Kombu, edible kelp (a type of seaweed), is used a lot in Japanese cuisine and forms the basis of the seasoning in various dishes.
Oboro kombu (shaven kelp) is a variety of kombu, that has been produced in the city of Sakai, Ōsaka Prefecture, for centuries. Due to its proximity to Osaka harbour and its 600-year history of producing forged knives, Sakai provided an ideal basis for the manufacture of shaven kelp, which relies on the ability of skilled craftspeople who manually shave the kombu into paper-thin slivers with a thickness of less than 0.05 mm.
Harvested in Hokkaidō, the northernmost of Japan's main islands, kombu was historically brought to Sakai via ship through a route known as the ‘Kombu Road’.
Hokkaidō, which is surrounded by cold, nutrient-rich currents, produces a wide variety of flavourful kombu. Varieties include rishiri kombu (harvested in northern Hokkaido), rausu and naga kombu (both harvested in eastern Hokkaido), hidaka and ma kombu (southern Hokkaido) and hosome kombu (western Hokkaido).
All varieties have distinct features. While rishiri kombu produces a very clear broth that is used in kaiseki-style cuisine, rausu kombu makes a richer, umami-flavoured broth. And while the rausu variety is harvested in small quantities, which makes it a more expensive product, naga kombu grows in long sheets and can be harvested in large amounts. Ma kombu is the variety used for oboro kombu.
In cooking, kombu is mainly used in two ways. It can either be used to make broth (by boiling kombu with water, sometimes adding other ingredients such as katsuobushi bonito flakes or shiitake mushrooms), or it can be processed and eaten by itself.
Oboro kombu is one way of preparing kelp for consumption. It originated in Sakai, a city that has long been famous for its production of sharp kitchen knives and its skilled craftspeople. The process has remained much the same through the ages.
Dried sheets of kombu are delivered from Hokkaido to Sakai, where the processing begins by soaking the kombu in vinegar, usually for between 30 seconds and one minute, depending on the season and the condition of the kombu. The sheets are then removed from the vinegar and left to rest overnight. Before the shaving begins, sand and black skin are removed from each individual sheet.
Special knives which are extremely sharp and angled at the blade’s edge are used to shave the kombu. Skilled craftspeople shave the sheets on alternating sides.
At the end of the process, the white core of the sheet, known as shiroita kombu, remains. It can be seasoned with sweet vinegar and used in pressed sushi, a popular Osaka dish. Oboro kombu can be used as a topping for udon or wrapped around an onigiri rice ball.
