Proficiency One: Flavor

Teaching Taste

My friend Kate LOVES saurkraut. My friend Ava would sooner gouge her own eyes out than even sniff the stuff. But 22 years ago, both Kate and Ava started out liking the same foods: or should I say, food. Their lives began with a single, all-encompassing taste and flavor preference: breast milk. So, how is it that Kate grows to love saurkraut, and Ava to hate it? While many of our flavor preferences are hard wired, thanks to the shared blueprint of chemosensory cells and neural structures that sense and interpret the stimuli introduced to our mouth and tongue, our tastes and preferences are actually a learned phenomenon, and class starts before we even make it out of our mother's womb.

What we perceive as “yummy,” “comforting,” or “gross” is not just about molecules binding to receptors. It is about learned associations, memory, and reward. Flavor, it turns out, is as much psychological as it is chemical.

Biological Background of Taste

Taste itself is largely hard-wired. As discussed in class, there is an objetive biological truth to the sensory information transmitted from the tongue's papillae to the brain. Each cell within a taste bud responds to one of the 5 tastes, and sends that information to the brain (Yarmolinsky, 2009). Across cultures and populations, humans are born liking sweet and salty tastes and rejecting bitter and sour ones, an adaptive system designed to guide infants toward nutrients and away from toxins (Prescott, 2015). But flavor, which combines olfactory, textural, and even temperature experiences, is different. Most importantly, unlike taste, odor preferences are not innate; they are learned through experience. 

The Neuroscience Behind the Scenes

According to the Neuropharmacology of Learned Flavor Preferences by Touzani, Bodnar, and Sclafani, there are two major ways humans and other mamals learn flavor preferences: flavor-taste learning and flavor-nutrient learning (Touzani et al., 2010). In flavor-taste learning, if a flavor (meaning an olfactory and oral experience that does not trigger any specific taste buds for sweetness, saltiness, sourness, umami, or bitterness, like artificial cherry flavoring) is repeatedly paired with a desireable taste (usually sweetness or saltiness), the animal begins to like that flavor more. The flavor essentially “borrows” the positive hedonic value of the taste it is paired with.

In flavor-nutrient learning, if a flavor is followed by calories hitting the stomach (even if the food itself doesn’t have the desired taste, like a caloric cherry flavored drink with no sweetness), animals learn to prefer that flavor because it predicts a positive “post-eating” effect. This helps explain how animals can develop strong preferences for foods that are bitter, sour, or otherwise challenging at first, such as coffee or beer. The flavor becomes valuable because it reliably predicts a positive post-ingestive outcome, like alertness from caffine, inebriation from alcohol, or plain old energy for the body from any other caloric source.

This learning is acheived through dompamine signalling via the "D1" receptors. When researchers block these dopamine receptors, lab animals often don’t learn the preference as strongly, or sometimes can’t learn it at all, regardless of the flavor-nutrient or flavor-taste conditioning used. However, once a flavor preference has been learned, it persists even if dopamine signaling is later reduced. This indicates that dopamine is critical for “writing” the memory, but not always necessary for “reading” it back. This persistence may help explain why food preferences formed early in life—or through repeated exposure—can be remarkably stable and resistant to change. 

It also turns out that the brain’s opioid system, often associated with pleasure and “liking," plays a much smaller role in learning flavor preferences than previously thought. Blocking opioid receptors with drugs like naltrexone consistently reduced how much animals consumed sweet or otherwise preferred foods, but it rarely prevented them from learning which flavors they preferred in the first place. In other words, opioids seem to modulate the intensity of enjoyment during eating, not the formation of the memory that links a flavor to a positive outcome. Dopamine appears to be responsible for writing the association while opioid signaling mainly amplifies how good that experience feels in the moment. Even when opioid signaling is suppressed, animals still “know” which flavor predicts reward; they are just less motivated to consume large amounts of it.

Filling in Flavors

A clear example of learned flavor association in humans comes from research showing that adding vanilla aroma to milk makes it taste sweeter—even when no additional sugar is added. The vanilla does not chemically increase sweetness; instead, it triggers a learned association between the smell of vanilla and the experience of sweet foods built up over a lifetime of ice cream, cake, and pastries (Penn State University, 2019). 

I tried this myself with my roommates using plain Greek yogurt. Yogurt mixed with vanilla extract—despite containing no sugars or intrinsically sweet compounds—was consistently rated as sweeter than plain yogurt. Interestingly, it was only perceived as slightly sweeter than yogurt mixed with cinnamon, though both were seen as less sweet than yogurt mixed with actual sugar. This mirrors what the literature suggests: learned flavor cues can “fill in” sweetness, but they do not fully replace it.

Over years of repeated exposure, the brain learns a simple rule: vanilla = sweetness. I guessed that cinnamon would likely have a similar effect, and in the sample pool of my roomates and I, this proved to be true. When we smell vanilla, or cinnamon, or anything else we're used to wafting out of bakeries, our brain fills in the sweetness that experience has conditioned us to expect. 

Conditioning from the Cradle

There is strong evidence that these associations begin to build before a person is even born, long before they taste solid food. In an interview with the Association for Psychological Science, Julie Mennella, a researcher at the Monell Chemical Senses Center, a Philadelphia-based research institute focused on taste and smell, talks about the early development of "flavor memories." 

Mennella’s work shows that flavors from a mother’s diet pass into both amniotic fluid and breast milk. When pregnant or lactating women consume foods containing volatile compounds—such as garlic, vanilla, carrot, mint, or even alcohol—those flavors become detectable in the fluid environments experienced by the fetus or nursing infant (Mennella & Beauchamp, 1991; Mennella et al., 1995). Infants are not passive recipients of this information; they respond behaviorally. For example, babies nurse longer and more vigorously when breast milk carries familiar or preferred flavors, such as garlic. Menella describes:

"One striking example of the plasticity and stability of the flavor memories formed comes from research on the European rabbit (Oryctolagus cuniculus). Learning occurred when flavors were experienced in either amniotic fluid or mothers’ milk [Bilko, Altbäcker, & Hudson, 1994]. After feeding pregnant and lactating does aromatic juniper berries, newborn, weanling, and even adult animals demonstrate a preference for juniper flavor without subsequent postnatal experience. We found the same thing when we looked at the infants whose mothers drank carrot juice during either pregnancy or lactation — when compared to the control group, both enjoyed the carrot-flavored cereal more at weaning. Such redundancy of dietary information may be important biologically because it provides complementary routes of transferring information on the types of foods available in the environment, should the mothers’ diet change during the course of pregnancy and lactation."

While a mammalian mother’s primary role is to nourish her young through milk, that phase is always temporary. Eventually, the infant must learn to consume solid foods and navigate its broader food environment. To make that transition possible, development has to do more than support growth: it has to teach. One of the earliest ways young mammals begin learning what to eat is through flavor cues passed down from the mother. These cues effectively act as early signals of which foods are nutritious, familiar, and worth seeking out, long before the infant ever forages—or even chews—on its own.

Regardless, some aspects of taste biology remain difficult to override. Sweet and salty preferences are universally strong in childhood, while bitterness—nature’s signal for potential toxins—is often intensely rejected (Bartoshuk, 2010). However, early exposure can modify even these responses. Mennella’s work on infant formula shows that babies exposed early to bitter, protein-hydrolysate formulas not only accept them readily, but may grow into children who are more tolerant of bitter and sour flavors overall. To an adult, these formulas taste unpleasant; to an infant, repeated exposure can make them feel normal or even comforting. Early experiences with flavor shape our culinary interests long after these "flavor memories" are set, whether we want them to or not.

So, maybe Kate's mom ate a LOT of saurkraut during her pregnancy, or maybe Kate learned that saurkraut always went with the delightful nutrition and fullness of porkchops and mashed potatoes. Maybe Kate was one of those babies fed protein-hydrolysate formula, and she was destined to love sour cabbage from the start. As chemical engineers—and eaters—it’s worth remembering that every food is more than a formulation of molecules. It’s also a prediction, a memory, and a lesson learned over time. So the next time you wrinkle your nose at something unfamiliar or find yourself craving something inexplicable it might not be your taste buds talking at all. It might just be your brain, reminding you of what it learned long ago.

Sources

Yarmolinsky, D. A., Zuker, C. S., & Ryba, N. J. P. (2009). Common sense about taste: From mammals to insects. Cell, 139(2), 234–244. https://doi.org/10.1016/j.cell.2009.10.001

Prescott, J. (2015). Flavours: the pleasure principle. Flavour, 4, Article 15. https://doi.org/10.1186/2044-7248-4-15

Penn State University. (2019). Vanilla makes milk beverages seem sweeter. https://www.psu.edu/news/research/story/vanilla-makes-milk-beverages-seem-sweeter

Touzani, K., Bodnar, R. J., & Sclafani, A. (2010). Neuropharmacology of learned flavor preferences. Pharmacology, Biochemistry and Behavior, 97(1), 55–62. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2956077/

Mennella, J. A., & Beauchamp, G. K. (1991). Maternal diet alters the sensory qualities of human milk and the nursling’s behavior. Journal of Human Lactation, 7(1), 39–45. https://doi.org/10.1177/089033449100700116

Mennella, J. A., Johnson, A., & Beauchamp, G. K. (1995). Garlic ingestion by pregnant women alters the odor of amniotic fluid. Chemical Senses, 20(2), 207–209. https://doi.org/10.1093/chemse/20.2.207

Bilko, A., Altbäcker, V., & Hudson, R. (1994). Transmission of food preferences in the rabbit: The means of information transfer. Physiology & Behavior, 56(5), 907–912. https://doi.org/10.1016/0031-9384(94)90334-4

Bartoshuk, L. M. (2010). Flavor learning in utero and infancy. APS Observer. https://www.psychologicalscience.org/observer/flavor-learning-in-utero-and-infancy

Mennella, J. A., Griffin, C. E., & Beauchamp, G. K. (2004). Flavor programming during infancy. Pediatrics, 113(4), 840–845. https://doi.org/10.1542/peds.113.4.840