Why does Kaneki's perception of taste change? In the anime Tokyo Ghoul, Rize's organs are transplanted into Kaneki causing him to become a half-ghoul half-human. However, the organs transplanted are situated in his abdomen region and his tongue remains the same. 

Later, we see the ghoul researcher Ogura Hisashi say that ghouls cannot digest human food due to a particular enzyme in their body and because their tongues have a different structure, food tastes different to them. However, Kaneki's tongue had remained unaltered so he should have been able to eat and taste human food but not be able to digest them.


  


Inspite of this, we see Kaneki say that food tastes bad to him and he uses adjectives such as ash to describe the taste. My question is, even though his tongue is unchanged, why is he unable to taste human food?

This Reddit thread partially answers the question. However, most of them were guesses and I didn't find them satisfactory. The highest upvoted answer goes against the show (tongue does not change.)


I've only watched the 2 seasons of the anime, so I request you to keep the answer as spoiler-free as possible.
The ghoul DNA "infected" his whole body (look at his eyes) so it´s not too far fetched it changed the tongue as well.

Apart from physical change there is also a mental change. There is a phenomenon where patients who obtained an organ transplant notice effects on what they like or dislike, e.g. if the donor was a pianist the patient might like listening to piano more than before or even want to learn it. Kaneki's tongue could still have the same structure as before but different associations to food based on his digestive system.