Why Do Sour Foods Cause You To React Oddly?

Sour candies exist in our social mind at the bizarre crossroads of confectionery and masochism. Very few other foodstuffs (aside from hot sauces) have ad campaigns that actively antagonize consumers by challenging them to push their taste buds to the extreme. When it comes to candy marketing, chocolates are likened to luxury, candy bars have their mainstream appeal, and classic confections like hard candies, taffy, and gummies play on nostalgia and an old-timey aesthetic. But sour candy, from its neon-electric color design to its face-puckering intensity, has always been directed toward the thrill-seeking kids and kids-at-heart.

Why do sour candies appeal to kids so much? Maybe it's because when we're young, we crave new and extreme sensory stimulation, and sour candies are the flavor equivalent of licking a 9-volt battery. Sour candies are so stimulating, they can even trigger involuntary muscle contractions and other physical reactions.

Some would say that intense stimulation and involuntary reaction are the reason for sour candies' appeal in the first place, hence even adults who grew up on the confectionary still enjoy the zing of flavor from the occasional lemon head. We remember the proverbial sour candy arms race when manufacturers pumped out products that promised the most extreme eye-tearing, face-squishing, tongue-quenching reactions. The eternal pursuit of the most intense sour candy has us asking: why do sour foods cause us to react oddly in the first place?

To get the full scope of humans' sour response reflex, we first should understand what makes sour candy sour, and how we perceive taste. According to Live Science, our perception of sour has a direct relationship to acidity.

Our taste buds are made up of a variety of cells that are uniquely sensitive to molecular variation. A subset of those taste receptor cells helps us measure a substance's concentration of free hydrogen ions, also known as pH (according to Clemson). This trait allowed our ancestors to better identify fruits and vegetables that contain essential vitamins and minerals. 

Ironically, Live Science suggests humans used to be able to produce our own ascorbic acid (vitamin C), but because our early diets featured so much acid-abundant fruit, the genetic trait disappeared among the species.

Foods that contain organic compounds like citric acid, malic acid, tartaric acid, and fumaric acid typically trigger our sour taste receptors, and sour candies use concentrated amounts of these compounds to overwhelm the senses. In fact, the ubiquitous white powder coating that adorns all the great sour candies is simply crystallized citric acid (via Mashed).

Though citric acid isn't inherently bad for you, consuming high concentrations can erode tooth enamel and can acid-burn sensitive areas of your mouth (according to Popular Science). Thankfully, taste bud cells regenerate completely within two weeks, so only the damage to tooth enamel is a lasting — and serious — concern.

In addition to chemical reactions resulting in an acid burn, sour candies also elicit a physical, reflexive reaction called the rejection response. Triggered by overly sour, bitter, or spicy foods, the rejection response consists of a series of withdrawal reflexes; many experts believe it evolved as a way of avoiding foods that may be toxic or poisonous to humans (according to Science Direct).

It's theorized that reflexive face scrunching (or pucker) of the sour or bitter rejection response is an innate defense mechanism to prevent ingesting overly acidic or even rancid foods (via Mashed). Puckering also provides a visual cue to our social group of whether or not the food is safe to eat.

The unique (and somewhat frustrating) thing about human dietary evolution is our disposition to crave the hyperstimulation of flavors that we are evolutionarily supposed to avoid. Humans evolve sour, bitter, and spicy rejection responses to avoid toxic or damaging foodstuffs, then we proceed to not only breed the foods to be more intense than their predecessors, but we even concentrate the acidic elements to torture our taste buds with extreme flavors.

Overly sour foods cause us to react oddly because our sense of taste evolved to detect subtle chemical differences to preserve our health, but when counterbalanced with sweet, sour foods manage to confuse our rejection response. That's why sour candies are just plain fun — they challenge you to push the perception of taste, which expands the palate and makes flavor an immersive experience.