Refrigeration spoils oldest cargo (4,7)
I believe the answer is:
cold storage
'refrigeration' is the definition.
(I've seen this before)
'spoils oldest cargo' is the wordplay.
'spoils' indicates anagramming the letters.
'oldest'+'cargo'='oldestcargo'
'oldestcargo' is an anagram of 'COLD-STORAGE'.
(Other definitions for cold storage that I've seen before include "Preservation at low temperatures" , "refrigerator" , "Being on ice" , "State of temporary suspension" , "State of abeyance - refrigeration" .)