Tips for eating Japan grapes

It may require a bit of experience but stronger the colour is, the sweeter the 
grape is. Also, the gloss decreases as the grape ages.

It is like a human! The aroma gets stronger as it ripes but there is no clear cut border line between a well ripen and too ripen. It is very subjective for a certain degree like Sushi or prestige wine. The individual piece becomes very soft when it goes out of date. This is the easiest way to judge.