The grapes are soaked in baking soda for 10 minute, and then washed for 2 minutes. Baking soda, that is, sodium bicarbonate, commonly known as baking soda, baking soda powder and sodium bicarbonate, is a white fine crystal, and its solubility in water is less than that of sodium carbonate. This is an industrial chemical, which may be toxic.

Solids above 50℃ begin to decompose gradually to produce sodium carbonate, carbon dioxide and water, and completely decompose at 440℃. Sodium bicarbonate is an acid salt formed by neutralization of strong alkali and weak acid, which is weakly alkaline when dissolved in water. This characteristic can make it a leavening agent in food production. Sodium carbonate will remain after the action of sodium bicarbonate, and excessive use will make the finished product have an alkaline taste.