Scientists Map the Fluid-Solid Frontier That Shapes Every Food We Eat

Every act of cooking, drying, baking, frying, extruding or three-dimensionally printing a food depends on a deceptively simple physical event: an edible material passing from a fluid-like state to a solid-like one, or back again. A dough must flow into a mold and then set; a mushroom slice must lose water and stiffen; a molten chocolate must harden into a glossy bar. Yet for something so universal, the mechanics of this fluid-solid transition in foods remains surprisingly poorly understood. A new Virtual Special Issue of Current Research in Food Science, entitled Edible Soft Matter in between Fluid and Solid States, brings together research from food rheology, transport phenomena, soft-matter physics and solid mechanics to confront the question directly. The collection grew out of a symposium organized in Wageningen in December 2024, Modelling Edible Soft Matter in between Solid and Fluid States, and has been broadened by contributions from authors well beyond the original meeting, creating one of the most comprehensive snapshots to date of how processing rewrites the mechanical state of what we eat.

The central insight running through the collection is that foods rarely sit comfortably on either side of the fluid-solid divide. Instead, they travel continuously through liquid-like, viscoelastic, plastic and solid-like regimes as their internal microstructure evolves. In some materials, a network is born through gelation or crystallization; in others, molecular mobility is frozen out by cooling or a glass transition. In yield-stress materials such as pastes, flow destroys a pre-existing structure that then rebuilds. During drying, cooking and frying, changes in moisture content can simultaneously alter mechanical properties and generate internal stresses and deformation. This continuous, mechanism-dependent journey between states is precisely why food structuring has historically been treated empirically, with process-property relationships assembled through trial and error rather than derived from first principles.

A major theme of the Special Issue is the tight coupling between transport processes, changing material properties and mechanical deformation, particularly during drying. Hu and colleagues present a multiphase, multiscale mechanistic model for hot-air drying of shiitake mushroom, capturing how water removal reshapes the material while it shrinks and stresses. Veser and co-workers predict cabbage-seed drying at laboratory and industrial scales using a non-equilibrium sorption-isotherm approach, while Rizki and colleagues track material-property changes during electrohydrodynamic drying with a close look at the falling-rate period, the stage where moisture loss slows and the material stiffens most dramatically. Shah and Takhar push the coupling even further in microwave frying, combining unsaturated transport based on hybrid mixture theory with electromagnetic equations. Together, these studies make a forceful case that heat and mass transfer cannot be modeled independently of the evolving physical state of the food.

Deformation itself can become a tool rather than a nuisance, and several contributions exploit this deliberately. van der Sman, Curatolo and Teresi investigated buckling during the drying of edible soft matter with a cylindrical core-shell geometry, showing how drying-induced mechanical instabilities generate intricate, predictable deformation patterns. In a companion study, the same team demonstrated programmable shape morphing during drying through symmetry breaking, effectively using moisture gradients to sculpt foods into designed shapes rather than accepting warping as a processing defect. Grasa, Teresi and van der Sman extended the coupled transport-mechanics framework to large-strain anisotropic behavior of meat during cooking using finite-element modeling. These works signal a shift in the field: instead of treating shrinkage, curling and buckling as quality problems to suppress, researchers are beginning to engineer them for structure design.

Underlying this shift is a broader theoretical realignment. Food rheology has traditionally concentrated on materials in their flowing state, while the mechanics of foods undergoing large deformations in a more solid-like condition received comparatively little attention. Meanwhile, advances in soft-matter mechanics and poromechanics now allow deformation, viscoelasticity and moisture transport to be described within thermodynamically consistent frameworks. A particularly striking conceptual bridge is the mathematical correspondence between the configuration tensor used in advanced rheological models and the Cauchy-Green tensor used in large-deformation mechanics. This equivalence offers a common language for materials that alternate between flowing and solid-like states, and its implications for elasto-viscoplastic food materials and stress-driven moisture migration are explored in a recent review by van der Sman in Current Opinion in Food Science. The practical consequence could be a new generation of models that predict, rather than merely reproduce, how foods behave through their whole processing journey.

At the opposite end of the fluid-solid transition lie processes in which a material must first flow in a controlled manner and then preserve its generated shape, and nowhere is this clearer than in three-dimensional food printing. Kim and colleagues examined the printability and structural properties of plant-based scallop adductor-muscle analogues, relating performance to amylose content and the pasting behavior of different rice cultivars. Liu and co-workers studied edible three-dimensionally printed emulsion gels, showing how inulin incorporation modifies both mechanical and sensory properties. Both studies converge on a key conclusion: printability is not simply a question of viscosity. A printable food must respond appropriately during extrusion, then recover or develop enough structural integrity after deposition to hold its printed geometry, a dual requirement that demands careful control across the entire fluid-solid spectrum.

The mechanisms by which foods acquire that structural integrity vary enormously across systems, and the Special Issue maps this diversity down to the molecular scale. Renzetti and colleagues investigated cereal and tuber starches, identifying hydrogen-bond density and glass-transition temperature as governing factors in gelatinization and gel rheology, thereby linking molecular interactions and thermal transitions directly to macroscopic mechanical behavior. On a different front, Holian, Bolton and Wilson explored how structure can be generated in soft solids to produce heat-stable milk chocolate, a formulation challenge that hinges on managing the solid-fat network so the product survives warming without collapsing. Both studies underscore that transitions between fluid-like and solid-like response ultimately originate at smaller length scales, from molecular mobility and intermolecular interactions up to the formation of mesoscopic networks that carry load.

Structured lipid systems offer further illustration of the same soft-matter principle. Shuai and colleagues investigated rice-bran-wax-structured macadamia oleogels and temperature-responsive water-in-oil emulsions, showing how organization of the lipid phase provides a route to tuning mechanical and functional properties, including delivery of bioactive compounds such as astaxanthin. Rasouli Pirouzian and co-workers, in their study of sucrose-free probiotic dark chocolate, addressed formulation optimization in relation to rheological characteristics and the viability of Saccharomyces boulardii. Although oleogels and functional chocolates sit far from drying mushrooms or printed gels on the supermarket shelf, they obey the same underlying rule: macroscopic material behavior emerges from an evolving internal structure whose formation is dictated by composition and processing conditions. This unity of principle is what makes the cross-disciplinary framing of edible soft matter so productive.

Taken together, the contributions point to a future in which food structuring moves from empirical process-property relations toward a genuinely mechanistic and predictive science. Achieving that will require closer integration of experimental characterization and modeling across length and time scales, with rheological and mechanical measurements increasingly combined with techniques that track microstructure, moisture distribution and deformation in real time during processing. Constitutive models, in turn, must evolve beyond reproducing behavior under narrow conditions toward formulations that capture the evolution of internal structure and its coupling to deformation, temperature and moisture transport. The Wageningen symposium and the resulting collection demonstrate the value of bringing food scientists, rheologists, physicists and solid-matter mechanicians to the same table. If that cross-fertilization continues, the next generation of foods may be designed, on paper, from the flow and setting behavior of their molecular ingredients upward.

Subject of Research: The fluid-to-solid state transitions of edible soft matter during food processing

Article Title: Edible soft matter in between fluid and solid states

Article References: Edible soft matter in between fluid and solid states. (n.d.). https://doi.org/10.1016/j.crfs.2026.101561

Image Credits: AI Generated

DOI: 10.1016/j.crfs.2026.101561

Keywords: edible soft matter, food rheology, food drying, 3D food printing, gelatinization, glass transition, oleogels, moisture transport, large-deformation mechanics, food structure, buckling, chocolate structuring