Why may foods not taste as good when you have a cold?

Answer 1

When you put food in your mouth, odor molecules from that food travel through the passage between your nose and mouth to olfactory receptor cells at the top of your nasal cavity, just beneath the brain and behind the bridge of the nose. If mucus in your nasal passages becomes too thick, air and odor molecules can't reach your olfactory receptor cells. Thus, your brain receives no signal identifying the odor, and everything you eat tastes much the same. You can feel the texture and temperature of the food, but no messengers can tell your brain, "This cool, milky substance is chocolate ice cream." The odor molecules remain trapped in your mouth. The pathway has been blocked off to those powerful perceivers of smell--the olfactory bulbs.

Answer 2

A cold affects the respiratory system, especially the nose and sinuses. Smell affects taste. When we cannot smell, our taste buds are left to tell us how food tastes---but without the element of smell / odor. Taste buds are limited and by themselves do not (cannot) give us the full picture.