Open level country, we hear, for producing sparkling wine (9)
I believe the answer is:
champagne
'sparkling wine' is the definition.
(champagne is a kind of sparkling wine)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for champagne that I've seen before include "French wine district" , "Celebratory drink" , "French 'sparkler'" , "the stuff of success?" , "Sparking drink" .)