From the satisfying crunch of a potato chip to the energetic fizz of a carbonated drink, the sound heard when a food is consumed provides vital information on its quality, both actual and assumed. It may seem surprising that this aspect has had relatively little attention in terms of food analysis.

According to Charles Spence, professor of experimental psychology at Oxford University and author of a new study examining sound and flavour perception, it is the forgotten flavour sense with untapped potential. In fact, growing recognition of the intrinsic role of sound in eating enjoyment now looks set to emerge as an important trend.

It is driving a new generation of food acoustics analysis designed to align product development with end-user expectations, create a positive point of difference and secure consumer loyalty. As such, manufacturers have identified a growing number of texture-related attributes that influence the appeal of a product, including crunchiness, hardness and crispness, to name but a few.

APPEALING ACOUSTICS

When a cereal bar, cracker or hard fruit is crushed, it releases acoustic energy from the brittle fracture of the cell walls. Naturally, these sounds (acoustic emissions) differ between products. For example, a relatively large proportion of high-pitched sounds indicate a product is crispy, wheras the equivalent ratio of lower-pitched sounds would mean it is crunchy. Equally important to measure is volume or amplitude the louder the noise, the greater the crispness for example.

By analysing the unique characteristic of each product, manufacturers can gain a greater understanding of overall performance and make any necessary changes to improve texture. This may lead to alterations to the ingredients or machinery in manufactured products, and for fresh produce, changes to the handling or packaging processes may be identified.

once product developers have formulated a winning noise for a food product, the aim is to ensure consistency during manufacturing. Therefore, the measurement of a products acoustic signature is also key to determining the gold standard and ensuring quality control of all future batches.

EMERGING TECHNOLOGY

Although texture analysis is well established across the food sector, until recently the same could not be said for measuring acoustics. Traditionally seen as unreliable and inaccurate, instruments designed specifically to evaluate sound were also incompatible with existing analysis equipment.

The latest acoustics technology addresses these concerns and offers manufacturers a number of important advantages:

• Discrimination: unwanted background noise can be ignored. Sophisticated equipment can distinguish between sounds emitted from the product and mechanically generated noise; only the relevant acoustic emissions are recorded.
• Synchronisation: force and sound profi les from individual tests can be synchronised and the resulting curves analysed simultaneously. The relationship between acoustic and force events can then be easily identified.
• Automation: the tests themselves and sound acquisition can be handled automatically by software incorporated into sophisticated texture analysis instrumentation. This saves time, facilitates use and increases accuracy.
• Convenience: data can be saved in smaller fi les to aid the interpretation of test results. Earlier methods of acoustic data collection have often produced large, unmanageable files.

A VISUAL ADVANTAGE

While the measurement of acoustic data is emerging as a test method in its own right, the most meaningful results are gained when this is carried out and analysed alongside traditional texture information. Recently launched texture analysers feature advanced software designed to record acoustic data at the same time as other texture information for greater synergy and a more detailed evaluation of a products rheological properties.

One of the most exciting innovations in this area combines acoustic analysis with synchronised video playback. Capturing acoustic tests on video provides a much greater understanding than sound alone—our eyes miss important details which can be reviewed by slowing the recording down. If conventional data in the form of force-distance-time is recorded simultaneously, a much greater understanding of the interplay between texture and sound can be achieved.

In practice, this integrated approach allows manufacturers to look at a force-distance-time graph alongside a corresponding frame-by-frame video. As the instrument begins collecting data, a signal is relayed to the video capture interface which activates recording. When replayed later, each frame is automatically synchronised with the data points on the force-time graph; allowing slow replay of those frames and potentially picking up a significant event which may not have been seen by the naked eye.

This visual advantage is particularly relevant for products with uneven textures or which break quickly in a complex manner. Some types of bread, for example, have a range of textures; the crust, the main body of the bread and crumbs are all different and each component produces its own event. This new approach also improves the accuracy of results which is a valuable advantage for food products which, unlike other test materials, have a shelf-life and can vary over time.

Fruit and vegetables, for example, may go soft and limp in the laboratory between experiments. Their texture changes, meaning later tests may not be accurate. Using synchronised visual and graphical data, irregularities in test results can be more easily identified without the need for re-evaluation. This eliminates misleading information, facilitates interpretation of test data and introduces a new dimension in food analysis for even greater accuracy.

ACOUSTICS IN ACTION

once a specific auditory cue has been identified as a core product characteristic, it is vital that consistency is monitored and maintained. Integration with texture information is the key and the resulting data can be used to enhance existing products or develop new concepts.

A carbonated drink, for example, is judged partly on the sounds of effervescence and bubbles popping in the glass. Make the fizz louder or the bubbles pop more frequently and perception of the quality of the beverage may go up. If manufacturers are using a texture analyser for product testing, these important sounds can be measured at the same time to build a detailed picture of the multi-sensory experience.

Halloumi cheese is also a useful case in point. The squeaky noise heard when it is bitten into has become a strong auditory cue and an expectation. Due to a phenomenon known as stick-slip, this frictional feature can be readily measured by a standard texture analyser, so it makes sense to measure the acoustic component of this quality at the same time.

By expanding the scope of analysis in this way, manufacturers can also measure and evaluate performance of a product against its competitors and so ensure positive differentiation.

SOUNDS LIKE THE NEXT BIG THING

Food and drink is obviously a multi-sensory experience but the focus is shifting to fully explore the potential benefits of encouraging consumers to eat with their ears. Mr Spence believes it could be the next big trend in food, with modern chefs leading the way.

In fact, world famous experiential British chef, Heston Blumenthal, has built his reputation on the belief that "eating is the only thing we do that involves all the senses"; as quoted on the menu of his Fat Duck restaurant. He put this ambition into practice back in 1997 when he introduced his now legendary seafood dish Sounds of the Sea, which was served along with an iPod playing the sound of breaking waves. A literal interpretation perhaps, but the idea of using sound as part of the eating experience is now attracting attention from the wider community of influential modern chefs as well as marketers and big brands.

Unilever, for example, is quoted in Spences research to highlight the importance of signature sound to brand value. The global giant reformulated the ice cream for its premium Magnum brand to stop it falling off in pieces, only to discover that losing the distinctive crack as the chocolate is broken with the first bite was an even greater disappointment for consumers – this element was naturally reinstated.

With so much activity and innovation in this area, manufacturers would be wise to keep their ears open for the latest developments.