Washing grapes before you eat them helps to remove any bacteria, fungi or pesticides that may be on the skin of the grapes. Not only do grapes pick up contaminants from where it was grown, they can also pick up contaminants while being transported across long distances. It is best to buy locally grown grapes for this reason.
Cool Water Rinse
Grapes should be washed right before use. Washing them and then storing them in the refrigerator may allow bacteria to grow and rot to set in. Before you begin, first wash your hands so that any bacteria or dirt on your hands is not transferred onto the grapes you are cleaning. Place grapes in a colander or hold them in your hand. Wash them under cool water. Remove any grapes that are broken open or show signs of mold or rot. If you are canning or freezing the grapes, select only the healthiest looking grapes for preservation.
References and ResourcesUtah State University Cooperative Extension: Grapes
Colorado State University: Guide to Washing Fresh Produce