To me, once a jabo is beginning to get soft, it is over ripe. My way of knowing when ripeness is perfect is by size and more importantly, the way the fruit is held by the tree. When ripe, the fruits sort of hang slightly and are no longer held out at 90 degrees from the trunk. But, this can be a bit deceiving when there is very thick fruit production. The fruits cluster so tightly that even the most mature, ripe and full fruits are held in place by th other closely held fruits. That's when size of the fruits is my guide. My preference is for the fruit to be very firm with no give. I pop the whole fruit in my mouth, pop it open, enjoy the white flesh and spit the seeds and skin. I never have any issue with the skin either in tartness nor tanin. And I am very sensitive and do not care for tanins. So, I am not sure how anyone is enncountering any problem with this process.
Harry