Something fibrous turning up in eggs — and beer! (7)
I believe the answer is:
elastin
'something fibrous' is the definition.
I can't judge whether this defines the answer.
'turning up in eggs and beer' is the wordplay.
'turning up in' is a reversal indicator.
'eggs' becomes 'nits' (nits are insect eggs).
'and' is a charade indicator (letters next to each other).
'beer' becomes 'ale' (type of beer).
'nits'+'ale'='nitsale'
'nitsale' backwards is 'ELASTIN'.
Can you help me to learn more?
(Another definition for elastin that I've seen is " protein".)