It is very possible that the wine has undergone spontaneous malo-
lactic fermentation. A good bacteria converts the malic acid into
lactic acid, which has a slightly higher pH and lower acidity than the
malic acid. This serendipitous occurance should soften the acidity of
the wine, increase the mouthfeel and make it effervescent as it ages.
Keep the bottles cool in the summer or you may begin to lose some
corks prematurely. Enjoy it.