Fibre in beans is alarming (5)
I believe the answer is:
sisal
'fibre' is the definition.
(sisal is a kind of fibre)
'in beans is alarming' is the wordplay.
'in' says the answer is hidden in the clue.
'SISAL' is hidden in the letters of 'beans is alarming'.
(Other definitions for sisal that I've seen before include "Fibre-yielding plant" , "Agave cultivated for its fibre" , "Fibre from agave plant" , "Strong rope fibre" , "Fibrous plant used for rope" .)