Part of Miss Muffet's meal (4)
I believe the answer is:
whey
'part of miss muffet's meal' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for whey that I've seen before include "Part of 26 Across" , "Milk serum" , "Watery residue of milk" , "Part of Miss Muffet's diet" , "Watery remains after the curds are separated in milk" .)