The most common and most likely answer to this crossword clue is the 8 plus 5 letter word DEMERARA SUGAR
I've seen this crossword clue in The Daily Telegraph
D
E
M
E
R
A
R
A
S
U
G
A
R
More clues leading to the result DEMERARA SUGAR
Buddy explains!

The straight part
We know that "Ingredient" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ingredient = demerara sugar.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.