Spirits raised after swallowing a litre (6)
I believe the answer is:
morale
'spirits' is the definition.
(I've seen this before)
'raised after swallowing a litre' is the wordplay.
'raised' becomes 'more' (I can't justify this - if you can you should give a lot more credence to this answer).
'after swallowing' is an insertion indicator.
'litre' becomes 'L' (abbreviation).
'a'+'l'='al'
'more' enclosing 'al' is 'MORALE'.
Can you help me to learn more?
(Other definitions for morale that I've seen before include "external confidence" , "Degree of optimism (of troops, perhaps)" , "State of mental confidence" , "Spirits" , "Esprit, degree of confidence" .)