From Relative to Absolute – Predicting Viscosity in Food Processing and Packaging

Abstract

Viscosity and rheological behaviour are key parameters in anything from the eating experience and mouthfeel of a product to the design choices of pumps, pipes, and down to the filling of packages in packaging and processing equipment. Many companies in the food industry use relative methods of measuring viscosity for quality assurance, as they are usually simple and inexpensive. However, these relative values cannot be directly used by companies to design packaging and processing equipment. Therefore, to ease the communication between customers and producers of packaging and processing equipment, this study aims to see how and to what extent absolute viscosity and rheological behaviour can be predicted from relative measurement methods, the Bostwick consistometer and Brookfield viscometer. Additionally, the study investigated whether it was possible to characterise foods with different rheological properties, such as Newtonian, shear-thinning, and thixotropic.

For the Bostwick, this was done by using a gravity-based method and measuring the time it took to reach different distances. The data was used to predict n and K in the power law fluid model, and these, together with the theoretical pressure drop, were compared to the obtained values from the rheometer. Similarly, the so-called “Mitschka method” was applied to the torque data from the Brookfield for the foods measured at different tip speeds and measuring times.

It was found that the Bostwick combined with the gravity-based model could not reliably predict n, K, or the relative error in pressure drop compared to the rheometer for any of the food categories. The Brookfield, together with the Mitschka method, yielded mixed results. Most products’ n and K values were poorly predicted. However, for a protein yoghurt, the differences in n and K were -5.36 to 7.08 % and 7.84 to 19.3 % respectively, but significantly different to the rheometer’s values. The n values could also be well predicted for the Newtonian products. The relative error in pressure drop was also poorly predicted without a clear trend, except for the protein yoghurt with a measuring time of 120 s, yielding -8.07 and -2.18 % for the turbulent and laminar cases, respectively.

In conclusion, as of now, neither of the relative methods can be used to accurately predict the viscosity or rheological parameters. However, there is potential to further refine the Mitschka method for predictions of rheological characteristics of foods, at least for an initial assessment.

Popular Abstract

Have you ever wondered why yoghurt pours the way it does or why the ketchup effect exists? It all has to do with viscosity and rheology, properties that affect your eating experience and how food companies design their production processes.

Viscosity and rheology affect the design decisions of pipes, pumping systems, and all the way down to how the product can be filled in the package you open each day. Rheology is the science of how products flow and deform when you apply forces to them, like stirring, chewing, and pouring, and is therefore vital for both companies and the consumer experience.

Today, many companies use simple relative methods to check the viscosity of their products, like how thick or runny it is, to ensure the quality. However, companies producing processing and packaging machines cannot directly use these measurements and instead use their own more precise methods to get absolute measurements. This can lead to miscommunication between customers and producers of food packaging and processing equipment. How viscous a product is can be very difficult to describe when one basically speaks a different language and uses different units to measure it, like comparing Chinese and English! That is why it would be greatly beneficial for both parties, improving communication and economic efficiency, if the customers’ measurements could be used for at least an initial assessment of their products.

This study explored whether two common relative tools, the so-called Bostwick consistometer and Brookfield viscometer, could be compared to a more advanced tool called a rotational rheometer, which gives absolute measurements. Using models from literature and various types of experiments, the study looked at how well the simpler tools could estimate key flow properties of different foods, like how easily they move in a pipe. The most important parameters that were compared are the n and K values from the commonly used power law model, as well as the pressure drop.

As expected, the results showed that it is difficult to translate simpler relative measurements to more advanced absolute ones. The Bostwick consistometer did not give reliable results, and the equations from the original study need to be revisited. The Brookfield viscometer, paired with an old method from a Czech book from 1982 (called the Mitschka method), showed some promising results. The golden star of the study is a protein yoghurt that appears to be well-characterised, showing potential for refining this old analytical method. Also, newer studies have found success with this old method. Hopefully, or rather perhaps, with further refinement of the old-school Czech method, measurements from the Brookfield viscometer can be used for at least a first assessment of foods in the near future.

• author: Ekelund, Hanna
• supervisor: Andreas Håkansson; Dragana Arlov; Helena Andrén Wijkander; Hannah Viklund
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLTM06 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Viscosity measurement, rheological properties, power law fluid model, Bostwick Consistometer, Brookfield Viscometer, Mitschka Method, Food engineering nutrition and food
• language: English
• id: 9196004
• date added to LUP: 2025-06-13 11:53:35
• date last changed: 2025-06-13 11:53:35