Using an innovative measurement technique, researchers at the Physics Laboratory of ENS de Lyon (LPENSL, CNRS / ENS de Lyon) have succeeded in precisely tracking the steps characterizing the transformation of milk into cheese, which could deepen our understanding and help optimize the mechanisms at work in the manufacture of the many cheeses that happily garnish our plates.

Abstract

Colloidal gels undergo a phenomenon known as physical aging, i.e., a continuous change of their physical properties with time. To date, most of the research effort on aging in gels has been focused on suspensions of hard colloidal particles. In this Letter, we tackle the case of soft colloidal “micelles” comprised of proteins, in which gelation is induced by the addition of an enzyme. Using time-resolved mechanical spectroscopy, we monitor the viscoelastic properties of a suspension of colloidal micelles through the sol-gel transition and subsequent aging. We show that the microscopic scenario underpinning the macroscopic aging dynamics comprises two sequential steps. First, the gel microstructure undergoes rapid coarsening, as observed by optical microscopy, followed by arrest. Second, aging occurs solely through a contact-driven mechanism, as evidenced by the square-root dependence of the yield stress with the elastic modulus measured at different ages of the gel. These results provide a comprehensive understanding of aging in enzymatic milk gels, crucial for a broad range of dairy products, and for soft colloids in general.

Reference
Two-step aging dynamics in enzymatic milk gels. Julien Bauland, Gouranga Manna, Thibaut Divoux, and Thomas Gibaud. Phys. Rev. Materials, July 9, 2024.
DOI : 10.1103/PhysRevMaterials.8.L072601
Open archive arXiv: 10.48550/arXiv.2403.10176