Round alternative to 1 gets mature in small barrel (5)
I believe the answer is:
bagel
'round alternative to 1' is the definition.
I can't judge whether this definition defines the answer.
'mature in small barrel' is the wordplay.
'mature' becomes 'age' (synonyms).
'in' is an insertion indicator.
'small barrel' becomes 'bl' (abbreviation; 'small' asks for a short form).
'age' placed into 'bl' is 'BAGEL'.
'gets' acts as a link.
Can you help me to learn more?
(Other definitions for bagel that I've seen before include "Ring-shaped bread product" , "Doughnut-shaped bread roll" , "round fare" , "Ring-shaped bread roll" , "Hard doughnut-shaped roll" .)