Unbound cache / Timed out DNS cache entries cleaned out?

[Paketix]

Hello,
Question regarding Unbound cache handling ...
Are timed out cache entires (e.g. www.test.org <http://www.test.org/> 300s timeout elapsed) deleted/cleaned from cache at a regular interval?
If not ... how does the memory containing timed out cache entries getting re-used?
Tried to find the code in source to get a clue about this but was not successful in locating it.
Thanks for any 'enlightenment' :)
/pat
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