Grimchi is a foodstuff known and mainly avoided in parts of the Agatean Empire. It is created by taking significantly large amounts of cabbage (the Jolly Giant variety, for preference, although the Choi Champion is also a recognised variety), macerating it, adding pickling vinegar and the very special Seven Spice Black Powder whose precise chemical composition is a closely-guarded secret known only to grimchi-adepts back home. The ingredients are then thoroughly stirred, placed into specially reinforced fermentation vats, and, once firmly sealed, buried in the earth for seven years. In very deep pits.
The B'Hang family from Agatea moved to the Central Continent, having heard wonderful travellers' tales of a land so abundant in cabbage that it grew almost wild for hundreds of miles in every direction. They arrived to discover the wild and exaggerated tales brought back by a previous intrepid explorer were, in fact, understated, if anything. In a joyous sense of having arrived in Heaven without actually having died first, the B'Hang family established a grimchi-making enterprise that they envisaged would make them rich for life, once they began exporting it Home. And who knows, the local white ghosts, who, get this, could only think of boiling the stuff and eating it practically fresh, yuk, might get a taste for it too.
Alas, the B'Hang family were prepared neither for the overwhelming quantity of cabbage nor familiar with the peculiarities of Central Continent brassica. Having established seven huge, custom-made, ceramic fermentation vats and having buried them deeply, they sat back to wait out the necessary years until the grimchi had fermented to perfection.
They did not wait very long.
A series of massive, destructive, explosions rent the air. Ceramic shrapnel scythed down everything it touched. Great boluses of foul-smelling sludge contaminated everything it touched for a radius of some miles from Ground Zero. Fearing they would be blamed for the catastrophe, the B'Hang family moved very quickly away and are lost to history. The population of Seven Bangs has since stabilised at 27, and the railway engineers established a line through the area, threading the railway between seven huge craters, with some caution. Seven Bangs Halt serves the residual cabbage-farming industry, which is yet to recover. Travelling out of Ankh-Morpork, the preceding station is Upper Feltwhistle and the next stop is Fratchwood.
This is the first Discworld mention of Korea, or a Korean-like country. Kimchi is a Korean dish of lacto-fermented cabbage, similar to sauerkraut. Its strong taste is not to everybody's liking; it's like Marmite. You love it or hate it. Pak Choi is a Chinese cabbage variety.