The combined use of steam-treated bentonites and natural zeolites in the oenological refining process

Industrial minerals, particularly bentonites, have long been used in treatments to improve the stability andshelf life of white wines. We evaluated a new combination of rocks and minerals, including steam-treatedbentonites and natural zeolites (chabazite and phillipsite), to greatly reduce the risk of protein and tartaricinstability of wines. Detailed mineralogical, chemical and electrokinetic studies of these materials wereconducted using powder X-ray diffraction (PXRD), X-ray fluorescence (XRF), microporosimetry, BETsurface-area analysis and zeta-potential measurements. Several model wine solutions containing BovineSerum Albumin (BSA) were prepared to evaluate the oenological performance of the rock/mineralcombinations. UV-VIS spectrophotometry and ion chromatography were used to evaluate the degree ofwine stabilization from the protein and tartaric point of view.The experimental results showed that steam treatment modifies both the microporosity and externalsurface area of the bentonite. These changes in surface area, along with creation of hydrophobic surfaces,significantly modified the behaviour of the steam-treated bentonites, requiring an increase in the amount ofmaterial necessary to bring the protein content to required levels. An important benefit derived from the useof steam-treated bentonites is that the pre-mixing with water before addition to wine is not necessary, as thematerial is readily dispersed. Finally, the addition of natural zeolites effectively decreased the potassiumcontent, thereby improving the tartaric stability of white wines. In addition, this procedure results in minimalwaste, as the bentonite-zeolite mixture can be reused as soil amendments in agriculture.