Physical Property Measurement: Fracture Testing in Bending

This is a versatile test and can be applied to many types of products that are available in, or can be cut or shaped into, elongated test beams. 

The most conventional method is a three-point bend test in which the specimen is supported horizontally at either end like a bridge and a probe moving downwards bends it in the centre. As the specimen bends it stores up strain energy, which is dissipated in cracking at the point of fracture.

Physical Property Measurement: Fracture Testing by Compression

Compression tests can be carried out on a wide variety of products that experience such a force in natural conditions. 

These may include fruit and vegetables, puffed cereals, cakes and biscuits, confectionery and pharmaceuticals. 

Normally, as these products may be oddly shaped, a compressive test is the most reliable way of assessing their fracture behaviour.

Physical Property Measurement: Fracture Testing in Tension

Many foods and pharmaceuticals are not normally subject to tensile forces in their manufacture and consumption. There are, however, exceptions, e.g. dough, gels, spaghetti and adhesives. 

These tests can also be performed on materials from which elongated test specimens can be cut and gripped within the clamps of the Texture Analyser to be stretched. This could include fruit, vegetables and meat. In any case this type of test yields reliable results for tensile modulus, yield stress and strain, strength and strain to fracture, and, if the crack area can be measured, the fracture toughness of the material.

Physical Property Measurement: Types of Fracture

Fracture is simply crack propagation. Force has to be exerted to initiate a crack, then energy has to be supplied to propagate it. This is the energy that goes into breaking the bonds within the material in order to generate new surfaces. 

There are three ways a crack can propagate within a material. All structural failures are the result of material failure in one of these three modes.

Physical Property Measurement: Introduction to Fracture

What is Fracture? This is the first of a set of blog posts on the subject of fracture testing. Traditional information on fracture testing focusses on techniques for assessing engineering materials using standard methods and strict geometries. However, these may not be so useful for the typical user of a Texture Analyser.

The loosest definition of fracture is “a form of failure in which the material separates into two or more pieces due to an applied load”. Fracture strength is the stress at which a specimen fails or fractures. Fracture can be brittle, ductile or semi-ductile. This refers to the nature of deformation and will be covered in the next post.

Measuring Food Quality with a Texture Analyser

More than ever before, the food industry is finding itself forced, through outside pressures, to improve constantly its product quality and to maintain that quality at a consistently high level. Food quality is an important concept, because the foods people choose depend largely on quality.

Consumer preference is important to the food manufacturer, who wants to gain as wide a share of the market for the product as possible. Quality is difficult to define precisely, but it refers to the degree of excellence of a food and includes all the characteristics of a food that are significant, and that make the food acceptable.

Texture: The Final Frontier of Food Science?

Back in February, Kendra Pierre-Louis of Popular Science wrote this interesting article.  

She indicated that ‘Tweaking texture could give us healthy versions of our favourite junk foods—and that's just the beginning.’

She talks about how she has embraced culinary novelties such as glass potato chips, grilled whale and poisonous shark but cannot stomach the sensation of hollandaise sauce.

Food Texture – Likes and Dislikes

Apart from crispy foods like crackling, British consumers embrace softer-feeling food.  Industrialised, processed food is often marketed as soft and creamy in the UK, with adverts for such foods playing on the sensual and comfort associations that have set in from a young age.

Our childhood association with pureed food is one of the reasons we turn to soups when we are ill.

The Vocabulary of Food Texture

The chef Mario Batali says that the single word “crispy” will sell a restaurant dish quicker than any number of clever adjectives. 

Picture “aubergines” on a menu. You might hesitate to order them, fearing they would be flaccid or oily, as they so often are. Now think how much more appealing “crispy aubergines” sound. “Crispy” makes everything appear as safe and crunchy as chips.

The word’s universal appeal is a sign of how much we are governed by texture in what we eat. Yet we hardly seem to mention it (unlike in China, where many foods, from fungus to tripe, are prized for texture alone).

Food Texture around the World

Gristly, gelatinous, bony textures, say in pig's ears or bird's feet, are usually shunned in the UK, whilst goose intestines, sea cucumbers, chickens' feet and ducks' tongues are just some of the fiddly, gelatinous, gristly dishes that are regarded as delicacies. 

In China, kou gan (meaning "mouth-feel") is highly celebrated and texture in these dishes means everything. In Victorian cookery books, whole birds and the feet of animals were celebrated with relish, while in other parts of the world, such as China, foods enjoyed purely for their challenging textural pleasure are highly prized.

The Desire to Chew

There’s more to chewing than you might think. It’s arguably the first digestive activity that we bring to a meal, and unlike the chemical processes that occur in our gut, chewing falls under our conscious control. 

But chewing is more than a digestive aid. It also has a potent psychological function that helps keep body, mind and emotions in balance, according to The Institute for the Psychology of Eating.

Sensory Analysis and Definitions of Food Texture

The process of sensory evaluation starts with a well trained sensory panel – a group of humans who will judge sensory qualities. 

To carry out a meaningful texture profile analysis, a panel of judges needs to have knowledge of the texture classification system, the use of standard rating scales and the correct procedures related to the mechanics of testing. Panellist training should start with a clear definition of each attribute.

Sensory Analysis vs. Texture Analysis

Sensory analysis includes use of the senses of smell, taste, sound and touch.

Evaluation of food, pharmaceutical and cosmetic texture by touch includes the use of thefingers, as well as the lips, tongue, palate and teeth in the mouth.

When producing products for consumers, manufacturers endeavour to offer products with a defined uniformly high quality. As would be expected, sensory methods of analysis are subject to wide variability, are labour intensive and therefore expensive. Alongside sensory tests of products by trained tester panels, instrumental measuring methods are used as flanking measures.

The Importance of Texture in Food

Take gummy mashed potatoes, leathery dried apples, and limp celery. We spurn them all, because their texture – the way they feel on the tongue, lips, hard palate, or teeth – is offputting.

Most people obsess over the flavour of everything from ice cream to chocolate – but the professionals, food scientists and chefs alike, know that crispiness, creaminess and chewiness is just as important. Texture is big business and the science of food structure even has its own 'ology': food rheology.

Why Measure Texture?

Texture analysis is the mechanical testing of food, cosmetics, pharmaceuticals, adhesives and other consumer products in order to measure their physical properties.  

It is an important attribute in that it affects processing and handling, influences habits, and affects shelf-life and consumer acceptance of products.

Because of its adaptability, texture analysis has become commonplace in many industries to measure a specific or range of characteristics or properties relating to the way a material behaves, breaks, flows, sticks, bends, etc. Typical texture and physical properties than can be measured include: crispiness, stickiness, brittleness, spreadability, chewiness, firmness and consistency.

What is Food Texture and How is It Measured?

Texture refers to those qualities of a food that can be felt with the fingers, tongue, palate, or teeth. 

Foods have different textures, such as crisp crackers or potato chips, crunchy celery, hard candy, tender steaks, chewy chocolate chip cookies and sticky toffee, to name but a few.


Texture is also an index of quality. The texture of a food can change as it is stored, for various reasons. If fruits or vegetables lose water during storage, they wilt or lose their turgor pressure, and a crisp apple becomes unacceptable and leathery on the outside.

Testing Products with a Crust, Skin or Multilayers

Products with a crust, skin or multilayers bring textural variety to a product. The breaking of the skin of an apple when bitten into or the biting through the layers of the perfect pastry product brings a textural sensation that is highly desirable and anticipated. Failure to notice a difference in the layers of such products brings disappointment.

The collection of detail of a thin, brittle, laminated or multi-phased structure is best performed with a small diameter probe or thin, sharp fixture. A larger probe such as a platen, cylinder or sphere will give bulk compressive properties but will not resolve the properties of each layer. It is beneficial to penetrate the sample slowly in most cases to give a larger time gap between fracture or puncture events so they can be more easily identified.

How to test the Physical Properties of Thin Samples

Thin samples are notoriously difficult to test. This is a short guide with some tips to make your thin sample testing more accurate and repeatable.

Compression or penetration

When testing the hardness of thin products by compression or penetration, the measured force may show a sudden exponential increase as shown in the graph below. This occurs as a result of the probe moving nearer to the base. 

Either the test will abort because the load cell has overloaded, or the test will finish, collecting irrelevant data that does not reflect the true properties of the product. Comparison could then incorrectly be made between maximum forces that are not sample derived.

Implications of spreadability for dairy and bakery products

The spreadability of margarine and butter is of paramount importance for consumer acceptability. It is a physical property and results from the fact that these products consist of a dispersion of solid fat crystals in liquid oil.

The ratio of solid to liquid fat in a product is probably the most important factor determining hardness and spreadability. However, hardness and softness are not the only factors influencing spreadability; smoothness and brittleness are also important. 

Temperature-Controlled Texture Analysis of Fats and Oils

Fats and oils perform a key role in defining the sensory characteristics of our favourite prepared foods. They affect the structure, stability, flavour, shelf-life, palatability, mouthfeel and visual appearance of food products.

For manufacturers to obtain the desired performance, it is important to recognise that different applications require a fat or oil product with different physical and organoleptic properties. 

Substantiate your product claims with the aid of texture analysis

Customers are wary of manufacturers using taglines to tempt them into buying their product – a conditioner that states “hair three times suppler after first use” will not sell well if customers start using it and find no difference to their tresses. 
 
News travels fast these days with thousands of cosmetics review sites and online shops, and products that fail to live up to their claims will be given poor marks. The manufacturers could have performed a simple bend test on hair specimens treated with their conditioner and would have found their mistake before it was too late. 

The development of methods to measure the effect of cosmetics is driven by increasing pressure on cosmetic companies to provide solid evidence to support product claims.

New Food Texture Trends at IFT

The 2017 exhibition for the Institute of Food Technologists was held in Las Vegas, Nevada, from June 25th to 28th, showcasing thousands of developments in the food technology industry.

The show gives a good reflection of the current wants and desires of consumers, and they seem to be asking quite a lot from manufacturers this year. One major area to consider while keeping up with these trends is food texture. The majority of attendees were heavily aware of the importance of texture measurement in R&D as well as its maintenance in quality control; texture is such an important quality of food and beverage products that many manufacturers mention a textural attribute specifically by name on a product’s packaging or even in the name itself.

Toast your Roast with Texture Analysis

Variations on ‘Roast Dinner’ are eaten for different occasions all over the world – a roast joint of meat, potatoes, vegetables and gravy, often followed by a stodgy pudding such as an apple pie.

This is a meal that consumers look forward to so it is important that the texture of each component is no less than perfect. This analysis would be carried out for the purpose of calculating ideal cooking times, in the case of a supermarket or a chain restaurant, or to test the quality of supplied ingredients.

Texture Analysis – Time for Tea!

Texture Analysers are made in the South of England, where afternoon tea stacked high on a triple tiered cake stand is a staple for any big celebration.  

Our customers around the world may be surprised to find some items here that aren’t so different from their own national food.

The first component of afternoon tea is a large, fluffy scone, cut in half and spread with sticky jam and clotted cream. There are regional arguments for whether jam or cream should be applied first, but in both cases cream and jam that are hard and difficult to spread cause the scone to break up under the knife, which is very undesirable. The softness of the inside of a scone can be assessed by preparing a cubic sample, having cut the crusts off, and performing a compression test with a large cylinder probe. A soft sample will yield under a low force.

The Perfect Texture of Lunch

A sandwich, a bag of crisps and a can of soda – the lunch eaten by millions of people around the world every day.

They are not aware of the meticulous testing that has gone into every stage of their meal, from the packaging down to the wheat flour used to make their bread. It is no surprise that food manufacturers focus so much of their effort into tailoring these items so they are a perfect compromise between cost and quality, to be pleasing to the customer but not expensive to manufacture.

Texture Analysis of your Breakfast

A satisfying breakfast sets you up for the rest of the day. It is often composed of many different components, each with a different texture, and there are many variations around the world.

An example of a widely-consumed breakfast is the “continental breakfast”, comprising of bread, cold meat, cheese, yoghurt, fruit and cereal. Regarding texture, bread should be resilient (brittleness in bread suggests staleness), ham and salami should be tender, and breakfast cheese may be soft.

Texture tricks – using Hydrocolloids to create Textural Sensations

Texture is magical. The way a food “feels” affects the way we perceive its appearance, aroma and taste. 

And while manipulation of mouthfeel can seem mysterious, many tricks can help developers create and maintain the perfect texture – be it real or illusion. The following excerpts are from an original article written by R. J. Foster, and is a gem for those interested in the incorporation of hydrocolloids and their effect on texture. 

The texture effect  
Consumers rely on texture as an indicator for many different qualities of the foods they eat. Some textures might imply a lack of freshness: carrots that are soft or limp, bread that is hard, or a stick of chewing gum that crumbles...

Texture Analysis in Sports Nutrition – Hydrating and maintaining hydration with hydrotabs

Low Tolerance Powder Compaction test of a tablet
using the TA.XTplus Texture Analyser

Hydrotabs are specifically designed sports rehydration tablets that ensure fast hydration during intense exercise. 

These quickly dissolved tablets are packed with electrolytes and are high in sodium (and usually containing other electrolytes) to further promote the hydration process.

Compact solution
Many products are produced in powder format and then compressed into tablets. Powder compaction is an essential step in the manufacturing process and it is essential to avoid products cracking during processing. 

Their liability to failure is influenced by the powder’s processing properties, such as density variations introduced during die filling and/or compaction. 

The characterisation of powder in its bulk format can enable manufacturers to predict the behaviour of the powder when compressed; however, the need for more targeted analysis of powder compaction has been identified and, as a result, the Powder Compaction Rig was developed. 

Measuring Indulgent Cosmetic Textures

If you have ever bought a cosmetic product from a make-up stand in a department store, you will have experienced a sales pitch from someone trying to tempt you into buying the product. 
 
You may have noticed that colour and fragrance are mentioned, but these are secondary to texture (and of course efficacy) – “this lipstick is creamy and feels moisturising all day”, “this face cream is thick and velvety”, “this lipgloss won’t make your lips feel sticky”, “this face wash gives you a luxurious lather”. 

You will not see this written on the side of cheap cosmetics, whose manufacturers think of texture as a last resort as they do not have the time or funding to carry out the required research.

Texture Analysis of Food in Vogue

Today, things are rather different in the food market from the produce that was available a few decades ago. 
 
While some familiar flavours and textures endure, the market is now defined by a constant stream of new flavours and textures allowing the food product development universe to expand in every direction.

Product development teams are seeing a new landscape of possibilities and behind this is growing consumer adventurousness. The broadening appetite for new flavours and textures stems from the exposure consumers now have to diverse food and drink cultures created by increased mobility, prosperity and the media-rich world. Younger consumers in particular are keen to seek out new flavours and textures and represent such an important target segment in this booming area of food product development.

New method for measuring Unconfined Yield Strength of Powder using your existing Texture Analyser

Stable Micro Systems have launched the Unconfined Yield Stress Rig for the measurement of powder flowability.

In industries that handle powders on a regular basis it is very important to understand how a powder or granular material responds to pressure. In storage, the weight of powder in a container exerts pressure on the particles at the bottom. If the powder has good flow behaviour it will not consolidate and will flow out of the silo or hopper without sticking – this is very desirable. The longer a powder is stored for, the more likely it is to form a cake in its hopper and refuse to flow without further assistance.

Using Novelty Gels in New Food Product Development

Choosing the optimum texture analysis test method to measure your new texture creations

Exciting new food textures will be among the emerging trends over the next three years, together with more ‘playful’ products for adults and more widespread use of edible packaging, according to a leading food futurologist.

Successful chefs have realised that to be at the top of their game they need to create new culinary experiences using a combination of unusual tastes, textures and theatrical twists to give the eating experience a new multi-sensory dimension. This is enabled by a variety of new high-tech equipment, adjusted traditional preparation techniques and a handful of clever chemicals. The myriad of gelling ingredients available to formulate such texturally amazing products is endless which means there is virtually no limit to the vast variety of food products that can be configured.

Physical Analysis: Putting Cosmetics Packaging to the Test

The development of cosmetics for release into a competitive market is a high cost endeavour, so it would be inefficient for these high stakes products to be shipped in low quality packaging, or for the container to degrade during its shelf life.

Packaging is the first thing the customer sees in the shop so from this point of view the graphics and physical design are important to make it stand out amongst other similar products; the appearance of packages can directly affect marketing. However, the main purpose of packaging is to ensure the product arrives in a customer’s hands in perfect condition and to prevent any losses caused by shipping, handling or storage.

Testing packaging pouch performance

Stand-up flexible pouches are in vogue all over the world and according to experts are set to experience high growth in the future, too.

There are many reasons for this. They are attractive to consumers and easy to handle to transport, for instance. They were very much led by the squeezable baby fruit sauce packages but now when we observe the retail food shelves, we see ketchup, mayonnaise, wine, salsa, honey, juice, premixed cocktails, and a host of fluid food products in stand-up flexible pouches.

Hosiery put to the test!

A pair of tights is usually put on with a certain amount of stretching, and fingernails or jewellery often snags on a single thread that will turn into a run or “ladder” once the leg is applying stress to the tights. 

Additionally, a ladder may be caused during the working day, such as a snag occurring when the tights are pushed against the underside of a desk. This can greatly inconvenience the wearer as it appears unprofessional and they may not have a spare pair. It can also be expensive.

The Importance of Texture Analysis in Cosmetic Stability Testing

Cosmetics companies! Can you say with confidence that a product your customer buys in bulk today will have the same excellent qualities they expect from your brand when they open it in six months’ time?

If not, you need to start stability testing, pronto.

Stability testing is simply the assessment of the lasting power of a cosmetic, during which samples of it are put under different environmental conditions for a set time period, and its properties analysed. These conditions vary in light, temperature, pressure and humidity levels and are designed to imitate what the product may be subjected to during its lifetime.

Texture Analysis of Surimi Products: 3: Elasticity

Shellfish has a characteristically chewy texture; to create a convincing comminuted product, manufacturers need to imitate this. 

In texture analysis terms, chewiness is measured by elasticity. High elasticity produces an item with a rubbery consistency (Figure 7) whereas low elasticity creates an undesirably brittle product.

Texture Analysis of Surimi Products: 2: Toughness – Measurement using Cutting/Shearing Tests

Preparation processes can detrimentally affect the texture of imitation shell-fish products and affect repeat purchase decisions. 

During new product development manufacturers must consider the effect of these processes on the structure of surimi with regard to toughness. 

Texture Analysis of Surimi Products: 1: Introduction; Gel Strength (Stiffness)

A predominant ingredient in the Orient is fish – used both fresh and comminuted as surimi fish mince.

Made for centuries by the Japanese and thought to date as far back as 1100AD, surimi is now spreading from Japanese to Western processed foods and is used to form extruded, shaped or cooked simulated shell-fish meat products such as crab, lobster, scallop or shrimp.

To gain consumer acceptance of imitation shell-fish, the texture, flavour and appearance of fresh shell-fish must be matched as closely as possible. This has successfully been achieved by Japanese processors who produce surimi as an economic alternative to fresh fillets and imitation shell-fish which are barely distinguishable from the real thing. 

Physical Analysis: Putting Cosmetics to the Test

A customer walks into a pharmacy looking for a new cream to keep their hands soft. They don’t have much to go by other than packaging and price, so they choose the same brand they use on their face. 

They get outside and squeeze some out of the tube with their normal pressure, and their palm fills up with too much thin, watery cream that seems to do nothing to remove the dryness. A disappointed customer, and the very reason the cosmetics company should have used physical analysis on their cream before they released it for sale.

Chips, Crisps & Mash – Getting the Texture Right!

Potatoes are a common, even basic, vegetable in Western diets, in some cases assuming the status of a staple.

Potato snack foods include French Fries and dried miniature versions of them (chips in the US sense, or crisps in UK) in many flavours. They appear as mashed potato in many convenience meals such as TV dinners, and as potato salads in take-away meals.

Adding Texture to Tea

The best discoveries are total accidents, and bubble tea is no exception. 

The drink as we know it today found its origins in Taiwan in 1988 when Lin Hsiu Hui, a product developer in a tea house, decided on a whim to pour her tapioca pudding into her iced tea. 

Perhaps excited by the extra level of texture she had incorporated into her drink, she passed it around the meeting room and it was met with acclaim; the product was tweaked and brought onto the market, and its sales rocketed. 

Texture Analysis in the Nailcare Industry: 5: Tensile properties of nail wraps

Self-adhesive nail wraps can be tricky to fit to the nail. To avoid ripples in the surface, the film must be flexible enough to be smoothed into small corners but also taut across the surface of the nail. 

The wrap must also be tough enough to avoid tearing during application and have a reasonable strength. All these properties can be assessed using a tensile test. 

Texture Analysis in the Nailcare Industry: 4: Adhesive properties of nail wraps

Nail wraps are flexible adhesive films that are smoothed onto the nail’s surface and trimmed. 

They provide an opportunity for intricate designs that can be printed by the manufacturer that would otherwise be difficult to paint by hand. 

The design will be consistent across all nails and removes the difficulty of using the non-dominant hand to paint.

Texture Analysis in the Nailcare Industry: 3: Mechanical properties of dry polish

A manicure is subject to a lot of abuse as the wearer goes about their daily life (opening jars, cooking, typing on a keyboard). 

For repeat purchase of a nail polish, it must be able to stand up to this type of use. As well as the adhesion properties mentioned above, the stiffness and toughness of a polish are all extremely important. 

An overly stiff, brittle polish would be undesirable as it would break when a nail is bent when opening a soda can, for example. The low stiffness is important for the polish to follow the nail as it bends. A high strain to failure is also crucial, or the polish film would break under the slightest deformation.

Texture Analysis in the Nailcare Industry: 2: Nail polish drying time

Nail polish has been developed to have a faster drying time with brands claiming “dry in 60 seconds” or “quickdry”. 

However, smudging a manicure is still a common complaint. There are also difficulties accelerating the drying time of more natural polishes containing fewer volatile solvents. New products must be tested for this in a consistent way.

Texture Analysis in the Nailcare Industry: 1: Introduction

The way we look and feel is more important than ever in the age of constant selfie-taking and the abundance of cameras at every social gathering.

This is not to mention the impossible beauty standards set by photoshopped billboards and magazine shoots that ordinary people feel they have to live up to. 

It is no surprise that cosmetics are more popular than ever, with the global cosmetic market estimated to reach US$675 billion by 2020. 

Application advice - comparing cutting/shearing accessories

We are often asked why there are so many different blade fixture options available from Stable Micro Systems.  

Our range of blades vary considerably in size, material, thickness and sharpness. In general they are used to measure the Bite/Cutting Force of products which in some instances can relate to their ‘Toughness’. The following guidelines may help in clarifying the potential use of each.

Substituting your Meat at mealtimes: Part 8: Sliced meat and Quorn – texture comparison

Sliced meat: how does it hold together?
 
How a sliced meat or meat substitute holds together is an important textural expectation of the consumer. The binding characteristics of the sliced product can be greatly affected by its formulation and processing thus affecting its tensile strength.

Whilst tensile grips or pneumatic grips are the traditional choice for tensile testing there are alternatives for a soft and thin product such as sliced meat. A Film Support Rig (shown in Figure 16) is designed to hold small amounts of thin or film-like material in a drum configuration in order to measure the biextensional properties of the films using a puncture test. 

Substituting your Meat at mealtimes: Part 7: Meatballs and nuggets – texture comparison

Despite the simplicity of penetration tests when faced with a non-homogeneous product, penetration is highly compromised as a smaller surface area for measurement is also more sensitive to variations in sample structure and low reproducibility and misleading data is obtained. 

Results may show a wide variance between maximum and minimum forces depending on whether the probe meets with, for example, internal structure variation such as is usually present in meat products.