Low ABV Concord grape

[PossumPie]

I've been making wine off and on for 10+ years. My parents have a large grape arbor, but they are all Concord. We gather the grapes, wash them, smash them in 5-gallon buckets, and then run them through a homemade press. My parents don't drink, so they only want the grapes for jelly/juice, therefore I leave there with 5-6 gallons of juice. B/C the juice doesn't ferment "on the skins" it is always a blush wine.
I only made 1 gallon this year, Used a campden tab. the day before, added pectin the next day, and used champagne yeast (it was all I had) and I added sugar to bring it to 22 Brix. pH was 3.7 after adding raisins and lemon peel. Racked several times, it is clear and I bottled today. Tasted good (for unaged wine) but not completely dry, An alcohol value test showed ABV of only 4.7%. Usually I can get closer to 7-8% so I don't know why it stalled this year. Yeast stored in fridge, fermented at 72F. Definitely not dry-tasting, but no fermentation so I'm not worried about bottling. Any ideas?

 

[Ohio Bob]

22 Brix should give an ABV well over 10%. Are you using a hydrometer to measure the SG? Or a refractometer, which will yield erroneous results as alcohol in the wine will distort the refraction of light.

 

[PossumPie]

I use a glass hydrometer. I ended up with a half bottle left after bottling this afternoon, so I'm drinking it (hate to waste!) Even unaged it is pleasant, and more dry than I originally believed with a very small trace of carbonation and a distinct bite. I don't think there was a stall, I don't taste leftover sugar. I use a budget three-tube alcohol meter but it is very accurate, I've tested it against Everclear, wines with known ABVs, and vodka, and adjusted for temp it is spot on. The average alcohol by volume (ABV) of Guinness Extra Stout is 5.6% and I drink that, so I'm doing a highly scientific test where I'm drinking 12oz of this wine and see if I get a comparable buzz...!
One thing I left out that MAY be a clue, I had no wine to "top off" my gallon jug after first rack, so I used pure grape juice. The airlock was still slightly bubbling so I thought that would be fine, but maybe it didn't convert all the sugars from that added juice. It wasn't much, maybe 1/2 cup of juice...