Liquid relative permeability through foam-filled porous media: Experiments

International audienceFor some applications involving liquid foams, such as soil remediation for example, the liquid relative permeability of the foam-filled porous medium is a crucial parameter as it sets the liquid flow rate at which active substances or nutrients (for bacteria) can be delivered deep into the medium. We are interested in the liquid relative permeability of foam-filled porous media, within the range of low liquid saturations, i.e., ≲ 20 vol % . We fill porous media (packed spherical grains) with different foams made from either alkyl polyglucosides (APG) or saponin, in such a manner that we obtain highly controlled samples in terms of the bubble-to-grain size ratio r and the liquid saturation. The liquid relative permeability of saponin samples exhibits an optimal value as a function of r, while it increases significantly for APG foams. The ratio of their relative permeability of APG/saponin reveals two regimes as a function of r: for r ≲ 0.25, the permeability ratio is equal to the ratio corresponding to the bulk foams, while for larger r values, the permeability ratio is increased by one order of magnitude. The foam microstructure changes a lot as the bubble-to-grain size ratio increases up to 0.5, so that a new liquid network is activated, made of surface channels and liquid bridges, the former connecting the latter even at low liquid saturation. These new liquid elements may greatly benefit foams with mobile interfaces such as APGs. One such issue would deserve a dedicated study to be elucidated

Daisy-shaped liquid bridges in foam-filled granular packings

International audienceHypothesis: Many applications of liquid foams use them to fill the porosity of various granular media. How is the liquid distributed in such foam-filled systems, in which the geometry of the bubble assembly can be strongly constrained by pore confinement? Experiments: We study how the liquid is distributed in a grain packing filled with liquid foam, as a function of both liquid content and bubble-to-grain size ratio. Moreover, Surface Evolver simulations are carried out at the scale of a single bubble confined into a tetrahedral pore. Findings: We reveal that foam-filled granular assemblies exhibit a robust pendular-like regime, which is reminiscent of the pendular regime in unsaturated media. The main difference is that here the liquid bridges are daisy-shaped, i.e. with a liquid core bounded by bubbly petals. A simple theoretical model is proposed to describe the foam liquid bridges between contacting grains. In the case of large bubbles, the model is compared with the Surface Evolver simulation. The model is also applied to the case of wall liquid bridge, which is compared with the experimental observation. Beyond their geometrical characteristics, the presence of these liquid bridges, which can represent almost 25% of the liquid contained in the porosity, makes it possible to imagine a new approach (binder foam-based) to bind granular assemblies and turn them to solid materials

Appl Microbiol Biotechnol

Non-Saccharomyces (NS) species that are either naturally present in grape must or added in mixed fermentation with S. cerevisiae may impact the wine's chemical composition and sensory properties. NS yeasts are prevailing during prefermentation and early stages of alcoholic fermentation. However, obtaining the correct balance between S. cerevisiae and NS species is still a critical issue: if S. cerevisiae outcompetes the non-Saccharomyces, it may minimize their impact, while conversely if NS take over S. cerevisiae, it may result in stuck or sluggish fermentations. Here, we propose an original strategy to promote the non-Saccharomyces consortium during the prefermentation stage while securing fermentation completion: the use of a long lag phase S. cerevisiae. Various fermentations in a Sauvignon Blanc with near isogenic S. cerevisiae displaying short or long lag phase were compared. Fermentations were performed with or without a consortium of five non-Saccharomyces yeasts (Hanseniaspora uvarum, Candida zemplinina, Metschnikowia spp., Torulaspora delbrueckii, and Pichia kluyveri), mimicking the composition of natural NS community in grape must. The sensorial analysis highlighted the positive impact of the long lag phase on the wine fruitiness and complexity. Surprisingly, the presence of NS modified only marginally the wine composition but significantly impacted the lag phase of S. cerevisiae. The underlying mechanisms are still unclear, but it is the first time that a study suggests that the wine composition can be affected by the lag phase duration per se. Further experiments should address the suitability of the use of long lag phase S. cerevisiae in winemaking