Agar agar is a kind of polysaccharides distilled from agar, Gracilaria and other red alga plants. Its main components are the sulphate of poly-galactose. The agar agar products are strip-shaped or powdery. The most useful feature of agar agar is the big difference between its freezing point and melting point. In the water, agar agar melts only when heated to 95 degrees and solidifies only after the temperature decreases to 40 degrees, so agar agar is the best coagulant for preparation solid medium. The agar solid medium can be cultured at high temperature and will not melt. The inoculation before solidification will not burn the culture itself to death. Therefore, agar agar is the most widely used coagulant in preparing various biological mediums. The agar agar concentration is usually 1-1.5% the liquid medium.
In food industry, agar agar has unique and useful properties, such as coagulability, stability and physical and chemical property of forming complex with other materials.