Bloom is a protective, natural wax coating on the berries.
When you’re picking in the blueberry fields this summer, take a closer look at the many shades of blue covering the bushes. Berries don’t all ripen at the same time and the developing fruit may be green, purple, or a deep blue. Many of the ripe ones even appear a dusky shade of light blue, caused by a thin white coating on the berry. That color is caused by bloom – a natural wax produced by the blueberries to help protect their skins from the elements.
Bloom is a naturally-occurring shield on other fruits – such as apples and pears too. If you have ever shined an apple on your shirt before taking the first bite, then you just wiped off the bloom!
As a natural product produced by the plant, bloom is safe to eat and helps preserve the fruit longer. But don’t worry if your fingers wipe off some of the waxy coating as you pick! Blueberries will keep for up to two weeks if kept dry and stored in the refrigerator.
Jones' Farmer Blog 