'de vin' vs 'du vin'

Question

Hello Kwiziq team and learners. 
l am just wandering why in the two following sentences the 'de' proposition is used differently? 
Sentence 1 - Vous êtes un amateur de vin?
Sentence 2- Vous êtes un amoureux du vin?
 
I look forward to reading the reply :)

Accepted Answer

Bonjour Paris,
That's an excellent question!
These expressions are "expression figées", aka set phrases:
un.e amoureux/euse de +[name] or du/de la/de l' + [word] or un.e amateur/trice de +[word] (the latter is far more idiomatic)

un amoureux de Shakespeare = a Shakespeare lover
une amoureuse de la nature = a nature lover
un amateur de brocantes = a lover of flea markets

I hope this is helpful.
Bonne journée !