The Big Bang Theory season 9
Penny runs into her ex-boyfriend Zack at the wine-tasting event in The Big Bang Theory season 9 episode 13CBS

The Big Bang Theory season 9 returns with a new episode on 28 April where Leonard, Penny, Howard, Rajesh and his girlfriend Claire will head to a wine bar. Episode 22 is titled, The Fermentation Bifurcation, which will air on 28 April at 8pm EST on the CBS Network.

The official synopsis of the episode reads as follows:

Click here to watch the episode via live stream online on CBS All Access. You can also click here to watch it online (only in the US).

A pregnant Bernadette is forced to spend her evening with Sheldon, while the gang goes out drinking. At the bar, Penny runs into her ex-boyfriend Jack, and he will hit on Raj's girlfriend, Claire. As per the latest promo for the episode, Penny tells everyone, "If you guys are free this weekend, I won a night of wine tasting from work."

Leonard says, "That sounds fun," and complains, "How come we scientist don't win free stuff like sales people do?" To which Howard replies, "Because we are not in it for the stuff, we are in it for the groupies."

Sheldon then joins the discussion and says, "Personally, I find the notion of external reward demeaning. I pursue science for the intrinsic joy of discovery." But Amy criticises him and says, "But you always say that you want to win a Nobel prize." And an annoyed Sheldon replies, "I also say that don't contradict me in front of my friend, but that you don't remember."

Rajesh agrees to go, while Sheldon declines Penny's offer and adds, "Wine again? No thank you. I like my grapes the old-fashioned way, in a juice box."

But Amy decides that she will go. Howard also joins the gang, leaving Bernadette behind.

Further, Sheldon says, "Well Bernadette looks like Saturday night, it's you and me!"

While the rest of the gang go wine tasting, Bernadette will spend her evening with Dr Cooper.

Do know what happens ahead, do not miss this Thursday's episode of The Big Bang Theory, which airs at 8pm EST on the CBS Network.