Taste is the sensory ability to detect the properties of molecules of solid and liquids in the mouth, generally those in food. Specialized cells on the tongue known as taste buds react with different chemicals in solids and liquids and invoke a particular sensory reception. For example an ion of an alkalai metal such as sodium triggers two different receptors. These reactions are now generally classified into five types - salty, sweet (typical of glucose), bitter (typical of quinine), sour (typical of acids) and umami (typical of monosodium glutamate). Taste works together with smell to give foods their flavor.
Taste serves as both positive reinforcement and a warning. For example, most energy rich foods taste sweet, and most toxins taste bitter.
Taste, like other things, tends to get less reliable as people age. In this case, the taste buds tend to lessen in number as people get older. This has a dual effect as most adults can tolerate healthy but bitter foods that are completely unpalatable to a child, such as broccoli.
The ability to perceive levels of taste appears to be genetic, with some people having a lesser sense of taste (and preferring spicier foods) and some having a greater sense (and, once again, avoiding broccoli)
A sudden lost of taste, the inability to distinguish different tastes, or having an atypical taste reaction, can be a symptom of a more serious underlying disorder. However, due to the importance of smell to flavor, the loss of taste sensation during nasal congestion is perfectly normal.