Tasters in a mixture masking new pungency (8)
I believe the answer is:
tartness
'pungency' is the definition.
(having an acid or tart flavour)
'tasters in a mixture masking new' is the wordplay.
'in a mixture' indicates an anagram.
'masking' is an insertion indicator (inserted letters are covered up or masked).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'tasters' is an anagram of 'tartess'.
'tartess' enclosing 'n' is 'TARTNESS'.
(Other definitions for tartness that I've seen before include "pungency" , "bitter taste" .)