In both food science and the food industry, the importance of viscosity cannot be overstated. This parameter is extremely important in terms of both quality control and the design of the process. It has an impact on a variety of operations, including pumping, packaging, and mixing, among others. It is also a fundamental factor that affects food consumption, as it is a characteristic of food texture, it plays an important role in the perception of flavor, and it even has implications for health and safety in processes such as digestion and deglutition.
A fluid will flow in response to an external force or stress being applied to it, which will cause the fluid to experience internal friction that will fight against the flow. Therefore, the internal friction of a fluid, also known as its capacity to resist flow, is what is meant to be understood when referring to viscosity.
When a fluid is thought of as consisting of a number of laminar layers, the formula that describes the fluid's viscosity is simple and can be expressed in centipois (cP) or Pascal seconds (Pa s):
The shear rate is the relation of speed between two laminar layers of fluid, whereas the shear stress is the force per area that is required to move a laminar layer of fluid. This holds true only for Newtonian fluids, like water, whose viscosity is not affected by changes in shear rate up to a certain temperature. Other fluids, like oil, have viscosities that are sensitive to changes in shear rate. However, the vast majority of fluids do not behave in this manner; these fluids are referred to as non-Newtonian, and the viscosity of these fluids must be measured using a different set of criteria. It is recommended that additional reading be done in order to gain a more in-depth understanding of these phenomena and its implications.
If you were to compare a fluid with a higher viscosity to one with a lower viscosity, you would notice that the former moves more slowly and has a more opaque appearance. This quality is extremely dependant on the fundamental properties of a substance, such as its molecular composition, solute concentration, structural organization, and density. In addition, viscosity should not be thought of as an absolute value but rather as a function of external factors such as temperature, shear, and pressure. These are the kinds of factors that influence viscosity and, as a result, the technological and organoleptic properties of a food product.
What exactly is a viscometer, then?
Any device that is utilized in the process of determining the viscosity of a fluid is referred to as a digital viscosity meter or viscosimeter. Other classes of instruments, known as rheometers, are capable of determining viscosity under a variety of flow conditions, in contrast to these types of instruments, which are only capable of measuring viscosity under a single flow condition. Viscometers are the instrument of choice for production and quality control applications because of their affordability, portability, ease of operation, and ability to provide faster determinations. However, viscometers are less versatile and precise than other measuring devices.
How does a viscometer work?
The determination of a fluid's viscosity can be accomplished using a variety of methods, including those in which the measuring object remains still while the fluid moves through it, as well as those in which the fluid remains still while the measuring object moves through it. In either scenario, the flow conditions have to be kept on the laminar regime as much as possible.6Because of the drag that is caused by the relative motion of the fluid and the surfaces of the measuring object, it is possible to determine the viscosity of the fluid. There are several different types of viscometers, each of which can be defined in terms of their relative motion, their geometry, their accuracies, and the applications that they are intended for. There are two distinct ways to express viscosity, which are referred to as absolute viscosity and kinematic viscosity respectively when discussing the various viscometry methodologies. The absolute or dynamic viscosity of a fluid is measured by observing how much resistance it exhibits to flow when subjected to a controlled external force. On the other hand, the kinematic viscosity of a fluid is measured by observing how well it flows when subjected to the force of gravity. The density of the fluid must be taken into consideration in order to convert between these two methods of expressing viscosity. Either the kinematic viscosity must be multiplied by the density of the fluid in order to obtain the absolute viscosity, or the absolute viscosity must be divided by the density in order to obtain the kinematic viscosity.
The operation of these instruments is based on the calculation of the amount of time required for a predetermined volume of fluid to travel through a capillary at a predetermined temperature. Due to the straightforward nature of their operation and straightforward design, they are good alternatives for performing routine measurements and quality control. However, they can only be used in liquids with a low viscosity and no solid particles in suspension. Because of this, their applications are limited to liquid ingredients and beverages.