Minor mistake to knock back this beer? (4)
I believe the answer is:
pils
'beer?' is the definition.
'minor mistake to knock back this' is the wordplay.
'minor mistake' becomes 'lip' (I can't explain this - if you can you should believe this answer much more).
'to knock' is a reversal indicator (I've seen 'knocking' mean this).
'back' suggests the final letters (I've seen 'back of' mean this).
The final letter of 'this' is 's'.
'lip' in reverse letter order is 'pil'.
'pil'+'s'='PILS'
Can you help me to learn more?
(Other definitions for pils that I've seen before include "Type of lager" , "Lager beer" .)