“The magic begins here,” reads the website for Ingredion, a company whose Texture Centre of Excellence helps the food industry achieve the perfect consistency for their products. Texture is big business and the science of food structure even has its own ology: food rheology.

And yet in the everyday enjoyment of eating, texture is often considered the poor relation of taste and smell (US research found that textural awareness was often subconscious). But the professionals know all too well that, while the sensory spotlight may fall on flavour when we’re savouring a mouthful, get the texture wrong and it’s game over – we’ll reject it outright.

Not only does texture have a casting vote over a food’s acceptability, it is also essential in identifying it. When researchers pureed and strained foods, young adults of normal weight were only able to identify 40.7% of them. Flavour alone is not enough.

We are incredibly sensitive to texture. Touch is of course the primary sense we use to determine it, but kinesthetics (the sense of movement and position), sound (crunch: good; squeak: bad) and sight are also involved.

We can detect ice crystals in ice cream measuring 40 microns (or 1/25th of a millimeter). Millions are spent in research and development to deter the growth of these harmless crystals. This is also why ice cream made with liquid nitrogen is so prized. It freezes so fast that the crystals are weeny, giving the creamiest mouth feel.

In his book, Food Texture and Viscosity, Concept and Measurement, Malcolm Bourne of Cornell University uses beef as an example of the vast economic implications of food’s textural quality. The tougher the cut, the cheaper it is – despite the priciest, unblemished fillet steak lacking the flavour of fattier cuts on the bone.

Bourne, who is a consultant for the food industry, says the three most relished texture notes are crispy, creamy and chewy. And food with more bite has become more popular in recent decades, he says, because dental health improvements have meant that many people keep their own teeth for most of their lives.

We have, writes Bourne in his book, a “deeply ingrained need to chew”. It starts in babyhood and continues right through to old age when, if we can afford it, we’ll throw cash and inconvenience at fixing our teeth so we may continue to chew, even though we could just as well get our nutrition from soft or pureed foods.

Gnawing is a satisfying business. It’s good for you, too. A growing body of research indicates that it increases blood flow to the brain, which helps stave off dementia. A large Swedish study last year found that old people who could chew hard foods, such as apples, had a considerably lower risk of failing mental faculties.

Food aversions are generally subjective, but there are definitely trends in unpopular textures. To the western palate, sliminess is often greeted with suspicion and associated with decay. For instance, while most people love mushrooms, they are often berated for their “slug-like” and “rubbery” texture.

Offal is another textural foe.

The most extreme textural revulsion occurs when we feel something unexpected in our mouths. If you pop in a chunk of chocolate only to find that it doesn’t melt, or you’re immersed in the wonder of a mushroom risotto and suddenly bite down on some grit, you get a rude awakening. An unsettling moment of panic that your food is rotten, or contaminated with something gross….

The Guardian: Read more

The art of rheology

By Dr Pretima Titoria, Team Leader: Ingredients, Food Innovation at Leatherhead Food RA

What consistency of dough would result in a perfect product? Why is this fromage frais not giving the right mouthfeel? Why is this low-fat butter not spreading properly? Why is this yoghurt not setting correctly? Why is this sauce not flowing the way it should? Why is this hydrocolloid mixture separating out? Why is this mayonnaise neither stable nor creamy enough? Which thickener or gelling agent should I use for this recipe?

All of these questions can be answered by the science of food rheology.

‘Rheo’ is the ancient Greek word for flow, and together with ‘logy’, it defines an area that studies the deformation and flow of matter. Thus, food rheology is about the consistency and flow behaviour of food and drinks products under specific conditions, and can provide crucial information in all aspects of food manufacture from raw materials to in-mouth behaviour.

For instance, the rheological behaviour of ingredients, such as hydrocolloids and proteins, will determine the appearance, texture and stability of the final products; the rheological behaviour of intermediate products at different stages of a manufacturing/processing line is often regarded as a quality control indicator; the rheological behaviour of the final end-products will determine the organoleptic and mouthfeel properties, and influence consumer acceptability.

Ideal for troubleshooting

Rheological studies can not only provide information on the microstructural changes occurring within a product as part of recipe reformulation, processing conditions and storage conditions, but can also be used as a troubleshooting tool to resolve problematic issues.

For instance, a product development team has been developing various recipes for a chilled fromage frais product; consumer feedback had been negative, with most of the complaints focusing on a ‘sluggy, slimy mouthfeel’. Rheological measurements of the fromage frais product, on the rheometer, showed the melting temperature to be 55°C, which was well above the oral temperature of 37°C.

This crucial piece of information steered the product development team towards reformulation of the recipe, by changing the gelling agent type and concentration, such that the melting temperature was close to that of the oral temperature, therefore resulting in a softer texture within an acceptable melting profile in-mouth.

Another example was the observation of a curry sauce dramatically thinning overnight; the recipe listed honey and starch as the main ingredients. Chemical analysis indicated the presence of amylase activity in the honey, which led to a degradation of the starch, thereby leading to the thinning of the sauce.

Rheological measurements of honey/sauce mixtures on a viscometer (Rapid Visco Analyser), whereby honey was heated to different temperatures for different periods of time prior to addition to the sauce base, led to identification of optimal thermal treatment for deactivation of the amylase enzyme in the honey. This approach led to a successful formulation of a curry sauce that was stable not only overnight, but also during the product’s shelf life.

Leatherhead’s Food Innovation Group has a dedicated laboratory equipped with a state-of-the-art controlled stress rheometer, a range of viscometers, a Rapid Visco Analyser (RVA) and a texture analyser, all of which can be used to provide detailed rheological behaviours of various ingredients, intermediate products and final products.

These techniques are often complemented with other techniques, such as microscopy, particle size measurements and differential scanning calorimetry; such a plethora of data will allow for a detailed understanding of the micro- and macro-structural properties, both of which control intermediate and final product quality.

Source: Leatherhead Food RA, July-August 2013 Newsletter