Particularly efficient spontaneous fermentation

2 weeks ago I started a spontaneous fermentation project using 2 and a half quarts of cheap, from concentrate apple juice(112g sugar per ounce), 8 ounces of black cherry concentrate(28g sugar per ounce), and about 16 ounces of juice from 3 lbs of ground up granny smith apples. I'm estimating the fresh juice contributed 50g of sugar, based on the sugar content of a cider like Musselman's.

So I had approximately 610g of fermentable sugars in approximately 3.07 liters of must. I had yet to buy a hydrometer at the time I started this one, so I can only estimate the original gravity, but those numbers should put this one at 1.0766.

For the first 7 days nothing happened, but by the end of the 8th I had quite visible signs of fermentation. By the end of the 9th, it was so vigorous and foamy that I had to replace the airlock with a blowoff tube. Today, 15 days in, the bubbling at the airlock had slowed to once every few minutes, so I transferred to secondary and strained the slurry into a half liter soda bottle to save for future experimentation.

The current gravity reading is 1.002, which fits with the extremely dry taste of the sample. That should put me at ~9.6% abv, far higher than what I was expecting from spontaneous fermentation.

How does this compare to results you guys have had?

there is no reason that your fermentation should/will stop before all the sugar is eaten, if your estimate of OG is anywhere in the ballpark. it is likely to finish around ~0.994 give or take a few points

All my wild fermentations have gone totally dry.