Hard to get one's teeth into side of cheese with mushy whey (5)
I believe the answer is:
Here is my best explanation:
'hard' is the definition.
I cannot understand how the remainder of the clue works.
(Other definitions for chewy that I've seen before include "Soft and sticky (to eat)", "Like toffee", "hard to eat", "Hard to eat", "Requiring mastication, like toffee say", "With a texture like toffee", "Tough to masticate" and "Taking much mastication".)