Red and black cherry varieties must show what characteristic when picking for optimal maturity?

The characteristic that red and black cherry varieties should exhibit for optimal maturity is that the entire surface has attained a light red color. This indicates that the cherries are mature and have developed their full flavor profile, which is essential for quality and taste.

Cherries need to reach a certain color to signal that they have ripened properly. For most cherry varieties, including red and black types, a light red hue across the entire surface is a good visual cue that the fruit has reached its peak maturity. This is important because picking them before they've fully colored can result in a sour or unpalatable taste, while allowing them to over-ripen may lead to overripeness that affects texture and sweetness.

In contrast, other characteristics like a uniformly green color or starting to shrivel indicate immaturity or overripeness respectively, both of which would negatively impact the quality of the cherries if harvested at those stages. A dark maroon color suggests overripeness in many cases, leading again to less desirable fruit. Thus, the optimal characteristic to look for when determining the right time to pick red and black cherries is the attainment of that light red color across the entire surface.