Dashi and umami

Kombu is harvested mainly along the coasts of Hokkaido, and different varieties are prized for different purposes: ma-kombu from the Hakodate area for its sweet, clear stock, rishiri-kombu for the delicate broths of Kyoto, and rausu-kombu for richness. Katsuobushi is made by filleting, simmering, smoking and drying skipjack tuna until it is as hard as wood; the best grades are also cultured with mould. Makurazaki in Kagoshima Prefecture and Yaizu in Shizuoka Prefecture are the main production centres.

Ichiban dashi, the 'first dashi', is a short extraction of kombu and katsuobushi used where clarity and aroma matter most, such as in clear soups (suimono). Niban dashi reuses the same ingredients for a stronger, cloudier stock for simmering and miso soup. Kombu dashi alone, or kombu with shiitake, gives a vegetarian stock used in shōjin ryōri.

Today many households use granulated instant dashi or dashi packs, but restaurants and careful home cooks still make it fresh each day.

Japan's two great culinary centres differ in their stock. In the Kansai region around Kyoto and Osaka, dashi leans on kombu and is seasoned with pale usukuchi soy sauce, giving light-coloured broths with a clear kelp taste. In the Kanto region around Tokyo, katsuobushi dominates and darker koikuchi soy sauce is used, so noodle broths there look much darker.

The Kansai preference goes back to the Edo-period kombu trade: Kitamae-bune cargo ships carried kelp from Hokkaido along the Sea of Japan coast to Osaka, and the trade reached as far as Toyama and the Ryukyu Kingdom. Both Toyama and Okinawa still use kombu heavily in their cooking.

In 1908 Ikeda Kikunae, a chemistry professor at Tokyo Imperial University, isolated glutamic acid from kombu and identified it as the source of the taste he called umami, from umai (delicious). He patented a method of producing monosodium glutamate, which became a seasoning sold worldwide. His student Kodama Shintarō identified inosinate in katsuobushi in 1913, and Kuninaka Akira later found guanylate in dried shiitake.

For decades umami was not widely accepted in Western science as a basic taste. The identification of specific taste receptors for glutamate around the turn of the twenty-first century settled the question, and umami is now recognised alongside sweet, sour, salty and bitter.