Viscosity in Food Production

GCSE: Chemistry

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Viscosity is a property of a fluid which is the measure of the fluid’s resistance to flow due to shear stress. Many think of viscosity as the ‘thickness’ of a liquid for example, water is ‘thin’ so it is known that water has a low viscosity and vice versa for ‘thicker’ liquids such as honey. Another way of explaining it is to think of fluids as consisting of different elements which move in different directions and at different rates, but which flow in the same direction. When the different elements of the fluid move past each other, friction is produced; this friction is called the viscous drag (1).
Viscosity is a very important factor in the food industry. For example, in the chocolate making industry, the viscosity of the chocolate must be perfect for highly efficient, cost effective production. The melted chocolate must flow fast enough through the pipes so time isn’t wasted when it is transported to different areas of the factory, but simultaneously it should be viscous enough to keep its structure when placed in different moulds and when coating fillings evenly during the enrobing process (3). Also, the time it will take to set (or dry) the end products, all depends on the viscosity of the chocolate. Dispensing the fluids into packaging is also viscosity dependant as this process also needs to be quick to save time and money (4).
In honey manufacture, some of the factors mentioned are taken care of. To keep the honey moving at a practical rate in the pipes, processing plants adjust equipment such as the ‘falling film evaporator,’ which is usually at a horizontal position, to an elevated position ‘in case of the horizontal system vacuum pump getting unnecessarily loaded.’ (5).
George Gabriel Stokes was an Irish-born mathematician. He devoted the majority of his professional life working on fluid properties. The most significant of his discoveries was the work describing the motion of a sphere through a viscous fluid. His work then lead to Stokes’ Law, ‘a mathematical description of the force required to move a sphere through a quiescent, viscous fluid at a specific velocity.’ (Fluid Mechanics: Stokes’ Law and Viscosity-Laboratory Investigation No. 3, Scott A. Shearer, Jeremy R. Hudson).
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