Bring the stock to a boil in a pan. Meanwhile stand the sweetcorn on a board and slice away the kernels with a large sharp knife. Add the sweetcorn to the stock and simmer for 5 minutes.
Check the crabmeat for any residual small pieces of shell, keeping the meat in the largest pieces possible.
Mix the cornflour to a smooth paste with a little cold water then stir it into the soup. Simmer for 2 minutes.
Add the crabmeat, ginger, spring onions, soy sauce and rice wine. Season to taste. Simmer for a minute.
Stir well then remove spoon and slowly trickle in the beaten egg white so it forms long thin strands. Simmer for 30 seconds then serve immediately.