How we taste and why we like or don't like what we taste are mysterious questions. Food preferences, it seems, are determined by multiple factors, including genes, experience and age. Here's the lowdown on "taste makers."

Q. What is "taste?"

A. Technically, "taste" refers to the sensory experiences produced by stimulation of taste receptors on the tongue and palate. "Taste sensations not only provide information about the nature of the stimuli but also produce affect (an emotion or feeling); that is, taste sensations are pleasant or unpleasant. This (mechanism) is hard-wired in the brain. Babies are born loving sweet and hating bitter," says Linda Bartoshuk, Ph.D., professor of otolaryngology at Yale University.

"This preference was handed down from our evolutionary past," explains Steven Witherly, Ph.D., president and CEO of Technical Products Inc., a food consulting firm in Valencia, Calif. "The environment was very low in salt, fat and sugar, so our sensory systems evolved to find these rare ingredients very pleasurable."

Witherly adds that there is also a psychological component — all sensations created by food in the mouth activate memory centers throughout the brain that may modify our perception.

Q. Can you adjust your taste and make it more sensitive?

A. To a certain extent. For example, if you stop eating salty or sugary foods, your taste adjusts so that when you do eat something even mildly salty or sweet, your reaction will be exaggerated. And that is a result of your perception of the food's taste, not its chemical properties. So, if you ate virtually no foods that tasted salty (such as pretzels or salty peanuts) but continued to eat foods with hidden, tasteless salt (such as bread or even tasteless salt pills), you would still become salt-sensitive, explains Marcia L. Pelchat, Ph.D., of the Monell Chemical Senses Center in Philadelphia. "It's your brain that's adjusting, not the taste."

How long does this effect take? Witherly says sodium appetite can change within weeks. "Sugar and fat are more difficult, and some scientists believe that the brain never forgets the taste of sugar or fat — especially the combination of the two."

However, the brain remembers and flips back rather quickly.

"It might take a month or more to get used to low salt, but it will take less than a week to go back," says Witherly.

Q. Is it true that as much as 80 percent of what we perceive as taste is actually smell?

A. No. It's confusing because we use the word "taste" to refer to both real taste (sweet, salty, sour and bitter) and to the sensations evoked when we put food in the mouth, says Bartoshuk. In fact, taste and smell are separate senses that combine in a unique way in the brain.

The major function of taste is to evaluate whether a food is friend or foe, whereas the major function of smell is to identify or memorize the food for future reference — was it good (e.g., nonpoisonous), and did it have calories. "So smell acts like a gatekeeper for final ingestion, and the taste of food generates the major pleasure of ingestion," says Witherly.

Q. How many odors can we sense?

A. "We have about 50 million olfactory (smell) receptors — about 500 different types finely tuned to recognize just a few odorants," says Witherly.

The olfactory system operates by analyzing chemical structure. When a molecule (or group of molecules) hits your olfactory receptors, it creates a pattern in the brain. "These patterns are somehow stored in the brain and become associated with a particular reaction, depending on whether the object you smelled does something good for you (provides calories) or bad (poisons you and makes you nauseated). Thus the smell of bacon, for example, produces a pattern that is stored in memory. When that pattern is excited, you smell bacon," explains Bartoshuk.

Q. How many tastes are there?

A. According to Witherly, the basic tastes are sweet, sour, bitter and salty, to which we add "umami" (MSG taste), "hot pepper" or vanilloid taste, "fatty acid" taste and "water" taste. We also sense texture, temperature and pain.

Q. Does taste change as we age?

A. Studies show that the sense of taste doesn't really diminish much, but the sense of smell can decline dramatically past 60, says Witherly.

Q. True or false: We have thousands of taste buds?

A. True. We have many taste buds, and each one can have as many as 50 individual taste cells. However, according to Bartoshuk, the number of taste buds varies from one individual to the next. "Nontasters" have relatively few taste buds; "supertasters" have many more. Most people are in between. "If you don't like really hot and spicy food and you find coffee too bitter, you're probably a supertaster," says Witherly.

Q. What are taste aversions, and how do they develop?

A. Taste aversions appear to result from pairing nausea with a taste. In humans, these are not actually taste aversions at all, rather aversions to odors leading to nausea. "They are more accurately called 'food aversions,'" says Bartoshuk. And according to Witherly, all it takes is one pairing of a food with gastrointestinal illness to form a permanent food aversion. This phenomenon is meant to protect us from harm, because 90 percent of all foods may be poisonous.

Q. What makes vanilla the most popular flavor?

A. Most experts believe that liking or disliking odors is a learned experience. And since vanilla is often associated with a nurturing context (e.g., Mom, breast milk, infant formula) and with pleasurable sweet and fatty foods, we have positive memories each time we smell vanilla, says Witherly.

Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.