Firm needing endless fuel to produce drink (5)
I believe the answer is:
cocoa
'drink' is the definition.
(I know that cocoa is a drink)
'firm needing endless fuel' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'needing' means one lot of letters go next to another.
'endless' means to remove the last letter.
'fuel' becomes 'coal' (coal is a kind of fuel).
'coal' with its final letter taken away is 'coa'.
'co'+'coa'='COCOA'
'to produce' is the link.
(Other definitions for cocoa that I've seen before include "Chocolate-like drink" , "Hot bedtime drink" , "Evening drink taken in rococo amphitheatre" , "Chocolaty drink" , "Hot beverage" .)