Mold growing on must

Hello all. I'm a long-time brewer and am now advising my father-in-law on making Perry, since he grows oodles of astringent, old-english pears that are perfect for this brew. He decided to try fermenting wild, and has had the must in his carboy for about 3 weeks at rather cold temperatures (40-50's F) as suggested in the book he has been following. There is a nice line of mold growing along the top of the must, and has been no visible activity in the airlock, so we tried measuring some properties, and find the sugar content has dropped 1 Brix (16 to 15) in 3 weeks, at a surprisingly low pH of 3.3. Honestly I have no idea what things should look like when doing a wild fermentation but the presence of the mold at this low pH surprised me.

I suggested that maybe we pitch a little commercial starter like Montrachet yeast in, just to give the natural beasts a little help, and that maybe keeping the carboy at "outside temperatures" as recommended in his British manual could be too cold for this process.

I can provide photos of the pears or the crud in the carboy, if anyone needs. I figure this is less a Perry-only issue and more a wild-yeast question, which is why I posted here.

Happy thanksbrewing everyone!

-ben

I should add, the mold is light/pale green in color, and there is a decent bit of it, as a ring about 1/2-in wide going across about 40% of the edge of the carboy.

In thinking more about a mold infection, perhaps racking the liquid out into a clean carboy, nuking the stuff with Campden tabs and then pitching yeast is best?

-b

Have you done anything with this?

After a couple more days a lot more mold had grown so we racked it off, nuked with campden tabs and pitched champagne yeast. It's only been 2 days but the yeast made a great krausen and no signs of blue/green friends...