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Food tastes different hot vs. cold for two reasons. First, warmer food releases more volatile aroma molecules, and most of what we call “flavor” is actually smell reaching the nose from the back of the mouth. Second, the TRPM5 ion channel — which transmits sweet, umami and bitter taste signals from taste cells to the brain — is steeply heat-activated, firing roughly 5–10× more strongly between 15 and 35 °C (Talavera et al., Nature 2005). Together, these effects make warm food taste richer and more intense than the same food cold.
We’ve all been there… peering into our refrigerator on a hungover Sunday morning, only to happily realize there is still a slice or two of pizza left from the late-night binge feast a few hours earlier. In that moment of desperation, any sustenance is welcome, but that cold pizza definitely doesn’t taste the same as it did the night before. The ingredients are all the same – pepperoni, cheese, jalapeños and olives – but something seems to be missing. It doesn’t seem to make any sense.
Why does the temperature make that much of a difference when it comes to the flavor of food?
Short Answer: Human beings evolved to prefer hot food to cold, as it was an evolutionary advantage that saved time for more important things, allowed us to derive more energy and nutrients, and protected us from illness. Chemically speaking, our taste perception increases with warm foods, as opposed to cold ones, based on boosted activity of the microscopic channels in our taste buds.
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From Cold Eaters To Hot Foodies
For most of our evolutionary history, the only available food was cold and raw, just like every other animal on the planet. Then, somewhere along the line, human ancestors started to cook. The earliest solid archaeological evidence of controlled fire use — burnt sediment and bone at Wonderwerk Cave in South Africa — dates to about 1 million years ago, with habitual fire use only becoming widespread around 400,000 years ago. (Richard Wrangham’s influential “cooking hypothesis” pushes regular cooking back to Homo erectus around 1.9 million years ago, but that earlier date is still contested.) Either way, once early hominids could build fires to cook their food, ward off predators and stretch their waking hours into the night, our evolutionary trajectory changed.
This was one of the first major efforts by humankind to outsource certain biological responsibilities – namely chewing and digesting raw food – which freed up a huge amount of time. Cooking softens cell walls, denatures proteins and gelatinizes starches, so the gut has far less work to do. In effect, heat does part of the digestive job before food ever reaches the stomach.
The production of heat, and its application to food, causes chemical reactions and changes to the food, changing the basic nature of meats, grains and vegetables to make them much easier to digest. Think of a cow, with its multiple stomachs, where regurgitated food must pass back into the mouth to be further chewed in order to be fully digested. Heating up our food allowed us to spend our energy, both mental and physical, in the pursuit of greater things. (One thing humans do still have, somewhat surprisingly, is unusually strong stomach acid: a 2015 PLOS ONE survey by Beasley and colleagues put human gastric pH at around 1.5 — closer to obligate scavengers than to typical omnivores — most likely a defence against pathogens in scavenged or undercooked meat.)
By heating food, we increase the caloric availability of our food, from which we derive our energy. Carmody and Wrangham’s 2009 review found that cooking can boost the small-intestinal digestibility of starch by anywhere from ~28% (oats) to over 100% (green bananas), and that raw starch is only about 50% digestible compared with 95%+ for cooked — a substantial energy windfall over an evolutionary timescale.
Aside from being easier to digest, cooking food can eliminate far more food-borne illnesses, and is more pleasant to our senses. When you heat up food, the molecules become more volatile, flying off the food in the form of aromas, which keep us coming back for more. Our senses of smell, therefore, has evolved to encourage us to eat foods that are healthier for us, particularly those that smell and taste better when they are cooked, such as meats, vegetables, beans, etc.
However, that doesn’t full explain the sense of taste, specifically why cooked foods tend to taste better than cold foods.
Our Talented Tongues
A great deal of research has gone into taste and smell, because food manufacturers want to understand everything they can about what flavors and tastes appeal to consumers. They also want to determine ways to mask unpleasant flavors, and that all comes down to the taste receptors in our tongue.
As it turns out, the tiny ion channels in our taste cells — most importantly TRPM5, which carries sweet, umami and bitter signals from receptor to nerve — tend to fire much harder when warm. Talavera and colleagues showed in Nature in 2005 that TRPM5 activity rises sharply between roughly 15 and 35 °C, and that warming a sweet stimulus from cold to body-temperature can increase the perceived sweetness several-fold. Foods and fluids therefore have more powerful sweet, umami and bitter flavors in our mouth when they are warm — which can work both ways, for flavors that are good and for ones that are unpleasant.
For example, people prefer their coffee hot mostly because the heat releases volatile aroma molecules — caramel, chocolate, fruity, and woody notes — that flatten out as the cup cools. (Lukewarm coffee actually tastes more bitter and less complex, not less.) On the other hand, when considering something like ice cream, the sweet taste is only fully activated when the ice cream begins to warm and melt in our mouth, not when we simply lick the top of an ice-cold carton of mint chocolate chip. Those tiny receptor channels in our tongue, which pass along messages about flavor, do not function as well when the substance is cold.
The adult human tongue carries roughly 2,000 to 8,000 taste buds (a commonly cited estimate is around 4,000–5,000), each containing 50 to 100 cells. The cells are not interchangeable: separate populations of receptor cells are tuned to sweet/umami/bitter, sour, and salty, and they pass their signals on through TRPM5 and other channels. Some foods are preferred cold, such as soda, while others are preferred hot, such as tea and cocoa. Hot food doesn’t necessarily mean that it is better — it just means that a certain flavor profile will be more intense. Cranberry juice, which already has quite a bit of an astringent flavor, wouldn’t be nearly as pleasant when warmed up and that flavor profile is amplified.
Understanding more about this delicate balance, and the process of taste perception, helps food scientists develop new methods to mimic flavors and potentially improve the health of our dietary intake.
Over the course of evolutionary history, our taste buds have mainly developed to prefer warmer foods, in the search for more powerful and rewarding flavors. So, while that slice of cold pizza may be just what the doctor ordered on that hungover Sunday morning, the salty and savory flavors on that slice would be even more satisfying if you popped it in the oven first and gave your taste buds a real treat!
