Using unwashed grapes for winemaking is a time-honored tradition. However, washing the grapes offers several advantages. It removes pesticides, insects, and may reduce the chemicals that could lead your wine to become vinegar rather than wine. The process may even be used to remove bad grapes, which would have a negative impact on the flavor of the wine. While you may be able to argue the flavor of wine from unwashed grapes is desirable, it's hard to say anything positive about having pesticide residue in your wine.
Do you make wine? If so, do you wash your grapes or leave them as-is? Do you have an opinion about whether or not grapes should be washed? If so, post a response.