The most common and most likely answer to this crossword clue is the 4 plus 5 letter word MILK STOUT
M
I
L
K
S
T
O
U
T
More clues leading to the result MILK STOUT
Buddy explains!

The straight part
We know that "Sweetened beer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sweetened beer = milk stout.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.