'The Big Bang Theory' Season 9 episode 22 spoilers: Penny's ex Zack is back

Next week's episode of "The Big Bang Theory" will see the gang running into Penny's ex Zack at a wine tasting party. The episode is titled "The Fermentation Bifurcation," and according to spoilers, Zack will try to hit on Raj's girlfriend.

Raj has been dating two women for a while now, and it's going great for him. But Claire might not be on board with the current scenario, and she might soon force Raj to make a final decision.

Elsewhere in the episode, fans will see Sheldon spending time with a pregnant Bernadette as both of them decide to stay home instead of going to the wine tasting. Surprisingly, Sheldon is a sweet and caring host and Bernadette will have a good evening with Sheldon.

The official synopsis for "The Fermentation Bifurcation" reads: When Leonard, Penny, Amy, Howard, Raj and Claire all go out to a wine tasting party and they run into Zack who hits on Claire. Meanwhile, Bernadette and Sheldon spend the night at 4A where they play games and end up having a fun night.

Meanwhile, the April 21 episode will see Sheldon and Leonard getting into a fight after the latter expresses his reluctance to attend a roommate agreement meeting. Penny and Amy will be forced to choose sides, and Leonard will get offended when his wife supports Sheldon.

The episode will also see best friends Raj and Howard getting into a fight after Howard gets bugged with Raj bragging about dating two women. Although Raj begins by complaining about the difficulties of dating multiple women, Howard soon realises that his friend is actually proud that he's dating Emily and Claire and that he sees it as an accomplishment.

"Everyone must choose sides when a small argument between Leonard and Sheldon erupts into a heated fight during a group get-together," the summary for "The Viewing Party Combustion" reads.

"The Big Bang Theory" airs Thursdays on CBS. The episode can be watched live through CBS All Access.