Rheological Modeling of Cheese Extrusion

Abstract

Understanding the physical properties and flow behaviour of foods is essential for
designing reliable processing equipment. In this thesis, the rheological properties and
flow behaviour of Pasta Filata cheese are investigated to improve the understanding of
the flow-distribution inside a Tetra Pak Cheese Extruder. Uneven flow-rates have been
observed during production, which lead to inconsistent dimensions of the final product.
These variations are believed to be a consequence of non-Newtonian properties of the
cheese. This thesis presents a theoretical and numerical investigation of the flow
behaviour in a cheese extruder.
The literature study showed that Pasta Filata is a shear- and temperature-thinning
viscoelastic material. The viscosity was considered to be best modeled by Power-Law
or Herschel-Bulkley models. Research also showed that viscoelastic flows can exhibit
elastic instabilities even at low Reynolds numbers, potentially explaining transient
behaviour of the flow-rates.
Viscosity models, Power-law and Herschel-Bulkley, were fitted to data from the experimental study conducted by Muliawan and Hatzikiriakos [1] (2007). This was implemented in the Computational Fluid Dynamics (CFD) simulations in the software
StarCCM+ to simulate the flow in the cheese extruder. Several thermal cases were
simulated to reflect the combination of heated and uninsulated regions in the extruder.
The simulations showed that the flow distribution was strongly affected by the temperature. Cases with lower inlet temperature compared to the heating jackets reproduced
the steady-state phenomena of uneven flow-rates between the pipes observed during
production.
No transient behaviour of the flow could be captured by the simulations which supports
the theory that these possible fluctuations are due to elastic properties, which were
not included in the simulated rheological model.
This thesis concludes that the flow-distribution of Pasta Filata in an extruder is
strongly dependent on temperature. Improving thermal insulation in critical regions
of the process could reduce the uneven flow

Popular Abstract

String cheese is a popular mozzarella type snack usually found in lunchboxes across USA, Canada and Australia. It is still quite rare in Europe but global demand is growing. The company Tetra Pak, which supplies food processing equipment, provides a production line for making string cheese on an industrial scale.

During production, the cheese is pushed through a machine called an extruder which divides the flow into twelve small outlets that form the individual cheese sticks. In this step the company has encountered problems with the machine having an uneven flow between the twelve outlet pipes which leads to inconsistent lengths of the final product. The aim of my master thesis was to understand why the uneven flow occurs.

Melted cheese does not behave like simple liquids such as water. Its flow behaviour is strongly dependent on temperature and movement. When the cheese becomes warmer, it becomes softer and flows more easily. This is common for many liquid foods.

Some studies have found that melted cheese can show unstable flow behaviour where the flow can start to fluctuate or change direction unpredictably. This can occur in fluids with long molecules that can store and release energy which causes fluctuations in the flow. Similar effects have been seen in liquids such as melted plastics and blood.

The flow in the extruder was simulated using Computational Fluid Dynamics (CFD). A model describing the flow behaviour of the cheese at different temperatures was developed using data from an experimental study.

The cheese extruder has heated and uninsulated regions. Various scenarios were simulated to study how these thermal variations affect the flow distribution out from the twelve pipes.

The simulations showed that the outlet velocities were highly sensitive to temperature. If the cheese near the wall became slightly warmer than in the center, it flowed more easily, leading to higher velocities in the outer pipes. This flow phenomenon matched what was observed during production. The most interesting part of the study was that changing the inlet temperature by just one degree was enough to alter the flow distribution.

• author: Lindbäck, Tyra
• supervisor: Johan Revstedt; Dragana Arlov; Yuxiao Zhao
• organization: Department of Energy Sciences
• course: MVKM01 20252
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Rheology, CFD, Star-CCM+, Viscosity, Elasticity, Cheese, Extrusion, Shear-thinning, Elastic Instabilities, Non-Newtonian, Power law, Herschel-Bulkley, Viscoplastic, Viscoelastic
• report number: ISRN LUTMDN/TMHP-26/5671-SE
• ISSN: 0282-1990
• language: English
• id: 9223657
• date added to LUP: 2026-04-22 10:48:29
• date last changed: 2026-04-22 10:48:29