The importance of viscosity measurement in food production and processing

Knowing the viscosity plays an important part in any industrial sector where liquid media are involved.

For instance, viscosity plays a role in nearly all production stages in the food sector. For example, lots of liquid media must be carefully pumped through pipelines. The viscosities in this sector range from aquaeous to pasty.

In industrial food processing, different types of sugar are used frequently, such as glucose syrup to sweeten food and beverages. Many types of syrup are obtained from enzymatic degradation of starch and are important products for the starch industry. Since syrups are sticky, they are often used as binders in the production of food, e. g. of chocolate cereal mixes or sauces. The viscosity and the flow properties highly depend on the adhesive properties of the starch contained in the food. Starch has varying characteristics, depending on the temperature and the environment. For example, when the temperature increases, it has a solidifying effect. However, when boiled, it has a liquefying effect. When it cools down again, it has a solidifying effect again. These conditions are characterised by viscosity. Even for soups, the right consistency is achieved by adding thickeners. When determining the flow properties of sauces, dips, mayonnaises and liquid additives for quality control, the temperature-dependent viscosity plays an important role.

As viscosity changes the flow properties of a liquid food and influences the appearance and the consistency of a product, this measuring variable is important in most production stages.

In the quality control of incoming liquid raw materials, viscosity is also an important control variable when it comes to differentiating between different qualities of raw materials and eliminating problems when further processing them. Depending on the application, random measurements in the laboratory are sufficient for the production of raw materials but in some cases, it is necessary to measure selectively on site or continuously (inline measurement). In many cases, it is necessary to save and transfer measured values. Therefore, some companies offer viscometers with an RS-232 interface and PC software. PCE Instruments, for example, offer a model which is suitable for the food, chemical and the cosmetics industry and measures viscosities between 3 and 13,000,000 mPas, at an accuracy of ±1 %.

As you can see, a quick and easy determination of viscosities is very important in quality and process control.

How can you measure viscosity?

Viscometers are devices which measure the toughness (viscosity) of a liquid and define it as a physical measuring variable to make it comparable. Viscometers vary in the measuring principle and in the type of viscosity measured (dynamic or kinematic viscosity).

Roughly, there are the following types of viscometers: capillary viscometers, rotational viscometers, falling body viscometer, process viscometer, viscosity flow cup.

These different types of viscometers are used depending on the application, quantity and measurement range of a sample.

For most viscosity measurements in quality control, samples are taken on a random basis and the dynamic viscosity is then measured precisely and quickly by means of a rotational viscometer. The rotational viscometer does this by measuring the mechanical resistance of a liquid which acts against the rotational movement of a spindle (as a rotational solid). The viscosity value arises from the resulting torque as referred to the spindle geometry. A rotational viscometer also measures the temperature of the sample liquid and shows it in an LC display along with some more parameters such as the spindle speed, the chosen spindle or the set measurement range. The rotational viscometers PCE-RVI 1, PCE-RVI 2 and PCE-RVI 3 are small but robust devices which can be used for almost any liquid medium. The stainless steel sensor is immersed into the liquid to be measured and the measurement result is immediately available. The probe tip must be completely covered in liquid. The size of the container and the volume of the liquid do not matter.

PCE Instruments offers different types of viscometers which are suitable for various applications.