How to measure and analyse the texture of food, cosmetics, pharmaceuticals and adhesives.

Tuesday, 6 January 2015

It’s time to perform Textural Magic! Part Two

Multi textured gel balls - "caviar"Performing textural magic with
the use of texturising agents

Continuing our look at the world of Molecular Gastronomy...

Texture Trick No. 1: Spherification:
creating multi-textured gel balls

The spherification technique (created by el Bulli in 2003) consists of a controlled jellification of a liquid which forms spheres when submerged in a bath.

The sphere of liquid surrounded by a delicate membrane of jelly breaks very easily when placed in the mouth, releasing an explosion of flavour.

The spheres can be made in different sizes and have been given names like ‘caviar’ when they are small; or ‘eggs’, ‘gnocchi’ and ‘ravioli’ when they are larger. They are flexible and need to be carefully manipulated. It is possible to introduce solid elements in the sphere which will remain in suspension in the liquid, giving the possibility of introducing multiple flavours and textures in one preparation.

Just about anything can be given the appearance of balls of caviar with this trick. Sodium alginate is mixed with any liquid which is then dripped into a calcium salt and water solution. Scooped out at the optimum time, they should be jellied on the outside and still liquid in the middle as the calcium solution will set the sodium alginate gel. Fruit juices make a nice choice for spherification as you can add them to desserts for a touch of decoration. Alternatively, balls of consommé, or balsamic vinaigrette balls can be presented for an interesting savoury garnish.

Measuring Gel Strength and Rupture Force
Gel properties such as elasticity and rupture force of – for example – pectin, gelatine, agar etc. are important in the development of novel products with diverse textural differences. The strength of gels can also be utilised in products where gelling agents are added to modify the consistency of the required end product.

A common approach to gel testing is the measurement of gel strength. Whilst gelatin ‘Bloom’ has a Standard testing method, this approach can be used for any gel type [1]. A 0.5” cylinder probe (or 1” for pectin) is moved down into the gel to a distance of 4mm at which point the force is measured. If required, the probe can continue further into the gel and measure the elasticity (the distance at which the gel can be penetrated until its rupture point) and the force to rupture. Brittleness (i.e. rupture at a short penetration distance), elasticity and gel strength/rupture force measurements will give quantitative indicators of the mouthfeel of the gels.

1 - bloom jar test
Cocktail Gels

Molecular mixologists can now use laboratory equipment techniques and a range of hydrocolloids to create interesting cocktails with new textures, flavours and presentations. Cocktail gels, edible cocktails, gelée cocktails, gelatin cocktails or solid cocktails, whatever you wish to call them, if crafted correctly will delight the consumer. The success comes in making the gels sufficiently firm that they can be handled, but soft enough so the cocktail gel melts in the mouth and does not feel too rubbery.

Not only do these fascinating orbs revolutionise cocktails, they have now started to appear in all types of dishes, savoury and sweet, to add appeal.

Measuring Gel Firmness and Springiness

A measurement of both firmness and springiness (elastic recovery) of self-supporting gels can be made using a cylinder probe larger than the sample being tested. By using a 'Hold Until Time' test, a chosen compression distance is held for a chosen period of time, over which the product’s recovery is recorded. A simple calculation can be made to analyse the data and determine gel ‘springiness’.

For a more fundamental test approach, the elastic moduli can be determined by compressing cylindrical shape gel samples (fixed on sandpaper to avoid slip as shown [2]) with a larger surface area Cylinder Probe. Elastic moduli are determined from the initial parts of the stress-strain curves.

2 - gel firmness/springiness test and cocktail gel glasses
Texture Trick No. 2: Gelled Spaghetti: creating extruded pasta from gels

Agar Agar Spaghetti, also called molecular spaghetti or flavoured spaghetti, is another creation of molecular gastronomy Chef Ferran Adria and the El Bulli team. It consists of a spaghetti or noodle usually about 3 mm to 5 mm thick and 2m long made of a flavoured liquid jellified with agar agar. The agar agar spaghetti can be served cold or hot.

Measuring Bite Force and Tensile Strength

The Spaghetti/Noodle Tensile Rig [3] is well suited to perform break strength and elasticity measurements on both noodle and spaghetti-like samples. The sample is located through slots in the parallel friction rollers and then wound round two or three times to reduce any slippage and also to anchor the sample ends. The rollers ensure that the sample is not split or cut during the test and that the break occurs along the extended part of the sample.

3 - spaghetti/noodle tentile rig
Alternatively, a Light Knife Blade [4] is a Perspex blade which is used for Cutting or Bite Force tests where limited force to cut or break a sample is required. The force to cut is equivalent to the effort involved in biting with the front teeth and hence provides an easy to interpret indication of the sample’s bite force or ‘firmness when bitten into’.

4 - Light knife blade test

We can design and manufacture probes or fixtures for the TA.XTplus texture analyser that are bespoke to your sample and its specific measurement.

Once your measurement is performed, our expertise in its graphical interpretation is unparalleled. Not only can we develop the most suitable and accurate method for the testing of your sample, but we can also prepare analysis procedures that obtain the desired parameters from your curve and drop them into a spreadsheet or report designed around your requirements.

For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.

TA.XTplus texture analyser with bloom jar The
TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.

No-one understands texture analysis like we do!

To discuss your specific test requirements click here...

Watch our video about texture analysis Replicating Consumer Preferences
 Texture Analysis applications

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