Guys, before you get down on the poster, I do believe that Chrisy is referring to themselves as the one having a "thick head" meaning a little dense, that's why, the next part of the phrase is a direct question about when to add the yeast.
I think we would say something akin to "I'm a little dense with this wine stuff, when do you add the yeast?" or "I'm a little confused by all this, when do you add the yeast."
Or maybe, "You have something with a thick head [here] Peter, when do you add..." or perhaps, "Peter, you're dealing with a person with a thick head here, please clarify as to when to add the yeast."
Methinks you're a little quick on the trigger here gang, I read the poster as being self-abasing, not attacking the answerer. The "you" who has a thick head they're referring to is themselves.
Maybe it's because I've been watching a lot of Masterchef Australia/New Zealand that I'm seeing the linguistic differences.