The Ideal Temperature for Soup, Backed by Science

Determining the optimal temperature for soup can be tricky. On one hand, few culinary experiences are as disappointing as sipping lukewarm broth. On the other hand, no one enjoys scorching their taste buds on a soup that’s too hot. Fortunately, you can channel your inner Goldilocks and find that perfect soup temperature that’s ‘just right’—with the help of science!

Research confirms what chefs have suspected for years: Temperature plays a crucial role in the taste of food. Cheddar cheese tends to taste more sour when warmed, while savory ham becomes saltier as it cools. These flavor changes are due to a mix of tongue receptors and chemical transformations in the food itself. Studies reveal that some foods are altered on a genetic level when exposed to heat or cold. Take tomatoes, for instance: The genes responsible for expressing their full flavor are ‘switched off’ in cooler temperatures. This is why some cookbooks advise against refrigerating them.

The same principles apply to soup. Variations in temperature can bring out or suppress different flavor notes in the stock.

In 2017, Spanish researchers published a study in the *International Journal of Food Properties*, where they analyzed the presence of taste compounds—such as amino acids and nucleotides—in traditionally prepared chicken broth. The broth samples were cooked for three to five hours, with temperatures varying between 86°C and 103°C (185°F to 217.4°F). The research team found that higher temperatures resulted in an increase in taste compounds, including those associated with umami. The flavor compounds also intensified with longer cooking times, although the effect was temperature-dependent.

In essence, the hotter the soup, the more flavorful it becomes. However, it's crucial to distinguish between cooking temperature and serving temperature. Serving soup at 217°F is not ideal. Skin exposure to liquids above 150°F can cause burns almost instantly [*PDF*]. Boosting the umami of your soup is pointless if you can't taste it due to burns on your tongue.

As soup cools, its flavor profile shifts. A 2016 study published in *Chemical Senses* showed that as soup drops to room temperature (or lower), its umami flavors degrade. Additionally, it tastes saltier. This finding is also noted in a 2015 study published in *Appetite*. In that study, eight trained panelists and 62 untrained participants were asked to rate the saltiness of salt water, chicken broth, and miso soup at temperatures between 40°C and 80°C (104°F to 176°F). While the trained panelists noticed no difference in saltiness between hot and lukewarm soups, the untrained participants perceived the cooler soups as saltier (though the study did not explore the reasons behind this).

Temperature also influences other flavors. A 2012 study in *Chemosensory Perception* found that sourness was most intense when a solution was warm, while bitterness was heightened at cooler temperatures. Additional studies suggest that sweetness perception is more pronounced in cold foods, which may explain why frozen treats like ice cream taste excessively sweet as they melt [*PDF*].

Returning to our initial question: How do you determine the perfect temperature for serving soup?

The frustrating answer is: It depends! It depends on whether you prefer your bowl a little salty, a touch of umami, or something else entirely. It also depends if you're part of the 20 percent of people who are “thermal tasters,” meaning you are especially sensitive to food temperature. According to a press release about the *Chemosensory Perception* study, in this group, “heating or cooling small areas of the tongue elicits a taste sensation without the presence of food or drink.”

In general, the best serving temperature likely sits around the pain threshold of the tongue, which is approximately 153°F [*PDF*].

There are a few reasons behind this. Most people prefer to serve their soup at the highest temperature possible without causing discomfort. Our taste buds contain heat-sensitive proteins known as *TRPM5 channels*, which play a key role in perceiving umami and work most effectively when the food is warm. Hot foods also release more aromas, which amplify the overall taste experience. As Amanda Hesser explains in *The New York Times*, “As heat is applied to food, its essential oils, or volatiles, are released, which increases the food’s aroma and flavor.” As hot dishes cool, their flavors evolve. Hesser also suggests contrast, such as topping spicy chili with cold sour cream, to engage the taste receptors.

Scientists have conducted extensive research on where to draw the line between a liquid that’s “just right” and “too hot.” According to a recent analysis in *The Journal of Food Science*, temperatures between 136°F to 162°F seem to be ideal. For soup enthusiasts, anything over 170°F will likely require careful sipping and spoon-blowing, while anything cooler than 130°F may feel just lukewarm. A temperature in between should hit the sweet spot, satisfying your taste buds without overwhelming them.