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February 2006

Malcolm Povey

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 Envelope Detector from Stable Micro Systems, 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.”

Update: This research has attracted a great deal of media interest. Including articles in The Guardian, Metro, Yorkshire Post, and an amusing piece from the Yorkshire Evening Post.


Notes for editors

1. Professor Povey’s research 'Acoustic envelope detector for crispness of biscuits' has been published in the Journal of Texture Studies (2005) 

2. The dynamic range of human hearing is approximately 110 decibels. Prolonged exposure to signals over 90 dB can cause permanent hearing damage. 

3. The human ear can nominally hear sounds in the range 20 Hz to 16 kHz. This upper limit tends to decrease with age, most adults being unable to hear above 16kHz. Ultrasound frequencies start in the range beyond 16kHz. The ear itself does not respond to frequencies below 20Hz, but these can be perceived via the body's sense of touch. The frequency range covered by Professor Povey’s equipment reaches 220kHz.

4. Professor Povey is a co-inventor of the Ultra Cane, commercialised through the University spinout company Sound Foresight Ltd. The device uses ultrasound waves which are felt by the user through the cane’s handle to navigate around objects and provide more accurate spatial awareness for the visually impaired.



Stable Micro Systems' Acoustic Envelope Detector provides a quick and easy method of collecting and analysing the noise released by crunchy products as they are deformed.

Stable Micro Systems is proving that texture analysis is not just for technologists after the use of its Acoustic Envelope Detector by top biscuit manufacturer Bahlsen has sparked massive media interest.

The biscuit company has been inundated with visits from leading media companies NDR, dpa, ddp, RTL, SAT 1 and 3 Sat following an article published in news magazine Spiegel detailing tests conducted by Bahlsen to analyse the 'crunch' made by its products. As consumers perceive a sharp, crisp sound emitted when biting into a biscuit to indicate its freshness, Bahlsen has been using Stable Micro Systems' acoustic emissions measurement technology as a key part of product development and quality control.

Interest in the testing carried out by Bahlsen's research and development team has resulted in regional, national and even international media coverage, spanning print, radio, television and the internet. As well as interviews with R & D Manager Heinz-Dieter Lechte, the activity has included filming of the tests as they are performed on Bahlsen's famous biscuits at the company's headquarters in Hanover.

Stable Micro Systems' Acoustic Envelope Detector is used in conjunction with the company's TA.XTplus texture analyser to quickly and easily analyse acoustic emissions and quantify product texture. A highly sensitive directional microphone acquires the acoustic data while the texture analyser itself measures force, distance and time as the biscuit breaks. The procedure gives Bahlsen the confidence that the sounds emitted by its products will maximise consumer appeal.

Ralf Winopal from Winopal Forschungsbedarf GmbH, Stable Micro Systems' distributor in Germany, said: "Texture analysis has become essential for product development and quality control. The media interest in Bahlsen and the Acoustic Envelope Detector shows that everyone, from scientists and technologists to the general public, can get excited by it."



Figure 1:  ADM Milling measures dough extensibility using a Kieffer Dough & Gluten Extensibility Rig on the TA.XTplus.

As the largest independent flour miller in the UK, ADM Milling has been supplying the bakery and food manufacturing sectors with high quality flours and flour-based blends since 1999. Processing around one million tonnes of wheat per annum, the company supplies customers ranging from multinational manufacturers to in-store bakeries, caterers and craft bakers across the UK and Republic of Ireland.

Operating in this dynamic market, with a broad customer base and high volumes, quality flour is crucial. Accurate, reliable QC systems are therefore a prerequisite. With this in mind, ADM Milling recently upgraded its texture analysis equipment - a key part of the quality control process. This has enabled the company to benefit from the flexibility to design tests which investigate specific parameters of interest, as well as improved data processing.

Upgrading for more precise analysis

The new generation instrument from Stable Micro Systems, the TA.XTplus, replaced the existing TA.XT2i texture analyser in place at the company. ADM Milling requires accurate measurement data on the performance of its flours in three key areas; dough extensibility, bread firmness and pasta texture. The new instrumentation not only fulfills these requirements but also delivers the added benefit of allowing the company to develop its own unique test procedures.

Dough extensibility

Dough extensibility is an important measurement in bakery for pre-determining the rise qualities and structure of the finished product which can be affected by homogenisation, long relaxation times or the addition of salts, emulsifiers and oxidants. Using the Kieffer Dough & Gluten Extensibility Rig attachment (see Figure 1) on the TA.XTplus, the dough's resistance to extension (maximum force) and extensibility (distance to break) are measured. Samples are divided into identical test sections which are left to relax and then laid onto a grooved plate. This is then placed into a spring-loaded clamp secured to the texture analyser. When the tensile test commences, a hook probe rises, extending the dough sample until it breaks.

Figure 2:  ADM Milling measures the firmness and stickiness of cooked pasta on the TA.XTplus.

Test results reveal that different varieties of wheat have a markedly different effect on dough extensibility. Using the TA.XTplus therefore allows ADM Milling to determine which kinds of wheat are best suited for different types of flour and, therefore, different end-products. For example, a bread-making dough requires a great deal of extensibility, whereas this would be a negative attribute for biscuits.

Bread firmness

Measuring bread firmness is another important consideration for ADM Milling. As consumers become more selective in their choice of products and often perceive softer bread to be fresher, manufacturers are increasingly looking for the highest quality flour to provide them with optimum results. Bread firmness analysis using the TA.XTplus forms an essential part of the company's ongoing monitoring of its products, with tests performed weekly to ensure that any changes in grist or processing do not adversely affect the high quality of its flours. This enables ADM Milling to guarantee consistency for its customers.

Standard firmness tests involve a flat, circular plate being lowered onto a sample slice of bread, which is then compressed while a load cell contained in the texture analyser's horizontal arm measures the force. With the upgrade to the TA.XTplus, Stable Micro Systems' proprietary software, Exponent, has enabled ADM Milling to develop a specially designed test method to also analyse the recovery of bread after initial testing. Once the standard test is complete, the probe is lowered once more to measure the height of the sample following compression. This is compared to the height immediately before compression to indicate the recovery of the bread, which would typically stand at around 97%.

This additional testing provides ADM Milling with data which gives a more complete description of loaf texture, as it allows the company to also establish the resilience of the slice. This is important in terms of how well the loaf would withstand the spreading of butter, for example, or whether it would stick to the roof of the mouth. Using this specially-designed test, ADM Milling can establish exactly what proportions of ingredients are needed to create a top quality loaf with high recovery. This property is affected by the inclusion of different additives, such as enzymes or improvers, or the use of different wheat varieties, which affect crumb texture. This is an example of the unique test procedures facilitated by the TA.XTplus.

Pasta texture

ADM Milling also tests pasta firmness and stickiness. Using Stable Micro Systems' pasta firmness / stickiness rig, strands or sheets of pasta are held on the TA.XTplus by a support block which includes a rectangular cut-out exposing the sample (see Figure 2). A corresponding rectangular compression plate, connected to the loadcell, is lowered to test the firmness of the pasta during the compression stroke, and its stickiness upon withdrawal.

The company recently adapted this test method in order to investigate specific parameters of interest to a customer, which wished to develop a firmer noodle. By analysing the textural effect of changes to the grist and processes, ADM Milling has been able to make recipe and process suggestions to increase the firmness of the product.

The ability to devise tests according to customers' needs is regarded as a key advantage of the upgrade by ADM Milling. The company is now able help customers effectively manage changes to processes or ingredients and also to solve problems, such as decreasing the rate of staling of products.

Technological advantages

ADM Milling found the facility to design testing programs to suit specific requirements a key advantage, while the improved software interface of the TA.XTplus is easy to use. Information such as capacity, calibration and serial numbers is also stored within the load cell and automatically detected upon installation, providing greater flexibility for the design of unique test procedures.

Improved data processing is also an important benefit. Data from each test can be recorded and interpreted with ease using Stable Micro Systems' 32-bit software, which provides consistently accurate and quantifiable textural information. This has allowed the company to benefit from the following:

The company is also able to take full advantage of the new flexibility offered by the texture analyser's improved electronics and mechanics. It now has the ability to programme individual arm-movement sequences at various speeds and distances. This enables the most complex test protocols to be established and allows exact measurements to be achieved. The new speed range of 0.01mm/s to 40mm/s on the TA.XTplus is also broader than the 0.1mm/s to 10mm/s range on the TA.XT2i instrumentation and ensures that all tests carried out could more closely mimic real-life performance. This enables more exact results and precise product analysis to be obtained.

Support from start to finish

ADM Milling worked closely with Stable Micro Systems to ensure a smooth hand-over during the upgrade and to integrate the TA.XTplus with its existing IT systems. As well as taking advantage of user training and technical advice, so staff could use the new system quickly and accurately, the company also receives ongoing support from Stable Micro Systems. It can download new firmware to the TA.XTplus from www.stablemicrosystems.com, which provides ongoing modifications and improvements to the software. ADM Milling can also take advantage of program and macro writing offered by Stable Micro Systems, should the company need a new test sequence or data analysis technique to be prepared.

According to John Cottrell, ADM Milling's Technical Director, upgrading to the TA.XTplus has brought tangible benefits to the company:

"We have had a great deal of experience with Stable Micro Systems' texture analysis equipment and have always been confident that it has provided us with objective and repeatable testing, and accurate, reliable results. The new generation instrumentation is even more efficient and, thanks to the facility to allow us to develop our own test procedures and improved data processing, has allowed us to achieve a real technological advantage in flour development.

"As a business we see Stable Micro Systems' protocol as essential in upholding our own rigorous quality standards. The TA.XTplus has enabled us to fully investigate the performance of our flours for a wide range of parameters and has increased our understanding of the complex role of flour in a large number of products. It also allows us to monitor our flours and ensure the consistent end-product quality demanded by manufacturers and consumers alike."

ADM Milling is a wholly owned subsidiary of the US company Archer Daniels Midland (ADM). It has ten wheat flour mills located around the UK and a technical centre in Avonmouth near Bristol. Using state-of-the-art milling technology to manufacture its products, it has earned a reputation as a highly technical miller.



Warbutons bread firmness assessment

In 1870, a British couple opened a grocery shop in Bolton, Lancashire. Reacting to a downturn in the grocery trade in 1876, Ellen Warburton started baking her own bread at the rear of the shop. The first batch sold out within an hour.  125 years later, Warburtons is the UK's largest independent baking business, employing over 3000 people at 10 bakeries and nine depots. Despite enormous production volumes, quality remains the cornerstone of Warburtons' philosophy.

Like most quality control departments in the food industry, Warburtons has relied on subjective quality testing for many years. Using a scoring system, samples taken from production lines were manually pressed to assess their softness.  Interestingly, however, this method was not used in conjunction with taste testing, which can provide a useful organoleptic profile of a product.

This manual procedure, while offering an indication of texture, fell short of Warburtons' requirements. It was not unusual for two assessors to score the same sample differently, and there were considerable problems defining "soft", and where the line was drawn between "soft" and "hard". According to Sue Thompson, Warburtons' Product Assessment Coordinator, differences between samples were especially problematic. "Sometimes we had two products which both seemed to be soft enough to pass the QA test, but we simply couldn't measure those small differences in texture which can make a product acceptable or unacceptable to a consumer. We needed an objective, reliable and repeatable way of measuring softness so that we could be confident of our assessments."

Texture Analysis of bread

In light of this, Warburtons purchased a TA.XT2i texture analyser, supplied by Stable Micro Systems. "We can now detect minute differences in the texture of our products and alter the recipe or baking process accordingly," comments Stuart Jones, Quality Control Manager.

The softness/hardness tests now performed on the majority of Warburtons' product range are well-established and easy to carry out and understand. A flat, circular plate compresses the sample while a loadcell contained in the texture analyser's horizontal arm measures the force required to perform the compression test. As the test is performed, the proprietary software, Texture Expert Exceed, gathers the information and displays it, in real time, as a graph, which can be used for further data analysis.

Furthermore, decisions about the selection of new raw materials are now strongly influenced by their effect on the finished product's texture. The effects of fats, bakery improvers, emulsifiers and stabilisers and any other proposed new ingredients can be quickly and accurately measured: and if they do not improve the end product noticeably, they are not added.

Stuart Jones sums up: "There's a lot of talk about quality in the food industry now, and no manufacturer can afford to ignore it. We believe that keeping up quality standards is essential to our future, in terms of customer loyalty, market share, sales and profits. Texture analysis is now so advanced that we are able to perfect every aspect of our recipes, production, packaging and transport without the inconsistency or subjectivity of relying only on manual testing."




D/R Dough Inflation System performs constant strain inflation

Temperature chamber allows constant strain inflation at elevated temperatures

Baking is about bubbles: the size, distribution, growth and failure of these bubbles during proof and baking has a major impact on the final quality of the bread in terms of both appearance (texture) and final volume. During proof and baking these bubbles slowly expand, producing a large increase in volume. In order for the bubbles to grow, the surrounding matrix must retain gas (CO2) for long enough to allow a considerable amount of expansion before the structure is set by baking.

The limit of expansion of these bubbles is related directly to their stability, due to coalescence and the eventual loss of gas when the bubbles burst. The rheological properties of the bubble walls will be important in maintaining stability against premature failure during baking. Conventional dynamic rheological tests carried out in shear under small deformation and high strain rates are inappropriate to baking, because they are carried out at rates and conditions very different from those experienced by the dough during baking expansion, and these sort of tests have not been able to predict the baking quality of different flours of varying quality. In terms of deformation, the relevant conditions around an expanding bubble wall during breadmaking are biaxial extension, large strains and low strain rates at elevated temperatures.


Work at Reading University has shown that the stability of failure in single dough bubble walls is related directly to the extensional strain hardening properties of the dough, and that strain hardening plays an important role in the stabilisation of bubble walls during baking.  We are evaluating rheological methods to predict breadmaking performance using a modified bubble inflation technique, developed by Stable Micro Systems Ltd., Godalming, UK, called the D/R Dough Inflation System which measures the extensional rheological properties of dough and gluten in biaxial extension under conditions of deformation, strain rate and elevated temperatures relevant to breadmaking. The latest version of the instrument (TA.XTplus) has the option of continuously variable speed, which allows tests to be performed at constant strain rates and higher temperatures more relevant to proof and baking conditions. In the previous method, bubble inflation tests were limited to a fixed rate of inflation, and both strain and strain rate varied during the test.  Because dough is viscoelastic, its rheological properties vary with both stain and strain rate. Therefore it is necessary to separate out the effects of strain and strain rate by keeping one constant while varying the other.

In the new dough inflation test strain is varied and measured as the bubble inflates, and by continuously changing the speed at which the bubble is inflated, strain rate is kept constant.

Strain hardening measured at 50°C and constant strain rate for a number of commercial flours of varying quality using the new TA.XTplus system is shown related to commercial breadmaking performance. This clearly shows that a strain hardening value of around 1.2 discriminates well between flours of poor to moderate quality and those considered to be good and excellent.

Email: b.dobraszczyk@reading.ac.uk

Results of Constant Strain Inflation of Dough




Testing the firmness of the whole fruit allows the manufacturer to predict its ability to withstand further processing

Sias carries out back extrusion tests 
on processed strawberries

Fruit texture analysis

A needle probe is used to measure the firmness of fruit skins and give an indication of their ripeness

Sias Foods is a major producer of fruit preparations for yoghurts, desserts, such as trifles, mousses, pies and ice cream for the British market. The parent company, £450 million French group Sias MPA, has manufacturing facilities all over Europe, including the UK, France, Germany, Italy, Austria, Poland and Czech Republic. Sias also operates factories in Asia Pacific, the US, South Africa, Mexico and Latin America.

The UK factory, based in Corby, Northamptonshire, processes dozens of fruit varieties. Quality control is an integral part of the production process and one of the priorities for the company's customers in the dairy and dessert industries. Of particular importance was the consistency of the fruit after processing. Two years ago, Sias' management team identified the need to further improve quality control procedures and contacted Stable Micro Systems, a leading provider of texture analysis instruments to the food industry.

The need for objectivity

Sias had previously relied on organoleptic testing by its quality control team. Whilst of significant value to any food processor, human taste panels have limited value - primarily because of their subjectivity. But in order to ensure continuity and repeatability of tests, Sias wanted to install equipment that would carry out texture analysis measurements objectively. The results of these tests could then be used in conjunction with, and as a complement to, organoleptic analysers to provide a fuller and more accurate profile of the fruit's textural characteristics.

Sias evaluated several systems, and installed Stable Micro Systems' TA.XT2i in late 1998, selected for its accuracy and the potential to perform a wide variety of tests on just one machine.

Texture analysis - improving quality

Although the original aim of installing the texture analyser was end product testing, Sias is now also using it in new product development. Having identified the ideal consistency for an apple puree for example, it may be possible to develop a blackcurrant product with a similar viscosity and mouthfeel. Steven Smallwood, Sias NPD Manager, comments: "Each year, different fruits come into fashion and we could find ourselves handling fruits we haven't processed before.  Using texture analysis enables us to quickly assess how a new fruit will process, and adjust equipment or procedures accordingly, without wasting time or money."

Testing can be carried out at any stage of the production process - from the incoming raw materials (whole fresh fruits) to the finished product. Because fruits need to be handled with care, particularly before processing begins, carrying out texture analysis tests throughout manufacture enables users to monitor their condition - the timing and degree of breakdown of structure - and could help to identify which processing methods best maintain the integrity of the fruit.

The fruit, the whole fruit

The 'back extrusion' test is a simple but valuable tool for measuring not only the consistency of a fruit preparation, but also of whole fruit pieces after processing. For Sias, the objective was to measure the firmness of the fruit in order to predict its ability to withstand further processing, normally at the dairy or dessert manufacturer's factory. A defined protocol is adhered to, in order to minimise the risk of distorting test results. After production, samples are removed and washed. Sias only tests whole fruit pieces rather than damaged ones, which by definition, have been shown to be relatively weak. Every batch of finished product is tested using the back extrusion technique.

The sample is placed in a transparent plastic vessel with a 50mm internal diameter and then compressed using a disc of an appropriate size. The choice of disc will depend on the size of the fruit pieces in the preparation. As the disc descends, the sample is forced up and around its edge and data is captured throughout - normally at a rate of about 200 points per second.

Tangible benefits

Since automated texture analysis began at Sias the quality control department has been able to test thousands of batches of fruit preparation accurately. Results have been recorded and used to define acceptable fruit hardness parameters, further tightening quality standards and providing objective analyses to complement ongoing human taste testing.

Further fruit tests

The back extrusion test is one of a number of texture analysis techniques which can be employed in fruit processing factories. These include:

Fruit hardness

The ripeness and freshness of a fruit are often defined by their firmness, particularly their skin. Using a needle probe, a fruit's skin strength (or yield point) can be measured. Alternatively, spherical probes, carrying out indentation tests, provide valuable information on a fruit's surface hardness. A simple cutting test, or Volodkevich Bite Jaws, which simulate a biting action, can measure the force required to 'bite' through the product.  Indentation and cutting tests can also be conducted on processed fruits.

Fruit preparation consistency

Back extrusion tests can be used to measure the viscosity of finished furit preparations as well as the fruit pieces within them. Forward extrusion also gives useful information on the products consistency by forcing it down through a hole in the base of the sample container. Stable Micro Systems provides containers with outlets with various diameters to suit different applications. Properties such as firmness, visco-elastic creep, and stickiness can all be assessed using a simple cylinder probe test.

Easy integration, a competitive advantage

Because texture analysis is so flexible, it can be used throughout the food industry to test ingredients as well as finished products. Stable Micro Systems stresses that it should not be viewed as a substitute for human taste testing, but as a complement to it.

As Hido Malic, Sias quality and development manager, comments: 'Installing the texture analyser was a simple way of upgrading our quality control procedures. Organoleptic testing remains very important, but the TA.XT2i is now an integral part of the process. Our customers can be confident of consistently high quality, and that obviously brings great benefits to the business.' Texture analysis has brough tangiable benefits to Sias and other major European food processors by improving quality, reducing rejected product and saving time.


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