A loyal reader sent in a question that well illustrates a common sensory effect we encounter just about every day in one way or another. She noted that coffee makes chocolate taste better, and wondered why?
basic tastes (sic) in chocolate and coffee. Chocolate primarily has bitter and sweet tastes (taste being what you perceive on the tongue). Black coffee has a strong bitter taste, and hardly any sweet. As an aside, the other compounds in both chocolate and coffee that give them the great flavors we all know and love are mostly "volatile" compounds that are perceived by the olfactory bulb in the upper reaches of the cavernous nasal cavity, which are unimportant for the illustration of this effect.
Adaptation occurs when we repeatedly perceive something over a short period of time. When this happens, our ability to perceive that particular thing becomes lessened. For example, how many of you notice right now that your saliva is salty? None of you, right. However, if we were to completely dry the saliva off of your tongue for a few minutes and then let it replenish, you could perceive the saltiness for a few seconds or minutes before you become "adapted." Another illustration - how many of you feel the texture of your clothes against your skin? Or hear the hum of the air conditioner? Adaptation is the body's way of filtering out sensory information so that we can pay attention to new events, which tend to be the most interesting or important.
This type of effect happens all of the time during meals, and chefs have to pay particular attention to it from one course to the next lest some adaptation effect causes a perfectly balanced dessert to taste extremely bitter because it was preceded by a too-sweet sorbet. Regular wines aren't paired with desserts because the overwhelming sweetness in most desserts would adapt your palate to sweet flavor, thus making the wine become bitter. Sweet dessert wines don't get overpowered as much. And the biggest challenge to chewing gum lasting forever is your palate becoming adapted to the constant flavor stimulus, not gum itself being unable to release flavor for a long period of time.
The dessert above is the "Chocolate and Coffee Sampler" from the Fall 2005 menu in the American Bounty Restaurant.
If you have any questions about sensory effects during meals or otherwise please feel free to email me and I'll do my best to address it in an upcoming entry!