Regularly drained cocktails, white wines (9)

I believe the answer is:

rieslings

I'm a little stuck... Click here to teach me more about this clue!

'white wines' is the definition.
(Riesling is an example)

'regularly drained cocktails' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'cocktails' becomes 'slings' (I am not sure about this - if you are sure you should believe this answer much more).
The alternating letters of 'drained' are 'rie'.
'rie'+'slings'='RIESLINGS'

Can you help me to learn more?

I've seen this clue in The Independent.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.