Acidity regulators are substances used to maintain or change the acidity of the food. The lye added to sour noodles is an acidity regulator. It is mainly used to control the acidifying agents, alkalis, and salts with a buffering effect needed for the food. Each acidity regulator has a different acidity level and acidity characteristics. There are 17 types of acidity regulators allowed, including citric acid, potassium citrate, lactic acid, and tartaric acid, of which citric acid is a widely used acidity regulator.