When did Erina learn that Yukihira's father was Joichiro?

Question

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?

Answer 1

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.

Answer 2

In the series it hasn't been stated that she knows who his father is. In an earlyish arc (40's i think) his dorm mates were surprised to find out they were related, whether this knowledge spread isn't known.

Answer 3

In the most recent chapter,

Soma's relationship to Jōichirō is inadvertently revealed to her when she walks in on a conversation between her father and Sōma. At first she was in disbelief, but realized it was true after seeing the two next to each other in a recent photo. She became greatly shocked after realizing that she had been hostile towards the son of the chef she always admired.

It's been updated even on the wiki page. Go read under the Erina Nakiri section. Beware of spoilers though :P

https://en.wikipedia.org/wiki/List_of_Food_Wars:_Shokugeki_no_Soma_characters