Why can't you taste food when you have a cold?
This German review supports common wisdom that the sense of taste is predominantly informed by the sense of smell. For instance, common advice to children taking "nasty" tasting medicines is to plug one's nose. Any condition that blocks olfaction, such as sinusitis from flu or other sinus infections, or blocking nasal airflow, will decrease or block olfaction and as a result, the majority of taste.


Hüttenbrink KB. [Disorders of the sense of smell and taste]. Ther Umsch. 1995 Nov;52(11):732-7. [Article in German]