White whine - indefinite article or not?

Hi, I have a question about articles with uncountable nouns. Here is my example:

I pick up a bottle of wine at a liquor retail place and ask the cashier:

"Is this white wine?"

"Is this a white wine?"

Which is correct? OK, I think it should be "is this white wine", because uncountable. But I see that sommeliers say, "OK, this is a red wine from Veneto".

Could both be correct?

Thanks.