List includes foremost Tempranillo grape juice from Spain - presumably, it will show a level of acidity (6,4)
I believe the answer is:
litmus test
'list includes foremost tempranillo' is the definition.
I can't judge whether this definition defines the answer.
'grape juice from spain presumably it will show a level of acidity' is the wordplay.
I cannot really see how this works, but
'spain' could be 'es' (es is an abbreviation for Spain) and 'es' is found in the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found in the answer.
'grape juice' could be 'must' (I've seen this in other clues) and 'must' is located in the answer.
The remaining letters 'lit' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for litmus test that I've seen before include "Observer may see red after one" , "Chemical trial" .)