Agar

Agar is a gelatinous polysaccharide derived from certain species of red algae, notably Gelidium and Gracilaria. It consists mainly of two components: agarose, a neutral linear polymer, and agaropectin, a charged, branched heteropolysaccharide. Agar forms a thermally reversible gel that can hold water and nutrients, making it useful in a wide range of applications.

In its physical form, agar dissolves when heated in water and forms a gel as it cools. The gel is stable over a broad temperature range and, unlike many other gels, does not melt until about 85–90°C, with gelling occurring around 32–40°C depending on concentration and additives. Because it is not readily digested by humans, agar acts as dietary fiber in foods and is valued as a neutral thickener and stabilizer.

Agar has two major uses. In microbiology, it is the standard solidifying agent for culture media, enabling the growth and isolation of microorganisms in petri dishes, tubes, and slants. In molecular biology, agarose, a purified fraction of agar, is used to form gels for DNA and RNA electrophoresis, where molecules separate by size. In the food industry, agar is used as a vegan alternative to gelatin for desserts, jellies, puddings, and thickened dairy or meat products, due to its high gel strength and heat stability.

Preparation involves extracting the polysaccharide from seaweed with hot water, purifying, and drying to a powder. It is generally regarded as safe for consumption, though some individuals may have sensitivities.