Wine expert at rest is drunk (6)
I believe the answer is:
taster
'wine expert' is the definition.
(I've seen this in another clue)
'at rest is drunk' is the wordplay.
'at' becomes 'ta' (I can't explain this - if you can you should give a lot more credence to this answer).
'is drunk' indicates anagramming the letters.
'rest' with letters rearranged gives 'ster'.
'ta'+'ster'='TASTER'
Can you help me to learn more?
(Other definitions for taster that I've seen before include "Winery worker" , "Small sample" , "Art set (anag.)" , "Sampler of food" , "A professional savourer, of wine or tea" .)