Add an anosmia status condition, in which you have no sense of smell:

• Tins cannot be identified by their smell, unless they contain spinach or are empty.
• Messages involving smell, such as when you cast stone to flesh on rocks, are suppressed.
• Food detection scrolls and the spell of detect food don’t work.
• Food appraisal doesn’t work.

Not specified what things in the game might cause this condition, or if it should be a roleplay birth option.

Incantifiers should not be eligible to receive a spellbook of detect food at the beginning of the game, because it’s pretty much useless to them.

Detect food sources additionally detect potions of fruit juice, and possibly potions of booze.