Beers used in cocktails? (7)

I believe the answer is:

bitters

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'beers' is the definition.
(I have seen 'Traditional beers ' mean 'bitters' so perhaps 'beers' could also mean 'bitters')

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for bitters that I've seen before include "Sharp-tasting additive" , "Flavoured alcoholic liquor" , "Traditional beers" , "Angostura - - , a cocktail flavouring" .)

I've seen this clue in The Irish Independent.

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