Towards continuous wine fining: Materials characterisation and crossflow performance testing of polymer-bentonite mixed matrix membranes

This study investigates the feasibility of using bentonite-embedded mixed matrix membranes to perform wine fining on white wines to eliminate protein instability. Membranes made using polyethersulphone or polyvinylidene fluoride were fabricated using the wet phase inversion technique and used to filter unfined New Zealand Sauvignon Blanc wine in a crossflow filtration system. The morphologies of all the fabricated membranes were characteristic of asymmetric phase inversion membranes. Confocal laser scanning microscopy analysis on the membranes suggests that the two major mechanisms of protein removal are adsorption by the embedded bentonite particles and size exclusion via the membrane morphology. Polyethersulphone membranes were found to produce wine of similar levels of protein stability (around 90% protein removal) and polyphenol content as polyvinylidene fluoride membranes of the same membrane composition and operating conditions but with as much as 80% higher flux. Stabilising wine in one filtration pass was possible with polyethersulphone membrane with 25 wt% bentonite while maintaining high flux. These promising results show that the tested process has the potential to replace the current batch-wise fining process with continuous crossflow membrane filtration with benefits such as increased processing speed and reduced wine loss.