My mom grew up on a dairy farm and said you could always tell when the cows got into the wild onions. Diversity is good, but flavors do come through in the milk, so there are some things that you want to avoid.
Full disclosure: I never finished the book (my attention wandered elsewhere), but I did get as far as this scene.
ETA: Around this part of the book the words "hagrid" and "dumbledore" appear, suggesting J.K. Rowling was reading this around when she named the characters in Harry Potter.