Mashed barley left out as herbal drink (5)
I believe the answer is:
yerba
'herbal drink' is the definition.
(I've seen this before)
'mashed barley left out' is the wordplay.
'mashed' indicates an anagram.
'left' becomes 'l' (common abbreviation).
'out' indicates named letters should be taken away.
'barley' with 'l' taken out is 'barey'.
'barey' anagrammed gives 'YERBA'.
'as' is the link.
(Other definitions for yerba that I've seen before include "Herbal drink" , "Paraguay tea" , "Evergreen S American tree, also called mate" , "--- Mate is a type of tea" , "South American infusion" .)