How to fry in a jug? (4)

I believe the answer is:

stir

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'a jug?' is the definition.
(both are slang for prison)

I cannot understand how the rest of the clue works.

(Other definitions for stir that I've seen before include "Awaken" , "Stimulate; prison" , "Excite emotionally" , "Excitement" , "Uproar" .)

I've seen this clue in the Evening Standard.

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