One who invests in beer is upset, for example (8)

I believe the answer is:
besieger
'one who invests' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'in beer is upset for example' is the wordplay.
'in' indicates putting letters inside.
'upset' says the letters should be written backwards.
'for example' becomes 'e.g.' (short for 'exempli gratia', 'for example' in Latin).
'is' reversed gives 'si'.
'si'+'eg'='sieg'
'beer' enclosing 'sieg' is 'BESIEGER'.
Can you help me to learn more?
(Other definitions for besieger that I've seen before include "Attacker attempting to capture" , "Invader" .)
