What does the cryptic crossword clue "Could this drink be nastier? (7)" mean?

The definition is "be nastier?". The wordplay uses an anagram. anagram of NASTIER ("nastier?") [anagram: "Could"] = RETSINA The answer is RETSINA.

Could this drink be nastier? (7)

Independent Cryptic #1806 | 7 Down | 2024-10-06 flower