這不是葡萄酒，是葡萄汁。

That isn't wine. It's grape juice.

Source: Tatoeba

Sentence Composition

=1 這不 zhèbu (coll.) As a matter of fact, ... (used to introduce evidence for what one has just asserted)
=1 這不 zhèbù connects two clauses, emphasising how the following clause substantiates the preceding clause
=2 是 shì
  1. to be (followed by substantives only)
  2. correct; right; true
  3. (respectful acknowledgement of a command) very well
  4. (adverb for emphatic assertion)
=2 是 shì variant of 是 shì
=3 葡萄酒 pútaojiǔ (grape) wine
=3 葡萄酒 pútáojiǔ wine
=4 是 shì
  1. to be (followed by substantives only)
  2. correct; right; true
  3. (respectful acknowledgement of a command) very well
  4. (adverb for emphatic assertion)
=4 是 shì variant of 是 shì
5 葡萄汁 pútáozhī grape juice