Grapes are a rich source of proteins, vitamin K, vitamin A, potassium manganese and iron. Grapes are known for their cleansing quality and helps in cleansing the liver and removing uric acid. Red grapes also contain resveratrol, a phytochemical that protects the body from a number of chronic diseases. The powerful flavonoids in grapes protect the heart by preventing formation of plaque in artery walls and help the body to fight the effects of harmful free radicals. The best way to juice grapes is to wash and drop them in the juicer along with the stems.