Jim Lewis wrote:

You aren't peeling enough off. Go deeper than the reddish pink layer,
down to the bare yellow(ish) WOOD. That reddish pink stuff is the
"live" part (cambium) of the tree. It dries to an ugly brown after
exposure.

Hi Jim
but how can sap flow into such dry bark , I expected to
find something more soft & juicy 2-3 mm thick

The wood itself should be immediately under that very thin
layer.
when Iu cut in with a knife it looks like to cut into
wood not bark .. after that live"veins* are formed how long
will it takes before they thickens, any idea ?

Thanks
Tiziano