Agar is a gelatinous substance mainly composed of agarose and agaropectin, which can be extracted from the cell walls of algae such as Gelidium and Gracilaria (Ogonori) in Rhodophyta. The gel formation and melting process of agar are based on hydrogen bonding and belong to physical gels, so the gelation process is reversible. With its unique physicochemical properties, agar is widely used in food additives, plant tissue culture, microbial medium preparation, fingerprint development, and medical-related fields.