Mature Brie open and denied all outsiders (5)

I believe the answer is:

ripen

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'mature' is the definition.
(to ripen is to mature)

I cannot understand how the rest of the clue works.

(Other definitions for ripen that I've seen before include "Come to maturity like fruit" , "Become ready to harvest" , "Become ready for eating" , "Become ready for picking" , "Get ready to eat" .)

I've seen this clue in The Telegraph.

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