"Do you like white wine?"
Translation:¿Te gusta el vino blanco?
Why do you NEED the definite article here? Can someone give me the rules for when one should drop the article?
The article is used here because the subject of the sentence is being talked about as something in general. Is (all) white wine (in general) pleasing to you?
You almost always need it before a noun after gustar/encantar because those verbs generally have the subject after them, and they often talk about things in general:
I like dogs (in general) = Me gustan los perros.
She loves Italian food = Le encanta la comida italiana.
Italian food is delicious. La comida italiana es deliciosa.
Cigarettes are expensive. Los cigarrillos son caros.
How would you word the question in Spanish if you were asking about a specific white wine (e.g. the house wine)?
Your explanation is the opposite of what I was expecting. When you add the definite article ("the white wine"), it is now specific and no longer general statement (at least in English). So, I'll just have to recall that the article is typically used after gustar, and it is not intuitive for me.
does this actually have to be in usted form? if not, how would you say it in informal?