When vinegar is not suitable for cooking, if vinegar seasoning is added, the vegetables will lose their bright green color and affect their sensory properties. This is because chlorophyll in vegetables is extremely unstable when heated under acidic conditions, and magnesium ions in its molecules can be replaced by hydrogen ions in acids to form pheophytin. In addition, green vegetables are rich in vitamin C, which is prone to oxidative failure under alkaline conditions. Therefore, do not use vinegar when cooking, but fry quickly under neutral conditions.