Agar-agar (usually shortened to agar) is a naturally-occuring gelling agent traditionally derived from various species of seaweed found in the Asian seas. It is used in many food products (mostly jams and jellies), as a thickening and emulsifying agent, as well as serving in laboratories as a culture medium for bacteria, yeast, and molds, as a gel base for electrophoresis and similar procedures and a host of other uses.
Laboratory-grade agar-agar is generally shipped as a creamy-yellow powder or small yellowish bars, while food-grade agar-agar is usually sold as flakes or long strips or bars. Unflavored agar is rich in iodine and other trace minerals, and has mildly laxative properties, due to its high fiber content (over 80%).
To cook, agar-agar (flaked or powdered, 2 teaspoons of powder or 2 tablespoons of flakes per 600 ml of water) is dissolved in boiling water and simmered for 5-10 minutes; bars generally have to be soaked before boiling for an additional 5 minutes. Unlike gelatine, it will set at room temperature, and does not require refrigeration, except for storage. It can also be reboiled and re-set if needed.
Several species of seaweed provide agar-agar; the best originated in Japan (known as Kanten) where it is produced from a combination of Gelidium and Euchema algae. The raw seaweed is cooked and pressed, then freeze-dried to form bars, which can either be shipped as-is, or flaked for packing. Laboratory-grade agar is cheaper, as it is chemically processed and bleached to remove the natural color and flavor.
The bulk of commercial agar-agar is produced in other countries, including Indonesia and Malaysia (mostly from Gelidium and Gracillaria algae), the Philippines (various species of Gelidium and Euchema), as well as India and Ceylon (traditionally, Gracillaria lichenoides, known locally as agal-agal). A Chinese variety, from Gigartina speciosa is sometimes used in native dishes, and was once thought to be the key ingredient in bird's-nest soup. Macassar agar-agar, from Borneo and the Celebes Sea, is derived from Euchema Spinolum tainted with sea salt.
B & V Agar Agar (http://www.agar.com/agaragar.htm)
The Vegetarian Society UK (http://www.vegsoc.org/info/gelling.html)
Indoking Agar (http://www.indoking.com/Index-ia.htm)