Spooner's tending barbeques in grain factories (8,5)

I believe the answer is:

grinding mills

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'spooner's tending barbeques' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'grain factories' is the wordplay.
'grain' becomes 'grinding' (I can't explain this - if you can you should believe this answer much more).
'factories' becomes 'mills' ('mill' can be a synonym of 'factory').
'grinding'+'mills'='GRINDING MILLS'

'in' is the link.

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I've seen this clue in the Sydney Morning Herald.

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