The most common and most likely answer to this crossword clue is the 13 letter word LIEBFRAUMILCH
I've seen this crossword clue in The Daily Telegraph
L
I
E
B
F
R
A
U
M
I
L
C
H
Buddy explains!
The straight part
We know that "Pour this into glasses" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pour this into glasses = liebfraumilch.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.