I'm wondering if there's any way to kill the preservatives in store bought juice. I was thinking about boiling it at high temperature for like 5 minutes, but not sure if it'll work. If anybody has a solution, I'd sure love to hear it ! A friend of mine makes mash out of store bought juice, but won't tell me how he does it to kill off the preservatives. "TRADE SECRET", he says.......
Some pasteurised juices don't contain preservatives. In Europe for example the budget supermarkets ALDI and LIDL stock pasteurised apple and grape juice that is not from concentrate and contains no preservatives. They ferment very well.
Sulphites, sorbates and benzoates and similar preservatives generally interfere with yeast growth. So fruit juices that contain these preservatives can be fermented by the addition of fully active and concentrated yeast cultures. The yeast does not need to "grow" just ferment - so introducing all the live yeast needed in one go will usually work. Its not ideal but it does work.
To get rid of the Potassium Sorbate (which is common as a juice presevative), it must complete its purpose, which is to prevent yeast to multiply (and mold to grow).
So it can prevent fermentation from starting, but it cannot really stop an active fermentation. Which means you need to use an active yeast starter.
Then, if fermentation slows down before its time, racking and adding more active yeast one more time should work. The more Sorbate there is, the more yeast it can control. To illustratrate this, lets say that Sorbate will "attack" the yeast and be "consumed" afterwards.
About the same thing goes for Campden (Metabisulfite), it protects the wine from oxygen, but once it is combined to oxygen molecules, the Sulfite is consumed and one would need to add more to continue the protection. So to remove Sulfites in a wine, you need to expose the wine to oxygen for a certain amount of time (vigorous mixing would do!).