http://revach.net/article.php?id=4138

Section: Parshas HaShavua   Category: Quick Vort
Parshas Noach: Rav Berel Soloveitchik - Did Noach Get Drunk On Grape Juice?
After coming out of the Teivah and seeing the whole world destroyed because of corruption, Noach the great tzaddik who worked tireless day and night to uphold the entire world, gets drunk.  What was he thinking?

The MiShulchan Gavo'a brings from the Sfas Emes that this happened by accident.  The nature of the world changed a great deal after the devastating effects of the Mabul.  Noach planted grapes and drank an amount of wine that should not have intoxicated him, but in his first lesson about these changes, he found out that even a much smaller amount of wine will make you drunk.

Another answer he brings from Rav Berel Soloveitchik, the son of the Brisker Rov, is that the medrash tells us that the vines that Noach planted grew grapes that very same day.  Noach cut them off and squeezed them into juice.  He drank it that day.  Since it did not have time to ferment and become wine he was sure it was grape juice.  However as he he found out the hard way, just like they miraculously grew in one day, so too they also turned into wine as soon as he squeezed them.  After drinking a bit too much of this "grape juice", the great tzaddik Noach became drunk.