Ripeness is often only referred to by sugar content of the berries, but as the previous comments state, especially phenolic ripeness, flavor compounds, berry skin texture and seed color and flavor, and even texture, do give good indications about ripeness and a balanced state of the berry. Living in a cool climate (Germany), I also do find specifically interesting that the amount of malate is significantly higher here than in hotter climates like California, and that that of course has an impact on flavor profile of the berry - and the resulting wine. This is something that cannot really be managed with longer hang time, as it is simply tied to the climate and temperatures in general. So, the important factor of acid content for ripeness is in my view equally important to sugar content, and above all an aroma profile that needs to be according to ripeness and desired wine style. Interesting side story: I had a pinot blanc from the Moselle yesterday, and it had an incredibly harsh taste of malic acid. The winemaker told me that he didnt really know how to handle pinot blanc as he was used to working with Riesling. So he harvested the pinot early and made a "less aromatic" wine from it, although letting it go through malo and aging it in a new oak barrel. I would want to say that it was unfortunate, as the wine itself was lacking aromas and had such high acid! So harvesting rather unripe grapes, will result in less aromas and in my view can produce a more stable (due to low pH) but also more uninteresting wine.