Food certain to go off after a year (5,4)

I believe the answer is:

patna rice

'food' is the definition.
(type of rice)

'certain to go off after a year' is the wordplay.
'to go off' indicates an anagram.
'after' means one lot of letters go next to another.
'a year' becomes 'pa' (per annum).
'certain' anagrammed gives 'tnarice'.
'tnarice' after 'pa' is 'PATNA RICE'.

I've seen this clue in The Times.

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