Top Quality Appearance: Look for berries that are firm, dry, plump and smooth-skinned, with a silvery surface “bloom” and no leaves or stems.
Size: Ripe blueberries can be any size.
Color: Ripe blueberries are deep purple-blue to blue-black. Reddish or greenish blueberries aren’t ripe and won’t ripen once they are picked but you can use them in cooking. Or eat them if you prefer a tart berry.
Avoid: Soft or shriveled or moldy berries, which are signs that the blueberries are past their prime. Juice stains probably mean the berries have been crushed.