A confusing "which"

Hi guys,

I am not quite sure what the following sentence really means:

When he was alone, he drank gin rather than wine, which he preferred.

A. He preferred wine.
B. He preferred drinking gin rather than wine.

In other words, does "which" stand for "wine" that immediately precedes it, or the whole sentence preceding it, as in, "He broke the vase, which pissed his father off?"

Thank you very much!

BTW, here is the context:

Gabriel J. Utterson, a London lawyer, had a
rugged face that never was lit by a smile. An
unemotional bachelor, he was reserved and brief
in his speech. He was tall, slender, dusty, and
dreary, yet somehow lovable. At a gathering of
friends, and when the wine suited his taste,
something highly human shone from his eyes—
something that never found its way into his talk
but showed in his after-dinner face and, more
often and clearly, in his actions. He was austere
with himself. When he was alone, he drank gin
rather than wine, which he preferred. Although
he enjoyed theater, he hadn’t gone to a theater
for twenty years.