Two firms onto a drink from beans (5)
I believe the answer is:
cocoa
'drink from beans' is the definition.
(I've seen this before)
'two firms onto a' is the wordplay.
'two firms' can mean two substitutions for 'firm'.
'firm' becomes 'co' (a firm is a company).
'firm' becomes 'co' (a firm is a company).
'onto' means one lot of letters go next to another.
'co'+'co'+'a'='COCOA'
(Other definitions for cocoa that I've seen before include "Evening drink taken in rococo amphitheatre" , "Medium to dark brown" , "Late-night drink" , "Lightish brown colour of a drink" , "Main constituent of chocolate" .)