Rinse raw pearl barley; Soak it in water for 3 hours; Remove and drain it.
Rinse dried Chinese yam; Soak it in water for 1 hour; Remove and drain it.
Rinse, drain and slice ginger.
Remove husks of corn; Rinse and drain it; Cut it into sections.
Rinse, drain and peel a carrot; Trim an half inch off its top and the bottom; Cut it into chunks.
Rinse, drain and cut chayote into chunks.
Rinse pork bones; Pat-dry them with kitchen paper; Cut them into chunks.
Fill a stockpot with 2.5L water; Bring to the boil over a high heat;
Add the pork bones and the ginger; Cook over a high heat for 5 minutes;
Remove the ginger with a wire skimmer; Scoop scum off with a perforated spoon and discard; Add all the remaining ingredients and bring to the boil over a high heat again; Turn to a low heat; Cover the pot with its lid; Cook over a low heat for 2 hours; Stir seasonings into the soup; Turn off the heat; Arrange the soup in a serving round terracotta pot; Ready to serve.