A scientist's wife suggested the seaweed jelly that transformed microbiology
In 1882 Walther Hesse, working in Robert Koch's lab, needed a better surface for growing bacteria. His wife Fanny suggested agar, a jelly made from seaweed and long used in Asian desserts. It stays solid at body temperature where gelatin melts, and it quickly became the base of the Petri dish.
Agar comes from the cell walls of certain red seaweeds, mainly Gracilaria and the Gelidium family, and is released by boiling. It combines two sugars: agarose, about 70 per cent, and agaropectin, which is stripped out in food-grade agar. Its secret is hysteresis: it sets into a gel somewhere around 32 to 42 degrees Celsius but does not melt again until about 85. That gap lets labs incubate microbes near 37 degrees without their growing surface turning to soup.
Its kitchen history is much older. Japanese legend credits an innkeeper near Kyoto, Mino Tarozaemon, with discovering the production method in 1658 after throwing out leftover seaweed soup that froze overnight and dried in the sun into a whiter jelly. Filipinos ate gulaman jellies for centuries, recorded in a Tagalog dictionary of 1754, and 19th-century British Malaya shipped dried seaweed to China in bulk. The word itself comes from the Malay agar-agar, which Europeans adopted in the East Indies; the French chemist Anselme Payen first analysed it chemically in 1859.
Science changed the industry. Japan made most of the world's agar until the Second World War cut supplies and forced other nations to start their own. Output rose from about 2,500 tons a year around the war to some 10,000 tons by the mid-1970s, and has fluctuated since as seaweed stocks were strained.
In food it acts as a plant-based stand-in for gelatin and a thickener for soups, jams and ice cream, and brewers use it to clarify beer. It is about 80 per cent fibre and triples in size as it soaks up water, which fuelled a kanten diet craze in Asia. It sets Japanese anmitsu and mizu yokan, Vietnamese layered thach and Filipino halo-halo.
Source: Agar
