February 8, 2023

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The Viscometer and Its Function within the Meals and Beverage Business

16 min read

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

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

When a drive or tension is utilized to a fluid, it flows, leading to inner friction that resists the glide. Due to this fact, viscosity is outlined as the inner friction of a fluid, or in different phrases, its capability to withstand glide.

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

The shear tension is the drive in step with space had to transfer a laminar layer of fluid, while the shear fee 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 fee (e.g., water). Then again, the vast majority of fluids don’t behave this fashion, being referred to as non-Newtonian, and other issues are required to measure their viscosity. For a better figuring out of those phenomena and its implications, further studying is really helpful.1

In sensible phrases, a fluid with the next viscosity would glide extra slowly and seem thicker than a fluid with decrease viscosity (Determine 1). This assets is very dependent at the intrinsic traits of a subject material corresponding to molecular composition, solute focus, structural group and density. Moreover, viscosity must now not be perceived as an absolute price, however relatively a serve as of exterior components corresponding to temperature, shear and force, all of which impact viscosity, and thus, the technological and organoleptic homes of a meals product.

Determine 1: Float 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 All these tools simplest measure viscosity below one glide situation, opposite to different categories of tools which might be in a position to resolve viscosity below various glide stipulations, referred to as rheometers. Even if viscometers are regarded as much less flexible and actual, they’re less expensive, transportable, more uncomplicated to function and supply quicker determinations, making them first selection in manufacturing and high quality keep watch over packages.5

How does a viscometer paintings?

Viscosity determinations will also be carried out according to various 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 glide 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 accordance with the relative movement and geometry of the apparatus, various kinds of viscometer, in addition to their accuracies and goal packages will also be outlined. Taking into account the other viscometry methodologies, there are two distinct tactics to specific viscosity, absolute viscosity or kinematic viscosity. Absolutely the or dynamic viscosity is decided via looking at the fluid’s resistance to glide below a managed exterior drive, whilst the kinematic viscosity is decided via looking at the fluid’s glide below the motion of gravity.1 Those two tactics of expressing viscosity will also be interconverted via bearing in mind the fluid’s density, multiplying the kinematic viscosity via the density of the fluid to procure absolutely the viscosity, or dividing absolutely the viscosity via the density to procure the kinematic viscosity.

Not unusual varieties of viscometers

–          Capillary viscometer and glide cups (orifice viscometers)

The operating concept of those tools is according to the resolution of the time wanted for the standard quantity of fluid to cross via a capillary. The straightforward design and simple operation cause them to excellent possible choices for regimen measurements and high quality keep watch over. But, they’re restricted to low viscosity liquids with out forged debris in suspension, which restricts their usage to drinks and liquid components. Probably the most not unusual configurations is the “U” form capillary of the Ostwald viscometer offered 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 cross during the marks is recorded and multiplied via an tool consistent to determine the kinematic viscosity of the fluid.2 The time it takes for the fluid to cross during the capillary tube is at once proportional to the dynamic viscosity and inversely proportional to the density of the fluid. Any other easy configuration of a capillary viscometer is the glide cup or orifice sort viscometer (Determine 2B). This apparatus include a reservoir and orifice or capillary, and works via figuring out the time it takes for the fluid to cross during the orifice.7 Those tools are affordable, smooth to function and flexible, alternatively they don’t seem to be correct as they don’t make sure 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 glide cup (B) and tube viscometer (C).

Pressurized variations of the capillary and glide cup viscometers can be utilized to be able to care for a relentless force right through the dimension and to function below excessive pressures, enabling their usage for extremely viscous fluids. In such instances, the fluid is moved via fuel force or via a piston that may be prompted via a weight or a riding motor.

In the similar class of capillary viscometers, tube viscometers (Determine 2C) use a horizontal tube fed via a pressurized tank to resolve viscosity.2 In those tools, the force is decided at other positions alongside the tube, and the force drop at a particular glide fee is used to calculate the resistance to glide, and thus the viscosity. Tube viscometers are particularly suited to online determinations and frequently 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 take a look at fluid, the piston drops below 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 will also be decided. The power to keep watch over the shear charges, via converting the piston’s mass, makes this apparatus appropriate to signify fluids eager about excessive shear fee operations. Those tools also are smooth to function and care for, providing a protracted product existence. The primary downside is that efficiency for non-homogeneous samples, corresponding 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 would possibly range from a vertical configuration (between 80° and 90°), permitting a unfastened 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 at once 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 suited to measuring Newtonian fluids, are smooth to function and will also 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. 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 essential of a rotational transferring phase, pushed via a motor, in touch with the take a look at fluid. The torque at the rotating shaft is then used to resolve the resistance to glide of the fluid and calculate the dynamic viscosity. As a result of those tools are operated via a motor, they may be able to serve as below other shear charges. This option lets them function underneath and above the variability of gravity-based apparatus, thus enabling the dimension of a wider vary of samples.1 Moreover, they enable viscosity measurements to be made for a pattern below other shear charges, thus facilitating the manufacturing of g viscosity curves, which can 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 concept9 (Determine 5). The motor drives a spindle within the fastened cup containing the take a look at fluid. The rotational pace of the spindle reasons drag and because of this a definite motor torque. The torque wanted to triumph over 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 various kinds of paddles and vanes, permitting the person to make a choice other stipulations for various pattern varieties, corresponding to low viscosity, excessive viscosity, particulate and gel-like fluids.

Any other particular geometry of rotational viscometers are the double-gap methods, which can be specifically devised for measuring low-viscosity fluids. The cup is a double concentric cylinder, corresponding 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 space in touch with the fluid, thus, it is in a position to locate low torque values as in most cases generated via 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 (some distance left) and other spindle geometries, from left to proper, disc, cylinder-cone, paddle and vane geometries.

A an identical concept can be utilized in parallel plate and cone plate geometries. In most 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 transferring geometry and the fastened plate, due to this fact just a small quantity of pattern is needed. Then again, the small hole limits the approach to non-particulate samples and via being open at the facet, the pattern can break out below upper rotational speeds, via the motion of turbulent glide and centrifugal forces. However, the wedge-shaped hole led to via the cone ends up in a relentless shear fee being utilized over all of 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 via measuring the damping of an oscillating resonator immersed within the take a look at 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 will also be decided via measuring the power used to care for the vibration at a relentless amplitude, because the damping imposed via the fluid is at once proportional to its viscosity. Any other selection is to resolve the decay time of the oscillation as soon as the facility enter is lower, because the decay may be at once proportional to the fluid’s viscosity.10

Oscillation viscometers use a unmarried probe (a sphere, rod or plate) vibrating in touch with the take a look at fluid (Determine 7B). A vibrating floor in touch with the take a look at fluid imposes shear tension because of the outside motion, so the viscosity will also be decided via measuring the facility vital to care for a relentless amplitude of oscillation.10

Vibrational and oscillation viscometers yield benefits corresponding to excessive sensitivity on a variety of viscosities (from low viscosity liquids to semisolid or clogging fluids), haven’t any transferring portions and are smooth to care for. This feature makes some of these apparatus the gold same old 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 ideas to imitate the glide of non-Newtonian fluid meals below operational stipulations. This easy equipment in most cases supplies a one-point dimension. Even if they’ve restricted sensitivity and working vary, they may be able to be helpful in high quality keep watch over and tough measurements. A excellent instance of this magnificence of apparatus is the Bostwick Consistometer (Determine 8), comprising a pattern compartment (a) with a gate operated via a spring cause (b). As soon as the gate is opened, the take a look at fluid flows over a ramp (c) sitting at a particular perspective. After a longtime time, the duration travelled via the flowing pattern is recorded, and is proportional to the product’s viscosity. This apparatus is simple to function, powerful and gives 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 also be utilized in online measurements. Then again, to be able to measure viscosity as it should be, a chain of things will have to be regarded as, specifically:

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

Due to this fact, consistent with the specificities of the product being measured, essentially the most suitable form of tool will have to be decided on.11

With regards to procedure keep watch over tools, they’re put in throughout the processing plant set up (e.g., tanks or pipes) to be able to download real-time information of the method. Tube sort, vibrational or oscillation sort viscometers are ideally used for some of these packages.12 Relating 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 frequently used. Those tools are the principle selection in those packages as they’re flexible, can give measurements for various kinds of samples and processing stipulations (e.g., broad viscosity vary and operational temperature) and will briefly give you the vital information in commercial stipulations. If wanted, they may be able to be wiped clean briefly and tailored to different operational stipulations, permitting the dimension 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 towards essentially the most actual tools corresponding to rheometers.13

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

Many components would possibly affect the standard and balance of meals, and viscosity is no doubt probably the most facets receiving extra consideration right through the producing procedure. Relating to meals manufacturing, viscosity is a key parameter in optimizing glide stipulations, dimensioning pumps, pipelines, power intake, decreasing waste and within the keep watch over of the overall product’s high quality.1,14

Viscosity may be very related within the system phases of meals merchandise. Let’s take the instance of bakery merchandise, wherein various stages (i.e., flour, water, fats, air) are blended to a solid dispersion. So as to care for that dispersion, steer clear of segment separation and retain air right through blending and baking, the device will have to cling enough viscosity. The similar concept applies for the preparation of foams, emulsions and colloidal suspensions corresponding to in sauces, soups, custards and so forth.

High quality keep watch over is every other space the place viscosity determinations are frequently carried out and are elementary for the meals {industry}. They are able to be used to keep watch over the standard of the components, corresponding to syrups, oils and liquid egg amongst others. This now not simplest validates their suitability for use at the processes, but additionally permits analysts to expect deviations and carry out corrections at the formulations. In regards to the ultimate product keep watch over, viscosity determinations are same old 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 some distance past the classical manufacturing fashions and it’s also essential in helping the continuing meals revolution. Fueled via environmental, moral and societal adjustments, manufacturing and intake patterns are being redefined. New meals, corresponding to meat analogues, goal to scale back or shift protein intake from animal-based to plant-based assets. The improvement of meat possible choices and meat analogues relies on cutting edge tactics corresponding to 3-D printing or excessive moisture extrusion, the usage of protein-based components in addition to gums and different polymers. The objective of those processes is to create the precise texture and consistency to emulate the beef construction. Viscosity was once 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 fad of offering further protection and well being advantages. Meals merchandise advanced for particular pathologies are actually a truth, and a number of the maximum not unusual instances are formulations focused on deglutition keep watch over in child meals or dysphagia sufferers.18 It’s been reported {that a} rational design according to the keep watch over of viscosity at particular shear charges decreased the danger of asphyxiation.19 Any other motion space is the connection between the stomach-emptying fee and satiety, digestion and glycemic index. In reality, it was once established that the viscosity of meals performs a decisive position in gastric-emptying, and due to this fact the design of tuned viscosity meals would possibly carry necessary implications in public well being, doubtlessly serving to to keep watch over diabetes and weight problems.20

Due to this fact, it may be concluded that the resolution of the viscosity in meals and drinks and their components is an important 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 frequently easy and fast, however cautious variety a number of the more than a few take a look at apparatus and prerequisites is prime to procure high quality measurements. The choice can be decided via the kind of meals product and alertness, and is influenced via the temperature, pattern homogeneity, segment adjustments and form of glide.


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