Wine juice conundrum

I am holding three Paul's of juice for a friend until Sunday. I received wed night, and 50 ppm to all three last night. Tonight I noticed one of the three, the cab sav, started fermenting. I didn't run into any issues with the other pails, a Chardonnay and a Pinot Grigio. What gives? For what it's worth I had three pails of Chardonnay and three pails of Pinot noir that didn't have an issue either and I very lightly sulfited those as I am putting them through mlf.

Are the Paul's refrigerated or at room temperature? If they aren't cold maybe putting them in a container and surrounding with ice will slow down the wild fermentation? If not call him and ask him what yeast he wants to use and pitch it, quickly. If you add too much Kmeta and he wants to MLF it might be hard to overcome the Kmeta.

Pails are room temp. What boggles my mind is I added the same sulfite level to all three containers. Only one started. I have added ec1118 to the Pinot noir but am still trying to understand the wild ferment. My calculations have the ppm over 50. In the past this has always worked for me to stop wild fermentation

I don't know where you are located and what brand of juice you are using but I have used Mosto Bello Italian juice, Regina California juice and L'uva Bella California juice. All are inoculated with yeast when purchased. Having wine start fermenting in the pails is not uncommon. Do your pails have a pressure relief valve on top? All of mine do and I have had them actively fermenting even coming out of the refrigerator at the supplier.

In any case, the one that is more active, the Cabernet Sauvignon, needs to get into a fermenter soon.

I was told there was no yeast added by supplier, just 15 ppm sulfite. It will be put into a carbon tomorrow so I am not overly concerned, just confused as I figured the sulfite levels would keep wild yeast from fermenting. None of the other pails received, 8 others, had an issue of starting fermenting on wild yeast

Adding sulphites wont keep the yeast from working, it just slows down wild yeast until your chosen yeast takes over. I'd pitch very soon!