[jiang]

Dear teachers,

Could you please kindly analyze the grammar of the following sentence:

When the bottle had been uncorked and the wine poured out, like sunlight I watched it go down.
The complete structure of the underlined part should be "and the wine had been poured out", which is predicate. My question is:
Since "had been " is omitted can I still say it is "predicate" ? If I can't then could you please explain what's the function of it?

Looking forward to hearing from you.
Thank you in advance.

Jiang