Spinach also has disadvantages. Because it contains more oxalic acid, it tastes a little astringent. Oxalic acid is easy to combine with calcium in food to form insoluble calcium oxalate, which hinders the absorption of calcium by human body. Eating foods with high oxalic acid content for a long time is easy to produce kidney calculi. Therefore, it is best to blanch spinach with water before eating, and 80% oxalic acid in spinach can be removed after blanching. But the blanching time should not be too long, otherwise it will reduce the vitamin content in spinach. The blanched spinach not only loses little nutrients, but also has a good taste.