The surface of fresh grapes is often covered with a thin white film, which many people mistakenly believe is pesticide residue. In fact, this film is a good thing.
Generally, any white film that is evenly distributed and does not cover the grape's natural skin color can be considered a natural substance secreted by the grape itself, known as bloom or pruina. It is completely harmless to the human body and serves as the grape's "protector." Since these sugar alcohols are not water-soluble, they prevent the grape's surface from absorbing moisture, which would otherwise create a damp environment conducive to the growth and infection of pathogens. They also stop the grapes from shriveling by losing water too quickly after being harvested. Furthermore, the wine yeast rich in this bloom can prevent microbial contamination during the winemaking process. Therefore, when selecting grapes, do not intentionally avoid those with this film. In some cases, the amount of bloom can be an important indicator of grape quality.