Modelling of mass transport and mechanics around an expanding gas bubble in semi-hard cheese

International audience; Bubbles in number and size are part of the sensory evaluation by the consumer at purchasing and eating Swiss-type cheese. To better understand the formation of eyes in cheese, comprehensive knowledge of the transport phenomena including mechanics and gas production is required. The aim of the present study was to investigate both the momentum transport occurring around a bubble and the way the production of carbon dioxide and its diffusion locally affects the bubble growth during cheese ripening. A model was developed and fed with parameters (gas production and mechanical parameters) that were measured on the same cheese loaf as the one used for experimental validation. The mechanics and gas transport phenomena included in the model were validated independently. For mechanical validation, bubble volume as well as deformation of the upper surface of the cylinder were dynamically assessed by MRI within the same experiment. Uncertainties on these measurements were estimated, and used as an additional criterion at the validation step of the model. A first sensitivity analysis was performed on the mechanical parameters using Sobol indices method to better understand the influence of mechanics on bubble growth. A sensitivity study of the bubble growth to mass transport parameters was performed and simulations were compared to the growth of bubbles as measured on industrial blocks. Simulated data were in good agreement with simulations, validating the adequacy of the mechanical model and the range of diffusivity applicable to well describe the actual bubble growth in cheese blocks. As expected, the bubble growth was mainly driven by the viscous part of the viscoelastic model and gas production and transport were found to control bubble growth in the Semi-hard cheese under study.