The Big Bang Theory: The Fermentation Bifurcation

A new episode of The Big Bang Theory, titled "The Fermentation Bifurcation,"" airs tonight!

The gang goes to a wine bar and runs into Penny's old boyfriend, Zack (Brian Thomas Smith). Also, Bernadette gets stuck spending the evening with Sheldon when she can't go wine tasting with the group, and things don't go as planned when Koothrappali introduces his new girlfriend, Claire (Alessandra Torresani).

Watch clips and a sneak preview for the episode in the videos below.

The episode was directed by Nikki Lorre and written by Steven Molaro, Jim Reynolds and Anthony Del Broccolo

"The Fermentation Bifurcation" episode of The Big Bang Theory will air tonight at 8:00 PM ET/PT on the CBS Television Network.