Now that it's crab season, try this Eastern Chinese dipping sauce, loaded with fresh ginger and vinegar. Put the live crab in a steamer over rapidly boiling water; cover and steam for 15 minutes. Meanwhile, mix the remaining ingredients thoroughly until the sugar dissolves. Divide sauce among 2 to 4 dip bowls, depending on the number of diners. Serve with the steamed crab. NOTE: Chopped fresh coriander may be added, if desired. By Bruce Cost, San Francisco Chronicle, 11/16/88.