October 3, 2023

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The Viscometer and Its Position within the Meals and Beverage Business

16 min read

Viscosity performs a decisive function in meals science and the meals {industry}. This parameter is an important in high quality keep an eye on and procedure design, affecting operations reminiscent of stirring and homogenization, pumping and packaging amongst others.1 It’s also a elementary issue affecting meals intake, being feature of meals texture,2 taking part in a very powerful function in taste belief or even having well being and protection implications in processes reminiscent of deglutition and digestion.3

On this article, we can imagine what viscosity is, how it’s measured and the packages of viscometry within the meals and beverage {industry}.

When a drive or pressure is carried out to a fluid, it flows, leading to inner friction that resists the float. Subsequently, viscosity is outlined as the inner friction of a fluid, or in different phrases, its capability to withstand float.

Taking into account a fluid as quite a lot of laminar layers, the system describing viscosity is simple, being represented in centipois (cP) or Pascal seconds (Pa s):

The shear pressure is the drive in keeping with house had to transfer a laminar layer of fluid, while the shear charge is the relation of pace between two laminar layers of fluid. That is simplest legitimate for Newtonian fluids, the place at a definite temperature, the viscosity would stay consistent as a serve as of adjustments in shear charge (e.g., water). Then again, nearly all of fluids don’t behave this manner, being referred to as non-Newtonian, and other concerns are required to measure their viscosity. For a closer figuring out of those phenomena and its implications, further studying is really useful.1

In sensible phrases, a fluid with the next viscosity would float extra slowly and seem thicker than a fluid with decrease viscosity (Determine 1). This belongings is extremely dependent at the intrinsic traits of a subject material reminiscent of molecular composition, solute focus, structural group and density. Moreover, viscosity will have to now not be perceived as an absolute worth, however somewhat a serve as of exterior components reminiscent of temperature, shear and force, all of which have an effect on viscosity, and thus, the technological and organoleptic homes of a meals product.

Fluids pouring into beakers showing that, over a set time (indicated by a stop watch), more of a lower viscosity fluid (right) will flow than the higher viscosity fluid (left)

Determine 1: Glide comparability of a high-viscosity fluid (left) and a low-viscosity fluid (proper) on the similar temperature.

A viscometer, or viscosimeter, is any tool used to measure the viscosity of a fluid.4 A majority of these tools simplest measure viscosity below one float situation, opposite to different categories of tools which are in a position to decide viscosity below various float prerequisites, referred to as rheometers. Even supposing viscometers are thought to be much less flexible and exact, they’re less expensive, moveable, more uncomplicated to function and supply quicker determinations, making them first selection in manufacturing and high quality keep an eye on packages.5

How does a viscometer paintings?

Viscosity determinations can also be carried out in line with quite a lot of strategies, the place the measuring object remains desk bound and the fluid passes via it, or the fluid is desk bound and the measuring object moved via it. In both case, the float prerequisites should be maintained at the laminar regime.6 The relative movement between the fluid and the surfaces of the measuring object reasons drag, permitting viscosity to be measured. In keeping with the relative movement and geometry of the apparatus, various kinds of viscometer, in addition to their accuracies and goal packages can also be outlined. Taking into account the other viscometry methodologies, there are two distinct tactics to precise viscosity, absolute viscosity or kinematic viscosity. Absolutely the or dynamic viscosity is decided through looking at the fluid’s resistance to float below a managed exterior drive, whilst the kinematic viscosity is decided through looking at the fluid’s float below the motion of gravity.1 Those two tactics of expressing viscosity can also be interconverted through making an allowance for the fluid’s density, multiplying the kinematic viscosity through the density of the fluid to acquire absolutely the viscosity, or dividing absolutely the viscosity through the density to acquire the kinematic viscosity.

Commonplace varieties of viscometers

–          Capillary viscometer and float cups (orifice viscometers)

The operating idea of those tools is in line with the choice of the time wanted for the standard quantity of fluid to go via a capillary. The straightforward design and easy operation lead them to just right possible choices for regimen measurements and high quality keep an eye on. But, they’re restricted to low viscosity liquids with out forged debris in suspension, which restricts their usage to drinks and liquid substances. One of the vital commonplace configurations is the “U” form capillary of the Ostwald viscometer offered in Determine 2A. Those tools are most often operated in a thermally-stabilized tub and after the higher bulb is stuffed with the fluid, the time wanted for the fluid to go throughout the marks is recorded and multiplied through an tool consistent to determine the kinematic viscosity of the fluid.2 The time it takes for the fluid to go throughout the capillary tube is immediately proportional to the dynamic viscosity and inversely proportional to the density of the fluid. Any other easy configuration of a capillary viscometer is the float cup or orifice sort viscometer (Determine 2B). This apparatus encompass a reservoir and orifice or capillary, and works through figuring out the time it takes for the fluid to go throughout the orifice.7 Those tools are reasonable, smooth to function and flexible, then again they aren’t correct as they don’t make sure that consistent force at the orifice.

Diagram of an Ostwald viscometer (left), a flow cup (center) and tube viscometer (right).

Determine 2: Diagram of an Ostwald viscometer (A), a float cup (B) and tube viscometer (C).

Pressurized variations of the capillary and float cup viscometers can be utilized so as to take care of a continuing force all over the dimension and to function below excessive pressures, enabling their usage for extremely viscous fluids. In such circumstances, the fluid is moved through fuel force or through a piston that may be precipitated through a weight or a riding motor.

In the similar class of capillary viscometers, tube viscometers (Determine 2C) use a horizontal tube fed through a pressurized tank to decide viscosity.2 In those tools, the force is decided at other positions alongside the tube, and the force drop at a particular float charge is used to calculate the resistance to float, and thus the viscosity. Tube viscometers are particularly fitted to online determinations and continuously utilized in commercial amenities.

–          Falling piston viscometers

The falling piston viscometer makes use of a piston to displace a fluid in a cylinder or container. As soon as the cylinder is stuffed with the check fluid, the piston drops below the motion of gravity, displacing the fluid throughout the gaps between the piston and the cylinder (Determine 3), inflicting a shearing impact.8 Via measuring the piston’s falling time, pattern viscosity can also be decided. The facility to keep an eye on the shear charges, through converting the piston’s mass, makes this apparatus appropriate to signify fluids desirous about excessive shear charge operations. Those tools also are smooth to function and take care of, providing an extended product lifestyles. The principle problem is that efficiency for non-homogeneous samples, reminiscent of particulate suspensions, could also be impaired.

Diagram of a falling piston viscometer, with red arrows indicating the displacement of sample up the sides of the piston.

Determine 3: Diagram of a falling piston viscometer.

–          Falling ball viscometers/rolling ball viscometers

A falling ball or a rolling ball viscometer measures the rolling/falling time of a ball via a fluid contained in a tube, as gravity acts as the motive force.2 The inclination might range from a vertical configuration (between 80° and 90°), permitting a unfastened fall of the ball, thus being designated a falling ball viscometer, or susceptible (between 80° and 10°), designated rolling ball. The time wanted for the ball to descend a decided distance is immediately proportional to the fluid’s viscosity (Determine 4). The variables concerned within the dimension are the fluid density, the ball density, the duration and time of the ball motion and its terminal pace. Those tools are smartly fitted to measuring Newtonian fluids, are smooth to function and may also be simply improvised in a laboratory. The adjustment of the attitude lets in the apparatus to be tuned in line with the viscosity vary, making them flexible. Then again, they’re restricted to non-particulate samples and can’t be utilized in opaque samples for the reason that ball can’t be observed.

 Diagram of rolling ball viscometer. α indicates the angle of inclination, the arrow the direction of roll and dashed red lines the start and stop points for measurement.

Determine 4: Diagram of rolling ball viscometer. α signifies the attitude of inclination.

–          Rotational viscometers

Rotational viscometers function below the important of a rotational shifting section, pushed through a motor, involved with the check fluid. The torque at the rotating shaft is then used to decide the resistance to float of the fluid and calculate the dynamic viscosity. As a result of those tools are operated through a motor, they may be able to serve as below other shear charges. This selection permits them to function under and above the variety of gravity-based apparatus, thus enabling the dimension of a much broader vary of samples.1 Moreover, they permit viscosity measurements to be made for a pattern below other shear charges, thus facilitating the manufacturing of g viscosity curves, which might be elementary for non-Newtonian fluids.

The commonest variation of this sort of apparatus is known as the Brookfield viscometer that operates below the Searle idea9 (Determine 5). The motor drives a spindle within the mounted cup containing the check fluid. The rotational pace of the spindle reasons drag and as a result a definite motor torque. The torque wanted to triumph over the viscous forces of the examined fluid is subsequently a measure for its viscosity. The program can be utilized for each Newtonian and non-Newtonian meals and it’s the commonest form of viscometer this is utilized in high quality keep an eye on due its versatility. The apparatus operates at other rotational speeds and can be utilized with other spindles that experience other geometries. Those vary from discs, cylinders, cylinder-cones with other diameters and particular shapes together with various kinds of paddles and vanes, permitting the consumer to select other prerequisites for various pattern sorts, reminiscent of low viscosity, excessive viscosity, particulate and gel-like fluids.

Any other explicit geometry of rotational viscometers are the double-gap methods, which might be specifically devised for measuring low-viscosity fluids. The cup is a double concentric cylinder, reminiscent of an elongated ring, and the spindle is formed as an inverse cup that turns within the ring-shaped hole of the cup. This configuration maximizes the outside house involved with the fluid, thus, it is in a position to hit upon low torque values as generally generated through low-viscosity samples.

Diagram of the Brookfield viscometer (far left) and different spindle geometries, from left to right, disc, cylinder-cone, paddle and vane geometries.

Determine 5: Diagram of the Brookfield viscometer (a ways left) and other spindle geometries, from left to proper, disc, cylinder-cone, paddle and vane geometries.

A an identical idea can be utilized in parallel plate and cone plate geometries. In some of these geometries, a plate or a cone rotates over a pattern put on a set plate (Determine 6). Those methods function with slender gaps between the shifting geometry and the mounted plate, subsequently just a small quantity of pattern is needed. Then again, the small hole limits the solution to non-particulate samples and through being open at the aspect, the pattern can get away below upper rotational speeds, through the motion of turbulent float and centrifugal forces. Alternatively, the wedge-shaped hole led to through the cone leads to a continuing shear charge being carried out over all the hole, yielding benefits for the dimension of absolute viscosity values.2

Diagram of parallel plate (left) and cone plate (right) geometries.

Determine 6: Diagram of parallel plate (left) and cone plate (proper) geometries.

–          Vibrational viscometers and oscillation viscometers

Vibrational viscometers function through measuring the damping of an oscillating resonator immersed within the check fluid, which vibrates like a tuning fork (Determine 7A). An electromagnetic pressure controls the vibration of the sensor plates, and the power concerned within the resonance can also be decided through measuring the power used to take care of the vibration at a continuing amplitude, because the damping imposed through the fluid is immediately proportional to its viscosity. Any other choice is to decide the decay time of the oscillation as soon as the facility enter is reduce, because the decay could also be immediately proportional to the fluid’s viscosity.10

Oscillation viscometers use a unmarried probe (a sphere, rod or plate) vibrating involved with the check fluid (Determine 7B). A vibrating floor involved with the check fluid imposes shear pressure because of the outside motion, so the viscosity can also be decided through measuring the facility vital to take care of a continuing amplitude of oscillation.10

Vibrational and oscillation viscometers yield benefits reminiscent of excessive sensitivity on a variety of viscosities (from low viscosity liquids to semisolid or clogging fluids), haven’t any shifting portions and are smooth to take care of. This feature makes these kinds of apparatus the gold usual for in-line measurements in pipelines and tanks.

Diagram of vibrational (A) and oscillating (B) viscometers, with arrows indicating the direction of movement within the sample.

Determine 7: Diagram of vibrational (A) and oscillating (B) viscometers.

        Different form of tools

There also are imitative viscometers that depend on empirical rules to imitate the float of non-Newtonian fluid meals below operational prerequisites. This straightforward equipment generally supplies a one-point dimension. Even supposing they have got restricted sensitivity and running vary, they may be able to be helpful in high quality keep an eye on and tough measurements. A just right instance of this magnificence of kit is the Bostwick Consistometer (Determine 8), comprising a pattern compartment (a) with a gate operated through a spring cause (b). As soon as the gate is opened, the check fluid flows over a ramp (c) sitting at a particular perspective. After a longtime time, the duration travelled through the flowing pattern is recorded, and is proportional to the product’s viscosity. This apparatus is straightforward to function, tough and offers speedy and constant choice, being specifically fitted to sauces, pastes, jams and all more or less extremely viscous and particulate-containing meals.

Diagram of the Bostwick Consistometer, showing the sample compartment (a) with a gate operated by a spring trigger (b) and the ramp down which the sample flows (c) sitting at a specific angle.

Determine 8: Diagram of the Bostwick Consistometer.

As prior to now mentioned, viscometers are most often easy-to-operate tools, supply speedy effects and may also be utilized in online measurements. Then again, so as to measure viscosity as it should be, a sequence of things should be thought to be, specifically:

  • temperature diversifications
  • segment separation
  • non-uniform samples because of the presence of huge debris

Subsequently, in line with the specificities of the product being measured, probably the most suitable form of tool should be decided on.11

With regards to procedure keep an eye on tools, they’re put in throughout the processing plant set up (e.g., tanks or pipes) so as to download real-time knowledge of the method. Tube sort, vibrational or oscillation sort viscometers are ideally used for these kinds of packages.12 Referring to high quality keep an eye on measurements, the place samples are taken on a random foundation to validate the processing prerequisites and the standard requirements of a product, rotational, “U” tube viscometers or Bostwick Consistometers are continuously used. Those tools are the main selection in those packages as they’re flexible, can give measurements for various kinds of samples and processing prerequisites (e.g., extensive viscosity vary and operational temperature) and will temporarily give you the vital knowledge in commercial prerequisites. If wanted, they may be able to be wiped clean temporarily and tailored to different operational prerequisites, permitting the dimension of a number of samples with other specificities in a brief length. It’s this type of versatility and fast reaction that yields the best benefit of viscometers towards probably the most exact tools reminiscent of rheometers.13

Makes use of of viscometry within the meals and beverage {industry}

Many components might affect the standard and balance of meals, and viscosity is indisputably one of the crucial facets receiving extra consideration all over the producing procedure. Referring to meals manufacturing, viscosity is a key parameter in optimizing float prerequisites, dimensioning pumps, pipelines, power intake, lowering waste and within the keep an eye on of the general product’s high quality.1,14

Viscosity could also be very related within the system phases of meals merchandise. Let’s take the instance of bakery merchandise, during which quite a lot of levels (i.e., flour, water, fats, air) are blended to a solid dispersion. So as to take care of that dispersion, keep away from segment separation and retain air all over blending and baking, the gadget should dangle enough viscosity. The similar idea applies for the preparation of foams, emulsions and colloidal suspensions reminiscent of in sauces, soups, custards and so forth.

High quality keep an eye on is every other house the place viscosity determinations are continuously carried out and are elementary for the meals {industry}. They are able to be used to keep an eye on the standard of the substances, reminiscent of syrups, oils and liquid egg amongst others. This now not simplest validates their suitability for use at the processes, but in addition lets in analysts to expect deviations and carry out corrections at the formulations. In regards to the ultimate product keep an eye on, viscosity determinations are usual how to validate the product’s high quality and balance and make sure they meet technical specs.

However the significance of viscosity determinations within the meals {industry} reaches a ways past the classical manufacturing fashions and it’s also important in aiding the continuing meals revolution. Fueled through environmental, moral and societal adjustments, manufacturing and intake patterns are being redefined. New meals, reminiscent of meat analogues, goal to cut back or shift protein intake from animal-based to plant-based assets. The advance of meat possible choices and meat analogues depends on cutting edge tactics reminiscent of 3-D printing or excessive moisture extrusion, the usage of protein-based substances in addition to gums and different polymers. The function of those processes is to create the proper texture and consistency to emulate the beef construction. Viscosity used to be discovered to be a key issue, defining the design of kit, processes and being a determinant issue within the ultimate homes of the evolved meals.15,16, 17

The design of recent meals additionally follows the fad of offering further protection and well being advantages. Meals merchandise evolved for explicit pathologies at the moment are a truth, and a few of the maximum commonplace circumstances are formulations concentrated on deglutition keep an eye on in child meals or dysphagia sufferers.18 It’s been reported {that a} rational design in line with the keep an eye on of viscosity at explicit shear charges lowered the chance of asphyxiation.19 Any other motion house is the connection between the stomach-emptying charge and satiety, digestion and glycemic index. If truth be told, it used to be established that the viscosity of meals performs a decisive function in gastric-emptying, and subsequently the design of tuned viscosity meals might deliver vital implications in public well being, probably serving to to keep an eye on diabetes and weight problems.20

Subsequently, it may be concluded that the choice of the viscosity in meals and drinks and their substances is an important in high quality and procedure keep an eye on, and in addition affects the intake, sensory enjoy, protection and well being of the shoppers. The tactics used to measure viscosity are continuously easy and fast, however cautious variety a few of the quite a lot of check apparatus and stipulations is prime to acquire high quality measurements. The choice might be decided through the kind of meals product and alertness, and is influenced through the temperature, pattern homogeneity, segment adjustments and form of float.


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