February 8, 2023

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The Viscometer and Its Position within the Meals and Beverage Trade

16 min read

Viscosity performs a decisive function in meals science and the meals {industry}. This parameter is a very powerful in high quality keep watch over and procedure design, affecting operations similar to stirring and homogenization, pumping and packaging amongst others.1 It is usually a basic issue affecting meals intake, being function of meals texture,2 taking part in crucial function in taste belief or even having well being and protection implications in processes similar to deglutition and digestion.3

On this article, we will be able to believe what viscosity is, how it’s measured and the programs of viscometry within the meals and beverage {industry}.

When a power or pressure is implemented to a fluid, it flows, leading to inside friction that resists the waft. Subsequently, viscosity is outlined as the inner friction of a fluid, or in different phrases, its capability to withstand waft.

Making an allowance for a fluid as a lot of laminar layers, the components describing viscosity is easy, being represented in centipois (cP) or Pascal seconds (Pa s):

The shear pressure is the power in line with house had to transfer a laminar layer of fluid, while the shear charge is the relation of velocity between two laminar layers of fluid. That is best legitimate for Newtonian fluids, the place at a undeniable temperature, the viscosity would stay consistent as a serve as of adjustments in shear charge (e.g., water). On the other hand, the vast majority of fluids don’t behave this manner, being known as non-Newtonian, and other concerns are required to measure their viscosity. For a closer working out of those phenomena and its implications, further studying is really useful.1


In sensible phrases, a fluid with a better viscosity would waft extra slowly and seem thicker than a fluid with decrease viscosity (Determine 1). This assets is extremely dependent at the intrinsic traits of a subject material similar to molecular composition, solute focus, structural group and density. Moreover, viscosity must now not be perceived as an absolute price, however slightly a serve as of exterior elements similar to temperature, shear and drive, all of which have an effect on viscosity, and thus, the technological and organoleptic homes of a meals product.


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 device used to measure the viscosity of a fluid.4 A lot of these tools best measure viscosity beneath one waft situation, opposite to different categories of tools which are ready to resolve viscosity beneath various waft stipulations, known as rheometers. Even though viscometers are thought to be much less flexible and actual, they’re inexpensive, moveable, more uncomplicated to function and supply sooner determinations, making them first selection in manufacturing and high quality keep watch over programs.5

How does a viscometer paintings?

Viscosity determinations can also be carried out in line with 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 waft stipulations will have to 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, different types of viscometer, in addition to their accuracies and goal programs can also be outlined. Making an allowance for the other viscometry methodologies, there are two distinct techniques to specific viscosity, absolute viscosity or kinematic viscosity. Absolutely the or dynamic viscosity is decided by way of watching the fluid’s resistance to waft beneath a managed exterior power, whilst the kinematic viscosity is decided by way of watching the fluid’s waft beneath the motion of gravity.1 Those two techniques of expressing viscosity can also be interconverted by way of taking into consideration the fluid’s density, multiplying the kinematic viscosity by way of the density of the fluid to procure absolutely the viscosity, or dividing absolutely the viscosity by way of the density to procure the kinematic viscosity.

Not unusual forms of viscometers

–          Capillary viscometer and waft cups (orifice viscometers)

The operating idea of those tools is in line with the resolution of the time wanted for the standard quantity of fluid to move via a capillary. The easy design and easy operation lead them to just right choices for regimen measurements and high quality keep watch over. But, they’re restricted to low viscosity liquids with out cast debris in suspension, which restricts their usage to drinks and liquid elements. Probably the most not unusual configurations is the “U” form capillary of the Ostwald viscometer introduced in Determine 2A. Those tools are generally operated in a thermally-stabilized tub and after the higher bulb is stuffed with the fluid, the time wanted for the fluid to move during the marks is recorded and multiplied by way of an device consistent to determine the kinematic viscosity of the fluid.2 The time it takes for the fluid to move during the capillary tube is immediately proportional to the dynamic viscosity and inversely proportional to the density of the fluid. Every other easy configuration of a capillary viscometer is the waft cup or orifice kind viscometer (Determine 2B). This apparatus encompass a reservoir and orifice or capillary, and works by way of figuring out the time it takes for the fluid to move during the orifice.7 Those tools are affordable, clean to function and flexible, then again they aren’t correct as they don’t make sure that consistent drive 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 waft cup (B) and tube viscometer (C).


Pressurized variations of the capillary and waft cup viscometers can be utilized so as to care for a relentless drive all through the size and to function beneath excessive pressures, enabling their usage for extremely viscous fluids. In such circumstances, the fluid is moved by way of fuel drive or by way of a piston that may be prompted by way of a weight or a using motor.

In the similar class of capillary viscometers, tube viscometers (Determine 2C) use a horizontal tube fed by way of a pressurized tank to resolve viscosity.2 In those tools, the drive is decided at other positions alongside the tube, and the drive drop at a particular waft charge is used to calculate the resistance to waft, and thus the viscosity. Tube viscometers are particularly suited to online determinations and steadily 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 beneath the motion of gravity, displacing the fluid during the gaps between the piston and the cylinder (Determine 3), inflicting a shearing impact.8 By way of measuring the piston’s falling time, pattern viscosity can also be decided. The facility to keep watch over the shear charges, by way of converting the piston’s mass, makes this apparatus appropriate to represent fluids excited about excessive shear charge operations. Those tools also are clean to function and care for, providing a protracted product lifestyles. The principle downside is that efficiency for non-homogeneous samples, similar to particulate suspensions, is also 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 loose fall of the ball, thus being designated a falling ball viscometer, or prone (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 size are the fluid density, the ball density, the period and time of the ball motion and its terminal velocity. Those tools are smartly suited to measuring Newtonian fluids, are clean to function and will even be simply improvised in a laboratory. The adjustment of the attitude permits the apparatus to be tuned consistent with the viscosity vary, making them flexible. On the other hand, they’re restricted to non-particulate samples and can’t be utilized in opaque samples for the reason that ball can’t be noticed.

 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 beneath the fundamental of a rotational shifting section, pushed by way of a motor, involved with the check fluid. The torque at the rotating shaft is then used to resolve the resistance to waft of the fluid and calculate the dynamic viscosity. As a result of those tools are operated by way of a motor, they are able to serve as beneath other shear charges. This option lets them function beneath and above the variability of gravity-based apparatus, thus enabling the size of a wider vary of samples.1 Moreover, they enable viscosity measurements to be made for a pattern beneath other shear charges, thus facilitating the manufacturing of g viscosity curves, that are basic for non-Newtonian fluids.


The commonest variation of this sort of apparatus is known as the Brookfield viscometer that operates beneath the Searle idea9 (Determine 5). The motor drives a spindle within the mounted cup containing the check fluid. The rotational velocity of the spindle reasons drag and in consequence a undeniable motor torque. The torque wanted to conquer the viscous forces of the examined fluid is due to this fact a measure for its viscosity. The program can be utilized for each Newtonian and non-Newtonian meals and it’s the most typical form of viscometer this is utilized in high quality keep watch over 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 different types of paddles and vanes, permitting the consumer to select other stipulations for various pattern sorts, similar to low viscosity, excessive viscosity, particulate and gel-like fluids.


Every other particular geometry of rotational viscometers are the double-gap methods, that are specifically devised for measuring low-viscosity fluids. The cup is a double concentric cylinder, similar to 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 stumble on low torque values as generally generated by way of 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 these types of geometries, a plate or a cone rotates over a pattern put on a hard and fast plate (Determine 6). Those methods function with slender gaps between the shifting geometry and the mounted plate, due to this fact just a small quantity of pattern is needed. On the other hand, the small hole limits the strategy to non-particulate samples and by way of being open at the aspect, the pattern can get away beneath upper rotational speeds, by way of the motion of turbulent waft and centrifugal forces. Then again, the wedge-shaped hole brought about by way of the cone leads to a relentless shear charge being implemented over all of the hole, yielding benefits for the size 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 by way of measuring the damping of an oscillating resonator immersed within the check fluid, which vibrates like a tuning fork (Determine 7A). An electromagnetic force controls the vibration of the sensor plates, and the power concerned within the resonance can also be decided by way of measuring the power used to care for the vibration at a relentless amplitude, because the damping imposed by way of the fluid is immediately proportional to its viscosity. Every other choice is to resolve the decay time of the oscillation as soon as the ability enter is lower, 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 by way of measuring the ability essential to care for a relentless amplitude of oscillation.10


Vibrational and oscillation viscometers yield benefits similar to excessive sensitivity on quite a lot of viscosities (from low viscosity liquids to semisolid or clogging fluids), don’t have any shifting portions and are clean to care for. This function makes most of these 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 waft of non-Newtonian fluid meals beneath operational stipulations. This straightforward equipment generally supplies a one-point size. Even though they’ve restricted sensitivity and running vary, they are able to be helpful in high quality keep watch over and tough measurements. A just right instance of this magnificence of apparatus is the Bostwick Consistometer (Determine 8), comprising a pattern compartment (a) with a gate operated by way of 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 period travelled by way of 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 resolution, being in particular suited to sauces, pastes, jams and all roughly 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 in the past mentioned, viscometers are generally easy-to-operate tools, supply speedy effects and will even be utilized in online measurements. On the other hand, so as to measure viscosity accurately, a sequence of things will have to be thought to be, specifically:

  • temperature permutations
  • section separation
  • non-uniform samples because of the presence of huge debris


Subsequently, consistent with the specificities of the product being measured, probably the most suitable form of device will have to be decided on.11


Relating to procedure keep watch over 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 kind, vibrational or oscillation kind viscometers are ideally used for most of these programs.12 Referring to high quality keep watch over measurements, the place samples are taken on a random foundation to validate the processing stipulations and the standard requirements of a product, rotational, “U” tube viscometers or Bostwick Consistometers are steadily used. Those tools are the main selection in those programs as they’re flexible, may give measurements for different types of samples and processing stipulations (e.g., large viscosity vary and operational temperature) and will briefly give you the essential knowledge in commercial stipulations. If wanted, they are able to be wiped clean briefly and tailored to different operational stipulations, permitting the size of a number of samples with other specificities in a brief length. It’s this sort of versatility and fast reaction that yields the best good thing about viscometers in opposition to probably the most actual tools similar to rheometers.13

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


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


Viscosity could also be very related within the method levels of meals merchandise. Let’s take the instance of bakery merchandise, wherein a lot of levels (i.e., flour, water, fats, air) are blended to a strong dispersion. With a view to care for that dispersion, keep away from section separation and retain air all through blending and baking, the gadget will have to hang enough viscosity. The similar idea applies for the preparation of foams, emulsions and colloidal suspensions similar to in sauces, soups, custards and so forth.


High quality keep watch over is any other house the place viscosity determinations are steadily applied and are basic for the meals {industry}. They are able to be used to keep watch over the standard of the elements, similar to syrups, oils and liquid egg amongst others. This now not best validates their suitability for use at the processes, but additionally permits analysts to are expecting deviations and carry out corrections at the formulations. In regards to the ultimate product keep watch over, viscosity determinations are usual the best way 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 is usually essential in aiding the continued meals revolution. Fueled by way of environmental, moral and societal adjustments, manufacturing and intake patterns are being redefined. New meals, similar to meat analogues, intention to scale back or shift protein intake from animal-based to plant-based assets. The advance of meat choices and meat analogues depends on leading edge tactics similar to 3-D printing or excessive moisture extrusion, the usage of protein-based elements in addition to gums and different polymers. The purpose of those processes is to create the fitting texture and consistency to emulate the beef construction. Viscosity used to be discovered to be a key issue, defining the design of apparatus, processes and being a determinant issue within the ultimate homes of the advanced meals.15,16, 17


The design of latest meals additionally follows the fashion of offering further protection and well being advantages. Meals merchandise advanced for particular pathologies are actually a fact, and some of the maximum not unusual circumstances are formulations concentrated on deglutition keep watch over in child meals or dysphagia sufferers.18 It’s been reported {that a} rational design in line with the keep watch over of viscosity at particular shear charges lowered the danger of asphyxiation.19 Every other motion house is the connection between the stomach-emptying charge and satiety, digestion and glycemic index. Actually, it used to be established that the viscosity of meals performs a decisive function in gastric-emptying, and due to this fact the design of tuned viscosity meals might convey essential implications in public well being, doubtlessly serving to to keep watch over diabetes and weight problems.20


Subsequently, it may be concluded that the resolution of the viscosity in meals and drinks and their elements is a very powerful in high quality and procedure keep watch over, and in addition affects the intake, sensory enjoy, protection and well being of the patrons. The tactics used to measure viscosity are steadily easy and fast, however cautious variety some of the more than a few check apparatus and prerequisites is prime to procure high quality measurements. The choice might be decided by way of the kind of meals product and alertness, and is influenced by way of the temperature, pattern homogeneity, section adjustments and form of waft.


References:

1.          Steffe JF. Rheological Strategies in Meals Procedure Engineering. 2d ed. East Lansing, USA: Freeman Press; 1996. ISBN:0-9632036-1-4

2.          Bourne M. Meals Texture and Viscosity – Idea and Size. 2d ed. Elsevier Science & Era Books; 2002. ISBN:978-0-12-119062-0

3.          Clavé P, Shaker R. Dysphagia: present fact and scope of the issue. Nat Rev Gastroenterol Hepatol. 2015;12(5):259-270. doi:10.1038/nrgastro.2015.49

4.          Edwards RA. Viscosity. In: Edwards RA ed. Physics for O.N.C. Lessons. Elsevier; 1970:41-52. doi:10.1016/C2013-0-02235-9

5.          Mezger T. The Rheology Manual. third ed.. Vincentz Community; 2020. doi:10.1515/9783748603702

6.          Rao MA. Viscosity of meals: Size and alertness. In: Encyclopedia of Analytical Chemistry. John Wiley & Sons, Ltd; 2006. doi:10.1002/9780470027318.a1031

7.          Joyner HS. Viscosity measurements of fluid meals merchandise. In: Meals Research Laboratory Handbook. third ed. Springer; 2017:213-217. doi:10.1007/978-3-319-44127-6_26

8.          Gupta SV. Rotational and different forms of viscometers. In: Viscometry for Liquids. Springer, Cham; 2014:81-105. doi:10.1007/978-3-319-04858-1_4

9.          Thomson GP. George Frederick Charles Searle, 1864-1954. Biogr Mem Fellows R Soc. 1955;1:246-252. doi:10.1098/rsbm.1955.0018

10.        Stieger M. The rheology guide – For sers of rotational and oscillatory rheometers. Appl Rheol. 2002;12(5):232. doi:10.1515/arh-2002-0029

11.        Abbas KA, Abdulkarim SM, Saleh AM, Ebrahimian M. Suitability of viscosity size strategies for liquid meals selection and applicability in meals industry-A assessment. J Meals, Agric Environ. 2010;8(3):100-107. ISSN:1459-0255

12.        Johnson JF, Martin JR, Porter RS. Choice of viscosity of meals methods. In: Rha C ed. Idea, Choice and Regulate of Bodily Homes of Meals Fabrics. Dordrecht: Springer Netherlands; 1975:25-38. doi:10.1007/978-94-010-1731-2_4

13.        Rao MA. Rheology of Fluid, Semisolid, and Forged Meals. New York, NY: Springer US; 2014. doi:10.1007/978-1-4614-9230-6

14.        Mckenna BM, Lyng JG. Ideas of meals viscosity research. In: Kilcast D, ed. Instrumental Review of Meals Sensory High quality. Woodhead Publishing; 2013:129-162. doi:10.1533/9780857098856.1.129

15.        Guyony V, Fayolle F, Jury V. Prime moisture extrusion of vegetable proteins for making fibrous meat analogs: A assessment. Meals Rev Int.. 2022:1-26. doi:10.1080/87559129.2021.2023816

16.        Jiang H, Zheng L, Zou Y, Tong Z, Han S, Wang S. 3-D meals printing: major elements variety by way of taking into consideration rheological homes. Crit Rev Meals Sci Nutr. 2019;59(14):2335-2347. doi:10.1080/10408398.2018.1514363

17.        Dekkers BL, Growth RM, van der Goot AJ. Structuring processes for meat analogues. Developments Meals Sci Technol. 2018;81(Would possibly):25-36. doi:10.1016/j.tifs.2018.08.011

18.        Frazier J, Chestnut AH, Jackson A, Barbon CEA, Steele CM, Pickler L. Working out the viscosity of liquids utilized in toddler dysphagia control. Dysphagia. 2016;31(5):672-679. doi:10.1007/s00455-016-9726-6

19.        Sukkar SG, Maggi N, Travalca Cupillo B, Ruggiero C. Optimizing texture changed meals for oro-pharyngeal dysphagia: A troublesome however conceivable goal? Entrance Nutr. 2018;5. doi:10.3389/fnut.2018.00068

20.        Jin Y, Wilde PJ, Hou Y, Wang Y, Han J, Liu W. An evolving view on meals viscosity regulating gastric emptying. Crit Rev Meals Sci Nutr. 2022:1-17. doi:10.1080/10408398.2021.2024132

 

  

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