Place the stock and ginger in a large saucepan and bring to the boil. Add the corn and simmer uncovered for 10 minutes. Blend the cornflour in a small bowl, with the soy sauce and Chinese rice wine.
Stir into the stock and season with freshly ground black pepper, to taste. Add the crab meat and simmer for 5 minutes, then stir in the sesame oil, spring onions and coriander. Cover with a lid and leave to stand for 1 minute. Serve immediately.