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I was talking with someone who works at Kedem grape juice. He told me that although they put Potassium Metabisulfite in their grape juice by the time the manufacturing process is done and you actually open your grape juice there are only 2-3 parts per million of "free SO2." That number seems incredibly low to me. Is it possible that he's correct or is he for sure wrong?

(Note it does say "contains sulfites" which is only necessary if there's at least 10 ppm, but it could be that they calculate this at an earlier stage or that they calculate total SO2, not free SO2.)

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    If the label says from concentrate, the so2 is probably added to the concentrate but then diluted out when they turn it back to juice.
    – Evil Zymurgist
    Apr 23, 2018 at 13:29
  • It's entirely possible. Is this juice fresh, frozen or pasteurized? I have a feeling it's pasteurized, which will screw up any winemaking attempt you make.
    – farmersteve
    Apr 23, 2018 at 16:32
  • I went back and looked at your previous question on Kedem juice. What's the purpose of fermenting this? Concord grapes make notoriously bad wine...
    – farmersteve
    Apr 23, 2018 at 17:07
  • @farmersteve Correct. I'm not interested in it for the flavor (although it was pretty good when I tried it in the middle of the fermentation- not so much at the end). The reason why I care so much about this is due to an esoteric aspect of Jewish law.
    – Eliyahu
    Apr 23, 2018 at 17:20

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It is possible he is correct. The reason they have the message required for 10ppm is that probably the mean is 2-3ppm, but if something happens in manufacture that requires a large dosing then the level detectable is higher than 10ppm, this may be a rare occurrence or due to natural fluctuations in raw materials that require differential treatments.

It is as you state possible that they monitor this at an earlier stage, or that free and total are differently measured.

I would suggest there is no reason not to trust their statement, but we must accept that there may be variability.

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