I believe there is a typo in the sentences. It should read 'sweeter' and not 'sweater'.

Anyway, coming to our discussion:
'French wines taste sweeter than Italian wines do' is correct. (Comparing verb with verb)

Alternatively, you could rephrase this sentence as 'French wines are sweeter than Italian wines.' (Comparing adjective with adjective)

Hope this helps :-)

confuse mind wrote:Which of the following is correct:

French wines taste sweeter than Italian wines

or

French wines taste sweeter than Italian wines do


Please explain the reasoning

Both are correct.

First one is correct the because the verb (taste) is implied and you can omit it in the second half. You can also put do/does as you did in the second.

Second one is gramatically correct as it is written, but it is a general convention to put do just after than.

French wines taste sweeter than do Italian wines.