Process Engineering Consultancy
Extrusion Process Modelling
Extrusion process modelling aims to quantitatively understand the impact of feed formulation, equipment setup, and process operating conditions on the physical quality of feed pellets. In feed pellet manufacturing, the nutritional quality of feed pellets is determined by the nutrient profile of the feed formulation, while the physical quality is influenced by formulation, equipment, and process conditions. The purpose of modelling is to establish correlations between these factors and key physical quality parameters of feed pellets, such as durability, bulk density, hardness, oil absorption, and water stability.
When formulating feeds, the physical and processing characteristics of ingredients are just as important as their nutritional contents. Some ingredients primarily contribute nutritional value, such as fishmeal, while others function as binders within the ingredient mixture, such as wheat flour, wheat gluten, and corn gluten. A fundamental requirement in feed manufacturing is that the ingredient mixture must possess sufficient binding capacity to form stable pellets.
An extruder is a fundamental tool for processing formulated ingredient mixtures. The geometric parameters and configurations of the extruder determine the shear energy applied to the mix, the residence time of the material during processing, etc. Extruder configurations are set before production and cannot be altered during operation, except through the installation of additional device such as a shear lock.
Extrusion process variables control the degree of processing and must be adjusted in response to feed pellet quality measurements. However, in many industrial settings, these adjustments still rely on operator expertise and trial-and-error methods. The goal of extrusion process modelling is to translate these skills into scientific knowledge by developing quantitative correlations between feed pellet quality parameters and process variables.
Model Development
One approach to establishing correlations between pellet quality parameters and process variables is the application of a viscous property model within the extrusion system. The correlation can be expressed as below Equation (1):
where Yprop is a feed pellet quality parameter (hardness, oil adsorption, durability, bulk density, etc.), k1, ni, α, ΔE and k2 are the experimental data determined parameters and can be obtained from experimental data regression, Ns is the screw speed, rpm or 1/s, R is the constant, 8.314 J/mol×K, T is the absolute die temperature, K, M is the moisture content, g/g, xi is the composition of ingredient i, g/g.
This model enables the prediction of feed pellet quality parameters based on ingredient composition and extrusion variables. Since different extrusion systems and feed formulations result in varying model coefficients, experimental data fitting is required to determine specific model parameters. Further details can be found in the works of Cheng et al. (2024, 2025).
References
Cheng H, Samuelsen T.A., Sørensen M, et al. (2024). Prediction of extruded aquafeed physical quality parameters through a dough viscosity model. J Food Process Eng, 47. https://doi.org/10.1111/jfpe.14604
Cheng H, Thorsteinsdottir A, Dalsgaard T.K., et al. (2025). Evaluation of the physical and chemical quality of Atlantic salmon feed with inclusion of full-fat black soldier fly or mealworm meal: Extrusion trials and modelling. Anim Feed Sci Technol, 320:116201. https://doi.org/10.1016/j.anifeedsci.2024.116201
Examples of the modelling results
Figure 1A-E. Feed pellet property values obtained from experimental data and those determined using Equation (1) for black solider fly larvae (BSFL) and mealworm (MW) addition recipes
