The message
from "kc" contains these words:

I have an old oak tree (probably as old as my house--81 years old)...I'm
trying to treat it well so that it will last even longer...today I was
pulling ivy off the trunk and I noticed that there was a distinct smell of
vinegar coming from the tree bark. When I leaned closer, I confirmed it
was definitely coming from the tree--kind of a clean smell, like apple
cider
vinegar but I find it strange!

You're probably smelling tannin, a natural preservative in oak bark.
It used to be harvested for the natural preservation of animal hide, to
make it into leather.

Janet.