Japan — Welsh onion (Allium fistulosum) cultivation from ancient times; regional variety development through Edo period; the shiro/ao negi divide correlates with the regional flavour philosophies of Kanto and Kansai
Negi (ネギ, Allium fistulosum, Japanese bunching onion/Welsh onion) is one of the most versatile and culturally embedded ingredients in Japanese cooking — appearing as an aromatic base in every category of preparation. Two main varieties exist in Japanese cooking: Shiro negi (white negi, 白ネギ) from Kanto — thick, the majority of the stalk is pale white with minimal green, sweet when grilled or braised, pungent when raw; and Ao negi (green negi, 青ネギ) from Kansai — thin, completely green, milder, used primarily as a fresh garnish scattered over soups, noodles, and rice bowls. The regional divide in negi preference mirrors the Kanto-Kansai culinary divide — Tokyo cooks default to thick white negi, Osaka to thin green negi.
Raw: sharp, pungent, allium heat; grilled: extraordinarily sweet, yielding, charred exterior giving way to silky interior; as garnish: fresh sharp onion note that lifts the surrounding preparation
Shiro negi: the white section only is used for most preparations; the blue-green section is tougher and is used in stock or discarded. Cut diagonally (nanamegiri) for nabe and grilled preparations; julienned into thin threads (shiraganegi) for sashimi garnish; and finely sliced rounds for soup and noodle topping. For grilled negi: char over direct fire until the outer layer is blackened, then peel to reveal the sweet, yielding interior — a transformation of character impossible through any other cooking method. Ao negi is always used raw, sliced thin, added at the final moment.
The most spectacular negi preparation: Kyoto fukuro negi, a regional white negi from Kyoto that is slightly more delicate than standard shiro negi. Grill whole until completely charred on the outside, split, and serve as a side dish with miso — the interior is astoundingly sweet and silky. For shiraganegi garnish: julienne the white section paper-thin, submerge in ice water for 5 minutes — the threads curl into beautiful spirals. Drain and dry before using. The negi in a proper ramen topping is sliced on a sharp diagonal to expose maximum surface area to the hot broth.
Using the green section of shiro negi where the white section is specified — the green section is significantly more pungent and tough. Not soaking shiraganegi threads in cold water after julienning — rinsed and chilled, they curl elegantly and lose excess pungency. Using ao negi as a substitute for shiro negi in preparations requiring grilling — ao negi has insufficient mass for the char-and-reveal technique.
Tsuji, Shizuo — Japanese Cooking: A Simple Art; Hosking, Richard — A Dictionary of Japanese Food