The Mechanics of Edible Soft Matter: Fluid/Solid Modeling

The structuring of food materials during processing relies on continuous and rapid transitions between fluid-like and solid-like states. These state transformations govern critical operations, including spray drying, baking, frying, extrusion, and 3D food printing. Developing predictive continuum models for these operations remains a major hurdle in modern food engineering.

This challenge stems from the need for a unified theoretical framework bridging fluid mechanics, large-deformation solid mechanics, non-linear rheology, and multiphysics transport phenomena. Soft matter mechanics has undergone significant conceptual advancements; modern large-deformation continuum frameworks for soft solids now share fundamental structural similarities with viscoelastic fluid models. By leveraging non-equilibrium thermodynamics, these formulations yield consistent descriptions integrating elasticity, viscosity, yield stress, plasticity, and structural evolution. This convergence offers a mathematically rigorous pathway toward dissolving the traditional boundary between fluid and solid mechanics within a single constitutive setting.

In solid mechanics, unified continuum frameworks capture complex couplings between finite deformation and mass transport, as demonstrated in hydrogel swelling and poroelastic media. Comparable multiphysics interactions are central to food structuring. For example, during high-moisture extrusion of plant-based meat analogs, flow-induced phase separation generates distinct microstructures, localized lubrication layers, and syneresis. Describing such complex behaviors exceeds traditional purely rheological or elastic models, demanding an integrated multiphysics approach combining mechanics, mass transport, thermal dynamics, and phase behavior.

Concurrently, advanced rheological formulations, particularly Thixotropic-Elasto-Visco-Plastic (TEVP) models, are indispensable for capturing history-dependent flow, structural breakdown, and yield dynamics in doughs, dense emulsions, and concentrated protein suspensions. Bridging TEVP rheology with finite-strain hyperelasticity and plasticity theory provides a robust foundation for modeling materials that continuously transition between flowing liquid-like states and load-bearing solid networks.

Incorporating moisture transport, thermal fields, phase separation, and microstructural evolution into a unified constitutive framework opens new horizons for predictive food modeling. Such integrative theories are essential for transitioning food process engineering from empirical trial-and-error toward rational, physics-based design.