Starch source idiot put into sparkling wine (7)
I believe the answer is:
cassava
'starch source' is the definition.
'cassava' can be an answer for 'source' (I have seen 'Source of tapioca ' mean 'cassava' so perhaps 'source' could also mean 'cassava'). I'm unsure of the 'starch' bit.
'idiot put into sparkling wine' is the wordplay.
'idiot' becomes 'ass' (I've seen this before).
'put into' is an insertion indicator.
'sparkling wine' becomes 'cava' (I've seen this before).
'ass' inserted inside 'cava' is 'CASSAVA'.
Can you help me to learn more?
(Other definitions for cassava that I've seen before include "Tropical American starchy plant" , "Root crop of the tropics" , "Starchy crop" , "starchy food" , "Edible tropical root" .)