Strain composed by chap is bitter (10)
I believe the answer is:
astringent
'is bitter' is the definition.
(I've seen this before)
'strain composed by chap' is the wordplay.
'composed' is an anagram indicator.
'by' says to put letters next to each other.
'chap' becomes 'gent' (both can mean a man).
'strain' with letters rearranged gives 'astrin'.
'astrin'+'gent'='ASTRINGENT'
(Other definitions for astringent that I've seen before include "Scathing" , "piercing" , "Styptic" , "description of wine?" , "Lotion" .)