Agar

Agar is a complex combination of two different polysaccharides, agarose and agaropectin, which are extracted by cooking red algae and then freeze-drying the filtered, warm liquid. Commercially, it is sold in the form of a powder, granules, or thin filaments and often serves as a vegetarian substitute for gelatin. Agar is insoluble in cold water, but dissolves readily in boiling water and can be used to form thermoreversible gels. To form gels, the agar is first softened in cold water, which is then brought to the boiling point and subsequently cooled to below about 100°F (38°C). Once set, however, the gel will not melt again before it is heated to at least 185°F (85°C). Stirring can change solid gels made with agar into liquid ones, but they do not withstand freezing. In contrast to gels made with gelatin, those made with agar are less sticky; have a clean, crisp mouthfeel; and do not melt in the mouth but keep their shape and stay firm. This latter property can be exploited to make pieces of gel that can be incorporated into a warm dish to add structural interest and release additional taste substances. Agar also forms gels at much lower concentrations than gelatin does, having the formidable capacity to set mixtures of up to 99.5 percent water. But one drawback with using agar, as compared with pectin and gelatin, is that the gels are less clear, have a coarser texture, and crumble easily. Unlike alginate, agar is not affected to any great extent by the presence of ions and it tolerates an acidic environment.