When did Erina learn that Yukihira's father was Joichiro? It is a known fact that Yukihira Soma is the son of one of the world's most famous chefs, Yukihira Joichiro.

When did Nakiri learn that Yukihira Soma's father was Joichiro? In which chapter?
From last page of chapter 150, "Board Game", Erina overheard Souma revealed that Jouichiro is his father.



After that, on chapter 151, "The Outbreak of War", Erina saw a picture of Souma and his father.