Thursday, 11 February 2016

Controlling the brittle texture of biscuits

Snappy to soft? The bakery spectrum

Bakery products have specific anticipated textures, and staling can change this expectation quickly and dramatically. Products which are expected to be hard - go soft - and vice versa. 

Baked shortbread texture quality

The texture of shortbread can be measured to predict snapping
Baked goods which fracture when fresh
Foods that are homogeneous particulate solids, when fresh, should be crisp and crunchy, with a brittle texture that allows snapping and breaking … biscuits, crackers, breadsticks, also crispbreads, rice cakes, oat cakes, muesli bars / granola / cereal bars - and shortbread. Their ideal behaviour is to fracture. Other, similar, baked goods are preferably flexible to a certain degree - cookies, flapjacks and gingerbread - should break, but only after exhibiting some bend and softness: this proves they are fresh.
For a product like shortbread, there is a desirable brittleness, enabling snap.
What factors affect the ability to be snapped? And by how much?
Is "snap" measurable? And so can it be controlled?
The FTC TMS texture analyzer system can test shortbread snap.

Sensory theory

Food texture can be scientifically classified by a number of contributory mechanical attributes: hardness, cohesiveness, viscosity, springiness, adhesiveness, fracturability, chewiness and gumminess.
A consumer may describe the sensory quality of food with different terms, for example: crunchy, crisp, soft, firm, fresh or stale. For hard, crunchy, bakery product, its snapping characteristic conveys freshness and provides crunchiness.
A texture analyzer enables the measurement of attributes which reflect the consumer’s experience by simulating the interaction: Compression, extrusion, shear, tension, penetration, bend and break.
Bending - to break - is the representative method for the simulation of a consumer flexing the product between the fingers and snapping it into smaller pieces.

The practical science

measuring the peak bend to break force correlates to a brittle texture quality
A 3-point bend snap fixture simulates consumer bite and break
Fracturability is best tested by a snap, bend and break method. The texture analyzer is fitted with the TMS lightweight 3-point bend fixture. The shortbread's snap strength is calculated from the peak force, and we also measure the work from the area under the resulting curve. The test procedure will lower the crosshead to a distance that guarantees the shortbread will be fractured.
The three anvils are tipped with rollers, to minimize friction and allow pure bending, with minimal shear. The sample is placed across and supported by the two lower anvils. The upper blade-shaped anvil is lowered onto the center of the product, causing it to either flex initially, or snap with little deformation.

Quantitative results

For a brittle bakery product, we would expect a steep rise in compressive force over a very small displacement, followed by a rapid fall-off as the sample undergoes a single massive failure. Stale products would undergo some level of flexure, and potentially a less instantaneous break.
Reversed characteristics would be valuable for products which are desired to exhibit a limited, controlled amount of flexure, and which conversely snap when stale. The hardness (and so firmness or softness attributes) in flexible products may also be tested by other texture analysis methods: compression, penetration, shear or tension...

Bakery industry benefits

Penetration, compression and shear can also test certain textures for bakery items
Fresh/stale snap force comparison graphs and other bakery tests 
With an accurate and repeatable texture analysis capability, the producer of brittle, friable and flexible baked goods can confidently measure the effect of changes to ingredients, formulation and preparation, and make recommendations for packaging and storage…
For example, shortening is the significant ingredient in achieving a softness of texture in mouth-feel, but not at the expense of crispness and fracturability. Biscuits often have design details, from simple perforations to more decorative shapes, which could make the biscuit more fragile in transit. The packaging must protect the product, intact, until the customer is ready to snap it.
A texture analyzer enables objective, quantified evaluation of sensory characteristics, for an accurate and repeatable way to control the perceived quality of the product - to control shortbread snap.

See the video here.