The Perfect Temperature for Soup, According to Science

Fudio/iStock via Getty Images
Fudio/iStock via Getty Images

Finding the right temperature for soup can be difficult. On one hand, few culinary experiences are as unsatisfying as sipping on a lukewarm broth. On the other hand, nobody enjoys burning their taste buds on nuclear-heated stock. Luckily, you can embrace your inner Goldilocks and find a soup temperature that’s “just right”—with science!

Studies confirm what chefs have long suspected: Temperature affects the taste of food. Cheddar cheese generally tastes more sour when warmed, while a savory ham will seem saltier as it cools. The reasons for these flavor differences are complex; sometimes they’re caused by receptors on the tongue and other times by chemical changes in the food itself. Research shows that some foods are epigenetically altered when heated or cooled. Tomatoes, for instance: The genes that help express a tomato’s full flavor profile are “turned off” when exposed to cool temperatures. That’s why some cookbooks warn not to refrigerate them.

The same principles also apply to soup. Different temperatures can accentuate, or dull, different aspects of a stock’s flavor profile.

In 2017, researchers in Spain published a study in the International Journal of Food Properties that tested the incidence of taste compounds—such as amino acids and nucleotides—in a traditionally cooked chicken broth. Samples were cooked for three to five hours, with temperatures ranging from 86°C to 103°C (that’s 185°F to 217.4°F). The team discovered that taste compounds, including those associated with umami, increased with temperature. Flavor compounds were also boosted by longer cooking times, but the effect was temperature-dependent.

In other words, the hotter the soup, the more flavorful it can be. It’s important, however, to make a distinction between cooking temperature and serving temperature. Nobody should serve soup at 217°F. Skin exposure to a liquid over 150°F can cause burns almost instantly [PDF]. There’s no point in boosting the umami of your soup if you can’t feel your tongue.

Woman in a cafe eating hot soup
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As soup cools, its flavor profile will change. According to a 2016 study in the journal Chemical Senses, umami flavors will deteriorate as a soup drops to (and below) room temperature. It will also taste saltier. This phenomenon is described in a handful of other studies, including a 2015 work published in the journal Appetite. In that study, researchers asked eight trained panelists and 62 untrained panelists to rate the saltiness of salt water, chicken broth, and miso soup. Temperatures ranged from 40°C to 80°C (104°F to 176°F). The trained panelists perceived no difference in the saltiness of the hot and lukewarm soups, but the Average Joes said the colder soups tasted saltier (the study didn’t go into the reasons why, however).

Temperature also affects other flavors. A 2012 study in Chemosensory Perception showed that sourness was most intense when a solution was warm and bitterness most intense when it was cold. Other studies show that our perception of sweetness is enhanced with cold foods, which may explain why frozen treats such as ice cream can taste sickly-sweet when melted [PDF].

But back to our original question: How do I find the ideal temperature for serving soup?

The annoying answer is: It depends! It depends whether you prefer a bowl that’s a pinch salty, a smidge umami, or something else. It also depends if you’re among the 20 percent of people who are “thermal tasters” most sensitive to food temperature. Among this group, “heating or cooling small areas of the tongue draws out a taste sensation without the presence of food or drink,” according to a press release about the Chemosensory Perception study.

Generally, the best serving temperature probably hovers around the pain threshold for the tongue, which is approximately 153°F [PDF].

There are a few reasons why. Most people will want to serve their soup at the warmest temperature possible without causing pain. Our taste buds contain small, heat-sensitive proteins called TRPM5 channels, which are important for the perception of umami and perform best when food is warm. High temperature foods also emit more aromas, an important factor that amplifies the intensity of taste. “As heat is applied to food, its essential oils, or volatiles, are released, which increases the food’s aroma and flavor,” food writer Amanda Hesser explains in The New York Times. As a hot dish cools, the flavors change and develop. She also suggests contrast, like topping hot chili with cool sour cream, to animate taste receptors.

Scientists have done a lot of research about where to draw the line between a liquid that’s “just right” and “too hot”—and a temperature ranging between 136°F to 162°F appears to be the best bet, according to a recent analysis in The Journal of Food Science. For soup-lovers, anything significantly warmer than 170 degrees will probably require tiny sips and spoon-blowing. Anything cooler than 130 might feel merely warm. Something in between should satisfy your taste buds without destroying them.

Not-So-Fancy Feast: Your Cat Probably Would Eat Your Rotting Corpse

Tycson1/iStock via Getty Images
Tycson1/iStock via Getty Images

Cat enthusiasts often cite the warmth and companionship offered by their pet as reasons why they’re so enamored with them. Despite these and other positive attributes, cat lovers are often confronted with the spurious claim that, while their beloved furry pal might adore them when they’re alive, it won’t hesitate to devour their corpse if they should drop dead.

Though that’s often dismissed as negative cat propaganda spread by dog people, it turns out that it’s probably true. Fluffy might indeed feast on your flesh if you happened to expire.

A horrifying new case study published in the Journal of Forensic Sciences offers the fresh evidence. The paper, first reported by The Washington Post, documents how two cats reacted in the presence of a corpse at Colorado Mesa University’s Forensic Investigation Research Station, or body farm, where the deceased are used to further forensic science for criminal investigations.

The study’s authors did not orchestrate a meeting between cat and corpse. The finding happened by accident: Student and lead author Sara Garcia was scanning surveillance footage of the grounds when she noticed a pair of cats trespassing. The cats, she found, were interested in the flesh of two corpses; they gnawed on human tissue while it was still in the early stages of decomposition, stopping only when the bodies began leaching fluids.

The cats, which were putting away one corpse each, didn’t appear to have a taste for variety, as they both returned to the same corpse virtually every night. The two seemed to prefer the shoulder and arm over other body parts.

This visual evidence joins a litany of reports over the years from medical examiners, who have observed the damage left by both cats and dogs who were trapped in homes with deceased owners and proceeded to eat them. It’s believed pets do this when no other food source is available, though in some cases, eating their human has occurred even with a full food bowl. It’s something to consider the next time your cat gives you an affectionate lick on the arm. Maybe it loves you. Or maybe it has something else in mind.

[h/t The Washington Post]

Wolf Puppies Play Fetch, Too, Study Finds

Christina Hansen Wheat
Christina Hansen Wheat

It took thousands of years of selective breeding for wolves to become the Golden Retrievers you see at dog parks today. Domesticated dogs are very different from their wild counterparts, but according to a new study, they may have a surprising trait in common. Researchers found that some wolf puppies are willing to play fetch with total strangers, suggesting that following human commands is intrinsic to canines.

For their study in the journal iScience, researchers from Stockholm University in Sweden set out to find how domestication affects behaviors in young wolves. They raised litters of wolf and dog pups separately from 10 days old and placed them in various scenarios.

When the scientists tested how the wolf puppies would respond to a game of fetch, they expected to be ignored. Chasing a ball and bringing it back requires understanding human commands and obeying them—abilities that were thought to only have emerged in dogs post-domestication.

The first two wolf groups met expectations by showing little interest in the toy, but something different happened with the third set. Three eight-week old pups went after the ball and brought it back when they were encouraged to do so. This was the case even when the person giving the commands was someone they had never met before.

Even though most of the puppies didn't play fetch, the fact that those who did belonged to the same litter indicates a "standing variation" for a retrieving trait in wolves. "When you talk about a specific trait in the context of standing variation, it means that there is variation for the expression of this trait within a given population," co-author Christina Hansen Wheat tells Mental Floss. "For our study it suggests that, while probably rare, standing variation in the expression of human-directed behavior in ancestral populations could have been an important target for early selective pressures exerted during dog domestication." In other words, ancient people seeking to domesticate wolves might have focused on some wolves' innate ability to follow human commands.

The first dogs were domesticated as far back as 33,000 years ago. Over millennia, humans have selected for traits like loyalty, friendliness, and playfulness to create the modern dog, but these new findings could mean that the dog's earliest canine ancestors were genetically predisposed toward some of these behaviors.

"All three litters were brought up under identical and standardized conditions across years," Hansen says of the pups in the study. "With this significant effort to control the environmental conditions, it is likely that the differences in behavior across litters to some extent have a genetic basis."

After raising the dog and wolf litters for three years and completing that part of their study, the researchers will continue to analyze their data to see if there are any other adorable (or weird) traits the two groups share.