When you consider the earthy aroma of a cup of cappuccino or the salty tang of a potato chip, you may overlook the sounds they make as you savor them. The glug-glug of coffee as it’s poured into your mug, the crackle of the chip on your teeth, even any music playing in the background—these details may not capture your attention. Nevertheless, sound actually plays a big role in the flavor of food: It can color our perception of smell and taste and even alter the biochemical properties of what we eat.
Our sense of taste starts with the taste buds embedded in the fleshy bumps on our tongue, nose, and throat. Smell has its origin in receptors lining our nostrils and in retronasal passages inside the mouth and back of the throat. While taste receptors are coded to recognize only five basic tastes (sweet, sour, salty, bitter and umami) plus the presence of fat, smell allows humans to recognize up to one trillion scents. Over 150 years ago, French perfumerist G.W. Piesse speculated that there might be a link between our senses of hearing and smell. He even designed a strategy for cataloguing smells according to analogous auditory pitches. But it wasn’t until the early aughts that anyone was able to show that sound can directly influence our experience of food.
In 2003, Charles Spence, a professor of experimental psychology at Oxford University, where he studies the interplay of the five human senses, invited 20 research subjects to his lab to try to answer a question that had been nagging at him: Could the sonic quality of a chip’s crunch alter one’s perception of the chip’s taste? He had each subject enter a soundproof booth, sit in front of a microphone and don headphones, a setup that allowed him to tweak both the frequency and volume of the sound the subject heard when she ate a Pringles potato chip. What he found was that participants rated the chips that made a higher-pitched and louder crunch 15 percent fresher than the softer chips, though the chips were identical.
Sound can also change the taste of food more directly, by altering the food itself.
In the decade or so since, Spence and others have amassed evidence that what we hear when we consume food—whether it’s the sound the food makes, the music in a restaurant, or even pure tones or blasts of white noise—can make our food seem sweeter, more bitter, more savory or more fresh, depending on the quality of that sound. Loud background noise in restaurants, for example, can diminish our sense of the sweetness or saltiness of food. Sound can also influence people’s consumption rates, their food choice preferences, and even how much they consume.
A number of explanations have been put forward: everything from multisensory integration and associative learning to expectations. How the process works in the brain was clarified in 2010, when researchers at the Nathan S. Kline Institute for Psychiatric Research in Orangeburg, New York, proposed a possible mechanism. They discovered that something called the olfactory tubercule, a structure at the base of the brain that plays a role in the detection of odors, responds, oddly enough, to sound. What’s more, sound can work on flavor not just through perception but possibly also at the level of biochemistry.
Sound can also change the taste of food more directly, by altering the food itself. Ultrasound, or ultrasonic waves, has the same physical properties as other sound waves, but with a frequency above the range of human hearing. Before World War II, the food industry started experimenting with ultrasound for surface cleaning and the emulsification of oil, because it was cheaper and reduced environmental impacts compared to conventional processing.
But more recently, researchers have begun to experiment with ultrasound to improve flavor in fruits and vegetables, through enhancements to firmness, mealiness, oil content, and acidity. It affects food molecules through a process called cavitation. When targeted with ultrasound, tiny bubbles in the liquids in foods (such as the juices in fruits and meat) collapse into centers of intense heat, pressure, and turbulence known as hotspots. These hotspots can accelerate local chemical reactions.
Some researchers are experimenting with the use of ultrasound to speed up the process of brining meat, for example, or to improve the shelf life of strawberries and raspberries. Food technologist Adil Gani, and scientists from the University of Kashmir, in India, agitated 500-gram batches of local, ripened strawberries in an ultrasound bath for periods from zero to 60 minutes and analyzed them for just over two weeks. The researchers found that ultrasound exposure lowered the potential for microbial activity. It also improved color and firmness, increased the berries’ retention of antioxidants, including vitamin C (which has also been seen in raspberries) and increased shelf life.
As Farid Chemat, a French sonochemist, and colleagues, once said: Using ultrasound with food is “one of the most promising research areas in the field of modern food engineering.”
Simran Sethi is the author of Bread, Wine, Chocolate: The Slow Loss of Foods We Love, about agricultural biodiversity and saving foods by savoring them. Follow her on Twitter @simransethi.
The lead photograph is courtesy of Sascha Erni, .rb via Flickr.