Editorial Feature

How to Measure Snap, Crackle and Pop Sounds in Food

Taste, smell and texture have long been associated with eating enjoyment, but there is another characteristic that is yet to be fully explored: sound.

From the satisfying crunch of a potato chip to the energetic fix of a carbonated drink, the sound heard when a food is consumed provides vital information on its quality, both actual and assumed. Growing recognition of the intrinsic role of sound in eating enjoyment is now starting to emerge as an important trend with untapped potential and is driving a new generation of food acoustics analysis procedures designed to align product development with end-user expectations, create a positive point of difference and secure consumer loyalty.

How to Measure Snap, Crackle & Pop!

 The snap of a biscuit or crunch of a potato snack are well-known expected physical characteristics. Image Credit: Stable Micro Systems

Selling 'Texture' of your product

A number of the world’s largest food producers are now starting to commercialise the crunch of their product.  Kellogg’s believes that the crunchiness of the grain (what the consumer hears and feels in the mouth) is a key driver of the success of their cornflakes. Cheetos uses the slogan “The cheese that goes crunch!” A Doritos ad rolled out in 1989 featured Jay Leno revealing the secret ingredient: ‘crunch’. Once upon a time, Frito-Lay even conducted research to show that Doritos chips give off the loudest crack.

Where crispy, crunchy, crackly etc. are important acoustic features of a product, marketers will attempt to accentuate this salient characteristic in TV advertisements to enhance your realisation of the importance of sound to the overall enjoyment of a product. Television viewers cannot experience the taste or the smell of a product being advertised.  They can only see it and, of course, hear it. Advertising the aural assets of a food acquaints the potential customer with this most important quality attribute of many products.

If you’re thinking that this is all a bit leftfield to be of any practical use to the mainstream food industry, it might interest you to know that major food manufacturers are investing resources in this research area. 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.  Latest advances in analysis technology like the Acoustic Envelope Detector attached to a TA.XTplus Texture Analyser are now making it possible for manufacturers to extract this valuable data.

For example, A TA.XTplus Texture Analyser equipped with an Acoustic Envelope Detector to analyse acoustic emissions from different formulations of fish batter was produced by Heston Blumenthal in his TV documentary series ‘In Search of Perfection’.  So in the future, it could be that it will no longer be about patenting a secret recipe, but about patenting a crunch. In the 1980s, Kellogg’s tried to trademark the specific crackling sound made by its cornflakes. That might yet happen.

How to substantiate your product’s textural signature with a Texture Analyser

10% more spreadable, 20% crispier, 10% less sticky – all of these quantitative claims need to be substantiated.

Once product developers have formulated a winning ‘noisy’ food product the aim would be to ensure the consistency of this signature quality of the product during manufacture. Every brand knows that importance of consumer loyalty lies in the consistency of their product quality, be it flavour, appearance or texture. So, the measurement of a product’s acoustic signature is key to determining the gold standard product ‘noise’ for the purpose of quality control of all future batches of the product. When Unilever changed the formulation of their Magnum ice cream chocolate coating the distinctive sound of the coating was lost and consumers complained. It turned out that this was a signature feature of the product experience and this reaction resulted in the return to the original formulation to put back the distinctive solid cracking sound every time one of their consumers bites into this distinctive ice cream bar. So, if consumers perceive a crisp that crunches louder as being better, this presumably means that if manufacturers can turn up the volume on product crunchiness, they are more likely to attract loyal consumers.

But how do you know when you’ve hit the ideal crunch volume? One way is to use a trained tasting panel to determine whether the crunch is loud enough. Another, more repeatable, reliable and scientific approach is to use a Texture Analyser – an instrument which measures sensory attributes of a product by capturing force, distance and time data at a rate of up to 2000 points per second coupled with an Acoustic Envelope Detector.

How to Measure Snap, Crackle & Pop!

Three point bend rig produces force data (black) and acoustic data (red) from a typical test on a cereal bar. Image Credit: Stable Micro Systems

If a product developer wanted to make their product crunch louder, they would need to test the product on the Texture Analyser using an appropriate fixture – so, for a biscuit, they would use a three-point-bending rig. They would then position the microphone 1 centimetre from where the biscuits were going to fracture. The acoustic data would then be captured throughout the breaking of the biscuit and would be presented graphically, as a jagged line with some taller peaks. 

To make a louder product you would be looking for the product that generates the highest ‘peaks’ or decibel values, so tall peaks rather than lots of little ones. If a manufacturer wants to compare how crispy different products are, they can count the number of peaks generated and divide this by the number of seconds over which they occur. This will tell how many fractures are produced in a second – and the more there are, the crispier the product.

What can a potential consumer learn from these sounds? First, the listener-viewer can determine the extent or intensity of crispness and/or crunchiness. They determine this by noting the total amount of sound produced in a given biting distance.  A relatively large proportion of high-pitched sounds indicate the product is crispy. A larger proportion of lower-pitched sounds means the product is crunchier.

When a crisp food is broken or crushed characteristic sounds are produced due to the brittle fracture of the cell walls. Since cracks propagate at very high speeds (too high for even high speed cameras) the sound is produced in a very short space of time – i.e. as a pulse. Slowed down and plotted onto a graph, the pulses can be seen as a series of tall peaks, but actually last only for milliseconds. The more peaks, the crispier it is – it's as simple as that. These sounds (acoustic emission) have been used to try to quantify sensory crispness. Sounds from crisp foods differ from those of non-crisp foods primarily in their loudness. Crisper products would produce louder noise – amplitude is one of the variables that distinguishes more crisp from less crisp sounds. This is used in combination with the number of sounds (frequency) produced within a given distance or time.

How to Measure Snap, Crackle & Pop!

Force (top curve) and Acoustic Energy Emissions (lower curve) against time for a breakfast cereal. Image Credit: Stable Micro Systems

Measuring other Sounds:

Whilst much of the work to date has focussed on the measurement of crispness of brittle foods, other examples of products that have both a Physical and Auditory Expectation include:

  • The ‘Spray’ of a can (whilst measuring its actuation force)
  • The ‘Burst’ of bubbles in an aerated dessert
  • The ‘Bite’ of an apple (whilst measuring the force to puncture its skin)
  • The ‘Crack’ of a chocolate coating (whilst measuring the force to crack)
  • The ‘Snap’ of spaghetti (whilst measuring the break)
  • The ‘Click’ of a switch (whilst measuring the actuation force)
  • The ‘Snap’ of a pencil (whilst measuring the break strength)
  • The ‘Fizz’ of a bath bomb (whilst measuring the hardness)
  • The ‘Squeak’ of Halloumi cheese (whilst measuring the bite force)    

For a full summary of how an Acoustic Envelope Detector can be employed to measure snap, crackle and pop:

Acoustics - the fourth dimension in Texture Analysis

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