Answer:

sourest

Answer	Crossword Clue
SOUREST	Most ill-tempered
SOUREST	Produces the biggest pucker
SOUREST	Tart to the max

SOUREST	Most bitter
SOUREST	Most tart
SOUREST	Most off-pitch
SOUREST	Most vinegary
SOUREST	Most like a lemon
SOUREST	Most unpleasant
SOUREST	Most fermented.
SOUREST	Most peevish

SOUREST	Most kumquat-esque

Crossword

a puzzle consisting of a grid of squares and blanks into which words crossing vertically and horizontally are written according to clues.