Food crunch releases ultrasound

08/02/06 In a unique double discovery, researchers at the University of Leeds have shown that massive bursts of ultrasound are generated during the first second of biting into crunchy food – and are simultaneously analysed by the ears and mouth.

Food physicist Professor Malcolm Povey explains: “Food is, in effect, talking to us and we innately understand what it’s saying about texture by interpreting the sensations through our ears and mouths. Our research shows that the sound and feel of food in the mouth is as important as taste, look and smell in deciding whether we like something or not.

”Using a microphone, an acoustic microscope, some simple software and an enviable supply of different biscuits, Professor Povey realised that the energy produced by the very first crack of a biscuit breaking is released as distinct pulses of ultrasound – sound waves beyond the range of human hearing. Slowed down and plotted onto a graph, the pulses can be seen as a series of tall peaks, but actually last only for milliseconds and are generated at frequency levels more usually associated with bats, whales and dolphins for echolocation.

“It’s a good job we can’t hear all the energy in these pulses,” says Povey, “as they would damage our ears if we did. They’re enormously loud bangs – often way beyond safe decibel levels.”

The discovery of recordable ultrasound pulses is expected to be of great interest to the food manufacturers, who in the pursuit of the perfect crispy/crunchy texture for their products, employ an army of trained tasting panels. These people form the crux of manufacturers’ efforts at product consistency and quality control in terms of creating the optimum texture for a product.

The technique of recording the sound of biting or breaking crispy food and simply counting the peaks of soundwaves provides a cheap, quantifiable and accurate analysis of texture, that will ensure absolute product consistency: “The more peaks, the crispier it is – it’s as simple as that,” says Povey.

The research also demonstrates that the human mouth is extremely accurate in its innate analysis of these ultrasound pulses. Test results show a very high correlation to the machine-measured results by both professional tasters working in the food industry and untrained volunteers. “We had no idea that the human ears and mouth were so adept at capturing and analysing this information, especially in the space of milliseconds; it’s incredible,” he says.

“We’re not trying to replace tasting panels,” he insists, “in fact we need them to calibrate the instruments. But a machine-measured test is a quick and simple way to check consistency of products once the desired texture for a product has been decided. However, the research does suggest that the training of food tasters in respect of measuring crispness is probably unnecessary.”

Povey is convinced that the same ultrasound measuring techniques could potentially be applied to other textures in food manufacturing as well as having major applications outside the food industry.“Essentially our methods measure what happens when a material fails,” explains Povey.

“So this technique could easily be transferred to industry to detect failures in materials used in engineering or the aerospace industry, for instance.“

Materials testing usually requires expensive equipment, but we’ve proved that recording, measuring and comparing sound pulses is rigorous and accurate. In the same way engineers used to tap wheels on railway engines to listen for faults, we can use these microphones to record a much wider frequency range to pick up tiny defects. Its potential is enormous.”