I have a single Apple Tree “James Grieve” which I planted 3 years ago. This year there is a fair number of large fruit- We have had 2 or 3 windfalls in the past week (1st week Sept). The fruit is very firm to hard and lacks any sense of ‘sweetness’- There would appear to be no blemishes on any of the fruit and only small streaks of red.How much longer should we leave the remaining fruit on the tree before harvesting-or if picked does the ripening/sweetening continue or cease ?