Edible soft matter in between fluid and solid states

The structuring of foods frequently requires materials to move between fluid-like and solid-like states during processing. Food needs to flow or deform to acquire a desired (micro)structure, but subsequently must become sufficiently solid-like to preserve that structure. Such transitions are central to processes as diverse as drying, baking, frying, extrusion and 3D food printing. They may result from gelation, glass transition, crystallization, changes in moisture content or temperature, or from the rebuilding of a microstructure after flow. Understanding how these changes in mechanical state emerge, and how they interact with transport and microstructural evolution, remains an important challenge in food physics and food engineering.

This Virtual Special Issue of Current Research in Food Science, entitled “Edible Soft Matter in between Fluid and Solid States”, originated from the symposium “Modelling Edible Soft Matter in between Solid and Fluid States”, organized in Wageningen in December 2024. The symposium brought together researchers working in food rheology, transport phenomena, soft-matter physics and solid mechanics to discuss the behaviour of foods during such transitions. Speakers were invited to contribute to the Special Issue, while additional authors who had not participated in the symposium subsequently broadened the scope of the collection. Consequently, the contributions cover a wide range of food materials and processes, but are connected by a common question: how does processing change the mechanical state and structure of edible soft matter?

A major theme emerging from the collection is the close relation between transport, changes in material properties and deformation. This is particularly evident during drying and other intensive heating processes, where removal or redistribution of water can substantially alter mechanical properties while simultaneously generating shrinkage and stresses. Hu et al. (2026) address this complexity with a multiphase and multiscale mechanistic model for hot-air drying of shiitake mushroom. Veser et al. (2025) focus on prediction of cabbage-seed drying at laboratory and industrial scale using a non-equilibrium sorption-isotherm approach, whereas Rizki et al. (2025) examine changes in material properties during electrohydrodynamic drying, with particular attention to the falling-rate period. Shah and Takhar (2026) consider an even more strongly coupled process, microwave frying, by combining unsaturated transport based on hybrid mixture theory with electromagnetic phenomena. Together, these studies illustrate that heat and mass transfer cannot always be considered independently from the evolving physical state of the food.

The interaction between moisture transport and mechanics becomes particularly apparent when deformation itself becomes part of the structuring process. van der Sman, Curatolo and Teresi (van der Sman, et al., 2025a) investigate buckling during drying of edible soft matter with a cylindrical core-shell geometry, showing how drying-induced mechanical instabilities can generate complex deformation. In another contribution, van der Sman, Curatolo and Teresi (van der Sman, et al., 2025b) explore programmable shape morphing during drying through symmetry breaking, illustrating that deformation induced by moisture gradients need not only be an unwanted consequence of processing, but may also be deliberately exploited for structure design. Grasa, Teresi and van der Sman (Grasa et al., 2025) address large-strain anisotropic behaviour of meat during cooking using finite-element modelling, thereby highlighting another situation in which mechanical deformation, material anisotropy and transport processes have to be considered together.

These studies point toward a broader development in food modelling. Food rheology has traditionally concentrated on materials in their flowing state, whereas the mechanical behaviour of foods undergoing large deformation in a more solid-like state has received comparatively less attention. At the same time, developments in soft-matter mechanics and poromechanics increasingly allow deformation, viscoelasticity and moisture transport to be described within thermodynamically consistent frameworks. A more detailed discussion of the emerging connection between rheological descriptions, elasto-viscoplastic models and large-deformation mechanics, as well as the role of stress-driven moisture migration, is provided in the recent review (van der et al., 2026).

At the other side of the fluid-solid transition are processes in which a food material must first flow in a controlled manner and subsequently preserve the generated shape. Three-dimensional food printing provides a particularly clear example. Kim et al. (2025) investigate the 3D printability and structural properties of plant-based scallop adductor-muscle analogues, relating these properties to amylose content and the pasting behaviour of different rice cultivars. Liu et al. (2025) study edible 3D-printed emulsion gels and examine how the incorporation of inulin influences their mechanical and sensory properties. Both studies demonstrate that printability cannot be considered simply as a question of viscosity: the material must possess an appropriate mechanical response during extrusion while recovering or developing sufficient structural integrity after deposition.

The mechanisms through which a material acquires this structural integrity can differ substantially between food systems. Renzetti et al. (2025) investigate cereal and tuber starches and identify hydrogen-bond density and glass-transition temperature as important factors governing gelatinization and gel rheology. This contribution emphasizes the connection between molecular interactions, thermal transitions and macroscopic rheological behaviour. In another class of materials, Holian, Bolton and Wilson (Holian et al., 2025) consider how structure can be generated in soft solids to obtain heat-stable milk chocolate. These studies illustrate that transitions between fluid-like and solid-like response ultimately originate in changes occurring over smaller length scales, ranging from molecular mobility and intermolecular interactions to the formation of mesoscopic networks.

Structured lipid systems provide further examples of this principle. Shuai et al. (2026) investigate rice-bran-wax-structured macadamia oleogels and temperature-responsive water-in-oil emulsions. Here, organization of the lipid phase provides a route to manipulating mechanical and functional properties. Rasouli Pirouzian et al. (Rasouli et al., 2025), in their study of sucrose-free probiotic dark chocolate, similarly address formulation in relation to rheological properties and functionality. Although these systems differ considerably from drying foods or printed gels, they share the same basic soft-matter principle: macroscopic material behaviour emerges from an evolving internal structure whose formation is controlled by composition and processing conditions.

Taken together, the contributions to this Special Issue show that the boundary between a fluid and a solid is not a sharply defined state for many foods. Rather, edible soft materials move continuously through liquid-like, viscoelastic, plastic and solid-like regimes as their microstructure evolves. Different physical mechanisms dominate in different systems. In some materials, a network is created by gelation or crystallization; in others, mobility is arrested by cooling or glass transition. In yield-stress and paste-like materials, flow disrupts an existing structure that can subsequently rebuild. During drying, cooking and frying, changes in moisture content may simultaneously alter mechanical properties and generate stresses and deformation.

Such behaviour also challenges the conventional separation between rheology and solid mechanics. Rheological models are particularly suited to describing flow, yielding, viscoelasticity and structural recovery, whereas large-deformation solid mechanics provides a natural framework for describing finite deformation and its coupling to solvent or moisture transport. Recent theoretical developments show that these viewpoints are more closely related than their historically separate development might suggest. In particular, the configuration tensor used in advanced rheological models has a direct counterpart in the Cauchy-Green tensor used in large-deformation mechanics, providing a possible common language for materials that alternate between flowing and solid-like states. The implications of this connection, including its relevance to elasto-viscoplastic food materials and stress-driven phase or moisture migration, are discussed in more detail in the aforementioned COFS review (van der et al., 2026).

The diversity of this Special Issue is therefore also one of its strengths. Drying of biological materials, frying, cooking of meat, 3D printing, starch gelatinization, chocolate structuring and oleogel formation may initially appear to represent rather separate research areas. Viewed as problems in edible soft matter, however, they share a common scientific challenge: understanding how processing changes microstructure and thereby moves a material between fluid-like and solid-like states, and how this evolving mechanical state determines the structure and functionality of the final food.

Future progress will require closer integration of experimental characterization and modelling across different length and time scales. Rheological and mechanical measurements must increasingly be combined with techniques capable of following changes in microstructure, moisture distribution and deformation during processing. At the same time, constitutive models should move beyond descriptions that reproduce material behaviour under a restricted set of conditions toward formulations that account for the evolution of internal structure and its coupling to deformation, temperature and moisture transport. Such approaches will ultimately provide a more predictive relation between formulation, processing conditions, structure and food functionality.

We hope that this Virtual Special Issue stimulates further exchange between food scientists, rheologists, physicists and researchers in soft- and solid-matter mechanics. The discussions initiated during the Wageningen symposium and subsequently broadened through the contributions to this collection demonstrate the opportunities arising from such cross-fertilization. Bringing these perspectives together should help move food structuring from predominantly empirical process-property relations toward a more mechanistic and predictive science.