Lose track of mass whisky producer (6)
I believe the answer is:
mislay
'lose track of' is the definition.
(I've seen this before)
'mass whisky producer' is the wordplay.
'mass' becomes 'm' (symbol used in Physics e.g. f=ma).
'whisky producer' becomes 'islay' (the island of Islay produces whisky).
'm'+'islay'='MISLAY'
(Other definitions for mislay that I've seen before include "Set in wrong location" , "Lose (an item)" , "Put in wrong place, lose temporarily" , "Put (something) where it can't be found" , "Temporarily not find" .)