Look for: fresh blueberries that are firm, dry, plump, smooth-skinned and relatively free from leaves and stems.  Size is not an indicator of maturity, but color is—berries should be deep-purple blue to blue-black; reddish berries aren't ripe but may be used in cooking.

Stay away from: containers of berries with juice stains which may be a sign that the berries are crushed and possibly moldy; soft, watery fruit that means the berries are overripe; dehydrated, wrinkled fruit that means the berries have been stored too long.

Fresh berries should be stored covered in the refrigerator and washed just before using.  Use within 10 days of purchase.

Blueberries may change color when cooked.  Acids, such as lemon juice and vinegar, cause the blue pigment in the berries to turn reddish.

Blueberries also contain a yellow pigment which, in an alkaline environment, such as a batter with too much baking soda, may give a greenish-blue color.

To reduce the amount of color streaking, carefully fold blueberries (right from your freezer, if frozen) into your cake or muffin batter last.  For pancakes and waffles, add the blueberries as soon as the batter has been poured on the griddle or waffle iron.  This will make the pancakes prettier and they'll be easier to flip.  If frozen blueberries are used, cooking time may have to be increased to be sure the berries are heated through.