CONSISTENCY is commonly the textural property possessed by dairy products, sauces, syrups and pharmaceuticals lotions (i.e. fluid products).
It most often makes use of the back extrusion rig for its measurement. Consistency relates to the 'firmness', 'thickness' or 'viscosity' of a liquid or fluid semi-solid.
Stirring a fluid or semifluid food with a spoon or a finger is frequently used by consumers to give an indication of viscosity or consistency.
STRINGINESS/SHORTNESS is the degree (distance) to which a product hangs on the probe when the probe is withdrawn.
It is a major characteristic of mozzarella cheese or adhesives but is also commonly the textural property possessed by sauces (e.g. ketchup, dessert sauces), confectionery glazes, baked product toppings and undoubtedly, syrups.
In the adhesive industry this characteristic is sometimes referred to as 'legging' or 'tailing', as stringiness may result in the formation of filaments or threads when the adhesive surfaces are separated.
FRICTION is a phenomenon that is part of our daily lives - in one sense we would find most difficult to survive without it yet in another it can be most expensive to minimise.
It can be simply identified as the resisting force that arises when one surface slides, or tries to slide, over another. It is commonly the textural property measured from packaging materials, shaving gels, cosmetic sponges, etc.
Friction can be a limitation to us; for example, the friction of packaging can be a major limiting factor in the speed of packing machines. Additives are often used to improve the lubricity of surfaces, this is known as 'slip'. Polythene is added to packaging to improve slip characteristics.
SWELLING is associated with an increase in size or volume of a product.
Swelling applications include tablets, gels, films, pellets, mucosal tissues, super-absorbent polymers, sponges, aquaculture feed, chemical and yeast leavened products, etc.
Depending on application, swelling can be quantified by measuring changes in force or distance by either (i) compressing a product a slight distance and then measuring how force increases as the product swells, or (ii) applying and maintaining a small force onto the product and measuring the distance change as swelling occurs.
BITING/CUTTING FORCE gives an indication of the firmness/hardness of a product.
Bearing in mind that if a row of top front teeth were pulled from a
curve into a straight line they would represent a 'knife edge', using a
knife blade gives a close representation of the biting or cutting
action.
TOUGHNESS – whilst Hardness/Firmness is usually the textural property possessed by most products, the word 'toughness' or ‘chewiness’ may be substituted for a textural property more associated with the product.
TENSILE STRENGTH is the measure of the force or stress required (resistance to lengthwise
stress) to pull a sample to the point where it breaks or before
permanent deformation results.
Usually it is the maximum amount of tensile stress that it can be subjected to before failure, although the definition of failure can vary according to material type and design methodology.
In the fields of material science, mechanical engineering and structural engineering there are three typical definitions of tensile strength:
- Yield strength: the stress at which material strain changes from elastic deformation to plastic deformation, causing it to deform permanently.
- Ultimate strength: the maximum stress a material can withstand.
- Breaking strength: the stress coordinate on the stress-strain curve at the point of rupture.
SPRINGINESS is the rate at which a deformed material goes back to its undeformed condition after deforming force is removed.
It is a measurement of elastic recovery – the textural property possessed not only by baked goods such as cakes or breads but also by novel confectionery products and pharmaceutical materials (e.g. cosmetic sponges).
RUPTURE FORCE – the force that is required to produce a major break/rupture in a
sample – can be related to the firmness and brittleness of a product. It
is related to burst force – the force causing a sample to break
suddenly and violently into pieces. Rupture force measurement can be
crucial for such products as medical implants, which may be required to
resemble soft tissue but must remain intact for the duration of their
intended residence.
Several other products, such as gel capsules
containing vitamins, possess bursting as a desirable property, but must
withstand transport and handling before ultimately bursting in the
mouth.
SWELLING is associated with an increase in size or volume of a product.
