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.

Chip/Fries Firmness 

As fruit and vegetables are natural they have inherent variability which usually compromises the repeatability when testing single pieces. For this reason, the firmness of chips or French Fries can be determined using a Multiple Chip Rig. 

This rig measures the force obtained by the penetration of a multiple sample of chips. Up to 10 chips can be tested at any one time and the rig ensures that each chip is completely penetrated by a 2mm diameter probe. 

The probe head has a fast release adapter to enable the probe to be rapidly cleaned and relocated in the same position. Two adjustable stainless steel rods are used to hold the samples in position on the sample holder. 

A typical curve produced from this test is shown below highlighting the area calculation which is used for comparison purposes.

Determining the Presence of a "Crust"

With the use of frying as home food preparation technique in the U.S. dropping 22% over the past five years, according to a Food Marketing Institute report, and sales of French fries falling in restaurants for eight consecutive years, finding alternative ways to add crispness and crunch to foods is a very big idea.

Cooking in oil is widely used in the production of snack foods of various kinds, and results in drastic changes to the structure of the food. Penetration of oil is particularly important for structure development in products such as potato chips, tortilla chips and potato crisps. In products which become totally hard and crisp, the oil first coats the surface and begins to move into the chip. 

As the heat builds up inside, moisture turns to steam and exits the chip, leaving a sponge-like network of tunnels which fill with oil. This process occurs within the first 20 seconds of frying. Starch granules gelatinise inside the chip, but not at the surface. The interior becomes smooth and plastic as protein, starch and lipids interact to form a continuous phase which hardens upon dehydration. 

In products with a soft interior, such as potato chips, the dehydrated oil-infused layer is confined to the peripheral four or five layers of cells. The hard crisp surface pellicle (or crust) develops at the same time as the interior of the chip is changed to a structure comparable to that produced by moist heat. 

A penetration test using a small cylinder probe can be used to puncture the sample and indicate the presence (or absence) of a distinct crust. Such a "crust" would be highlighted by much higher penetration forces than the force required to penetrate through the underlying potato tissue.

Crispiness of Potato Chips/Crisps

The assessment of potato crisp/chip crispiness is perhaps the most dominant characteristic and can greatly affect consumer acceptability. A sample possessing a crispy texture produces a curve featuring multiple force peaks. This type of curve (as shown below) can be analysed using Special Calculation features in Exponent software.

Firmness of Potato Salad and "Mash"

Thermal treatment is one of the most important processes in the manufacture of storable and ready-to-serve food products of agricultural origin. During thermal treatment, many desirable and undesirable reactions take place; components such as vitamins and colour components, for example, and also physical properties, such as texture, may be changed.
 
A suitable test to monitor effects of processing time of e.g. potato salad preparation, or effects of changing quantities of additional ingredients for e.g. "mash", is to use an Ottawa Cell (as shown right). 

A typical curve obtained from the testing of mashed potato using an Ottawa Cell is also shown below and highlights a plateau region obtained during the extrusion test. 

The measurement of the mean force obtained over this plateau region and an area calculation are most often recorded as indicators of texture differences between batches, changing formulation or modification in processing parameters.




Watch the video below to see a summary of the types of testing possibilities that are available for the measurement of fruit and vegetable texture to provide quality control tools and ultimately, consumer satisfaction:

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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.

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!

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