Let beer on top ferment. It gets the cap off (6-6)

I believe the answer is:

bottle-opener

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'it gets the cap off' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'let beer on top ferment' is the wordplay.
'ferment' indicates an anagram (I've seen 'fermented' mean this).
'let'+'beer'+'on'+'top'='letbeerontop'
'letbeerontop' anagrammed gives 'BOTTLE-OPENER'.

Can you help me to learn more?

(Another definition for bottle-opener that I've seen is " Device for removing caps and corks".)

I've seen this clue in The Globe and Mail.

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