If the grapes are too sour, you can wash the grapes, throw them into a prepared bottle, poke the grapes with a knife to break the skin, put some sugar in it, and seal it . Soak in this way for 2 weeks. When the color of the skin becomes lighter and the color of the water in the bottle becomes darker, it becomes wine and you can drink it. This tastes great and retains the nutrients in the grapes.