitch of yeast, they can ferment past it. I believe the sorbate is permanent. Once you've added it, it stays in there. So your sorbated juice will affect your new yeast. Like I say, they'll live in there and do their thing, but once they become tired and settle out, that's all you get. They will not produce more yeast, so a huge pitch is needed.
You: “yeast, ferment!” Yeast: “yes sir!” You: “yeast, STOP fermenting!” Yeast: “really? um, ok.” You: “yeast, ferment again!” Yeast: “forget this. We quit.” You have lowered the morale of your yeast to the point where fermentation is pretty much done. Perhaps you should take some sensitivity training...
It is possible, but as others noted, not ideal. You gotta way over-pitch. Going by your other recent posts, I'm guessing you're trying to make a cider with sorbated juice. Either use something like 3-4 packs of dry yeast, or brew something low gravity that doesn't contain sorbate and pitch onto the cake. Pitching onto the cake would be more desirable than making a giant starter, due to the fact that if you're going to make as big of a starter as needed, it would be of a volume where you might as well get something to drink out of it. I once made a cider that contained 20% sorbated pear juice. I made it work by starting fermentation with 4gal unpasteurized, non-sorbated apple cider and once fermentation was going, adding the gallon of pear juice. Came out well. Going by your other recent posts,I gotta say, it's cool that you're trying to make something gluten-free for (I'm presuming) a loved one, but it takes a lot of preparation (mainly sourcing). If you don't have a source for non-sorbated juice, a cider will be hard to pull off. Maybe try a mead? Most LHBS also tend to carry a variety of wine kits, and Briess makes a sorghum extract if you'd like to try your hand at gluten-free beer.
