Starch-Sugar Conversion
Starch-Sugar Conversion is when fruits break down stored starch into sweet sugars as they ripen.
Think of it this way
A bag of sugar in a pantry holds energy ready to use right away. A bag of flour holds that same energy, but locked inside long chains that take time to break apart. A ripening banana works the same way — its starch chains slowly split into small sugar pieces. That is why a green banana tastes bland, but a spotted one tastes sweet.
Explaining starch-sugar conversion by grade level
A green apple tastes sour because it has starch in it. Starch is not sweet at all. As the apple gets ripe, it turns starch into sugar. That is why ripe apples taste so much sweeter.