Small wines turn out to be sources of strength (6)
I believe the answer is:
sinews
'sources of strength' is the definition.
'sinews' can be an answer for 'strength' (I've seen this before). I'm not sure about the 'sources of' bit.
'small wines turn out' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size**).
'turn out' is an anagram indicator.
'wines' anagrammed gives 'inews'.
's'+'inews'='SINEWS'
'to be' acts as a link.
Can you help me to learn more?
(Other definitions for sinews that I've seen before include "Tough tissues joining muscles to bone" , "They connect muscle to bone" , "Power" , "Strength" , "Tissues connecting muscles to bones" .)