A necessity in winemaking (4)
I believe the answer is:
must
'a necessity' is the definition.
(I know that must is a type of essential)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for must that I've seen before include "Smell of dampness or staleness" , "The imperative for mould" , "Fermenting grape juice" , "Unfermented wine" , "Make off with (plane)" .)