I made 5 gals of cider with fresh pasteurized cider from a local farm last September. Put it in a carboy with 2lbs sugar dissolved, and topped it with a packet of cote du blancs yeast. It fermented out, aged it for a year in the carboy. Then 2 weeks ago i bottle it and it carbed up, some carbed quite a bit. Champagne like carbonation. Could it be it didnt ferment fully, that the russleing of bottling stirred it up and it continued to ferment, after 1 year? I can think of no other explanation. It hasnt been long enough for infection.