agars

Agars, or agar-agar, are gelatinous polysaccharides derived from red seaweed, primarily from genera such as Gelidium and Gracilaria. They are used as gelling agents in food and as solidifying media in microbiology. The term “agars” may refer to agar-based products in general or to different varieties of agar.

Agar is produced by boiling seaweed in water to extract the soluble polysaccharides, filtering, and drying the resulting gel to form a powder. It consists mainly of two polymers, agarose and agaropectin. Agarose largely determines the gel-forming ability, while agaropectin influences texture and color. The material is resistant to degradation by most common bacteria and enzymes, making it suitable for thermal processing and long-term stability.

In its physical behavior, agar dissolves in hot water to produce a clear solution that gelates on cooling. Laboratory media typically use about 1.5% agar by weight to create a firm, semi-solid surface on petri dishes or tubes. The gelation temperature for common preparations occurs around 32–40°C, while the melting temperature ranges from about 85–90°C, depending on concentration and formulation. Agar is pH-tolerant and stable over a wide range of temperatures, which makes it versatile for various applications.

Uses of agars span several domains. In microbiology, agar-based media provide a solid, porous matrix that supports the growth of microorganisms while enabling colony isolation and observation. In molecular biology, agarose—a derivative of agar—is used to create gels for electrophoretic separation of nucleic acids. In food and culinary contexts, agar is used as a vegetarian gelling agent in desserts, jellies, and dairy substitutes.