Rock singer guzzling at intervals plain white wine (8)
I believe the answer is:
riesling
'white wine' is the definition.
(Riesling is an example)
'rock singer guzzling at intervals plain' is the wordplay.
'rock' indicates an anagram (the solver must 'rock' the letters around).
'guzzling' indicates putting letters inside (I've seen this in other clues).
'at intervals' indicates alternate letters (letters are taken at regular intervals).
The alternating letters of 'plain' are 'li'.
'singer' is an anagram of 'riesng'.
'riesng' going around 'li' is 'RIESLING'.
(Other definitions for riesling that I've seen before include "Sir Ingle makes wine from this grape" , "Fragrant white wine from the Rhine valley or from California" , "Aromatic white wine from the Rhine valley" , "Strange wine for Sir Ingle" , "Gin riles the wine" .)