Certain alcoholic beverage kept as standard (8)
I believe the answer is:
measured
'certain' is the definition.
(thesaurus)
'alcoholic beverage kept as standard' is the wordplay.
'alcoholic beverage' becomes 'mead' (mead is a kind of alcoholic beverage).
'kept' is an insertion indicator.
'as standard' becomes 'sure' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'mead' enclosing 'sure' is 'MEASURED'.
Can you help me to learn more?
(Other definitions for measured that I've seen before include "Rhythmical, regular in movement" , "Found the size or quantity of something - using tape or ruler" , "Metered" , "Calculated, quantified" , "Deliberate, restrained" .)