Ungrammatical? "She belted most of a bottle of wine down before dinner had even begun."

Peaceblinkfriend

from what I have learned about Past Perfect, it seems to me that it is ungrammatical that 'had even begun' is in Past Perfect tense.

No.  It's grammatically correct to use the past perfect tense when the before clause indicates that an event has not yet happened at the time of the main clause, but suggesting that perhaps the event was going to happen.  This construction can (correctly) give the impression that events occurred in the reverse order from what was expected, customary, or desirable.  (In the case at hand, the writer expected that the dinner would begin first and the wine drinking would take place later.)

She belted down the wine before the dinner had begun

= The dinner had not yet begun [when / at the time] she belted down the wine. 

See Re: past perfect in dependent clause

CJ 

 

Copying myself from another thread: 

Iamnewbie

Isn't it a Subjunctive Mood, is it?

Yes, you can look at it that way and that's a nice justification. CJ's example: 

Mozart died before he had completed the Requiem Mass.

can  be read as:

 Mozart died before THE HYPOTHETICAL ACTION IN WHICH he would have completed the Requiem Mass.