Sour grapes? Taste, experience of sour foods depends on individual consumer

(Press-News.org) UNIVERSITY PARK, Pa. — Biting into a tart green apple is a different taste and sensory experience than sucking juice from a lemon — and both significantly vary from accidentally consuming spoiled milk. Each of these foods contains a different organic acid that gives rise to the flavor commonly referred to as “sour,” even when the taste and related mouthfeel sensations such as puckering and drying vary drastically from food to food and person to person. Now, Penn State researchers have found that while some of that difference comes from individual perceptions, the acids themselves vary in sourness, even at the same concentrations.

The researchers, who recently published their findings online in advance of the March issue of Food Quality and Preference, explained the work builds on their 2024 study that revealed roughly one in eight adults like intensely sour sensations and exceptionally sour foods. This new study dives deeper into why different acids taste differently sour, why people disagree on how sour things taste, and why some people love sour foods while others really don’t.

“Beyond just being interesting, these findings might help guide the food industry in making formulations for sour foods because these different acids have subtle taste and mouthfeel nuances to them,” said study senior author Helene Hopfer, associate professor of food science in the College of Agricultural Sciences. “We found that sourness isn’t experienced as just taste — it's also puckering and it's also drying. Equal amounts of different acids do not create equal sourness or mouthfeel. People vary widely in both how much sourness they like and how strongly they perceive it.”

The researchers recruited 71 everyday consumers — not trained tasters — who eat or drink sour foods at least once a month. The participants tasted water solutions containing equal amounts of five acids: lactic — found in sauerkraut, pickles and milk; malic — found in Granny Smith apples, fumaric — found in papayas, pears and plums; tartaric — found abundantly in grapes; and citric — in citrus fruits and juice. Each acid was tested at four increasing concentrations. Participants rated sourness, puckering, drying and overall liking.

“Because all these different organic acids are widely used by the food industry, and they're food safe, there's a lot of conventional wisdom, ‘well, you use this one for this application or use that one for that application,’” said study coauthor John Hayes, professor of food science. “But we really wanted to unpack all of that and do a systematic apples-to-apples comparison.”

The results suggest that different acids do not taste equally sour, even at the same concentration. Overall, citric acid produced the strongest sourness and puckering overall. Lactic acid produced the least sourness and puckering. More specifically, the participants generally fell into one of three groups: those who more immediately disliked the taste as sourness increased; those who more gradually disliked the taste as sourness increased; and those who liked the food experience more as the sourness increased.

The groups didn’t just taste and like sourness differently — they experienced it differently, Hayes noted. The group that more sharply disliked the taste rated sourness, puckering and drying as more intense, especially at high concentrations. This effect was strongest for non-citric acids. The opposite group that liked the sourness reported consuming more citrus fruit juices and tart fruits.

“Equal amounts of different acids do not create equal sourness or mouthfeel,” Hayes said. “People vary widely in both how much sourness they like and how strongly they perceive it. These differences matter most for acids other than citric acid and could be important for food formulation, product optimization and tailoring sour foods to different consumer segments.”

Using validated surveys, Hayes and colleagues previously found that those who like spicy food tend to have specific personality characteristics, like being motivated by rewards and an inclination toward taking risks. They also previously found that those who like and seek out bitter tastes, like pale ales, are also more prone to taking risks. However, in this study, the participants who prefer sour taste did not demonstrate different personality traits from the other groups, so sour preference seems linked to dietary exposure, not personality, Hayes said.

“We looked at whether or not personality traits were related to strong liking of sour taste because we've done a lot of work showing that people who like the burning sensation from chili peppers are risk takers and adventure seekers,” he said. “We wondered whether people who were a little more sensation seeking or risk taking and adventurous might strongly like sour taste. We thought that might explain why those one in eight adults really likes intensely sour sensations. But that didn't work out— there was no relationship.”

Study first author Astrid D'Andrea recently earned her master’s degree in food science from Penn State.

The U.S. Department of Agriculture’s National Institute of Food and Agriculture funded this research.

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