What does the cryptic crossword clue "What's milky when shaken? Drink from barley (4,6)" mean?

The wordplay uses an anagram. anagram of WHAT'S + MILKY = MALT WHISKY The answer is MALT WHISKY.

What's milky when shaken? Drink from barley (4,6)

Times Cryptic #28884 | 1 Across | 2024-04-06 flower