"LG1111" wrote:
That makes sense, but on a really simplistic basis, when you taste a fresh
grape, the juice tastes sweet and the skin tastes tart. That must mean
that
when the juice and skins are fully fermented, the resultant must is more
acidic
than the starting juice.

That also makes sense, but .... try the same test after 24 hours of
fermentation (or cold-soaking), and you will see that most (if not all) of
the tartness (but not tannin content) has been adsorbed by the liquid must.