White wine continuous protein stabilisation: industrial viablity

Identifier:  TDX:338

Handle: https://hdl.handle.net/20.500.11797/TDX338

Authors:  Salazar González, Fernando Noé

Abstract:
Heat-unstable soluble proteins in grapes, grape juices and wines may become insoluble and precipitate causing the formation of undesirable hazes or deposits in white wines after bottling and during storage. <br/>Proteins are commonly prevented from forming hazes with bentonite, though this technique does have drawbacks: for example, the sensory properties of the wine are affected adversely because flavour compounds are removed and wine volume is lost as lees because of the swell and settling of the bentonite. In addition, the handling and disposal of spent bentonite continues to be a concern, because it involves high labour input and the associated costs, occupational health and safety issues, and the wine industry's environmental responsibilities and legislative requirements. It is estimated that the cost of bentonite fining to the wine industry worldwide is in the order of US$300-500 m per annum. Alternative fining technologies to bentonite, which are economically viable and maintain wine quality, are currently being sought. However, no successful techniques have been developed to date: all the attempts so far have either affected the quality of the wine or not been economically viable under standard winemaking conditions. Therefore, research on the implementation of new practices that have a less negative impact on the environment and are economically viable is particularly challenging.<br/>For this reason the aim of this thesis was to study the industrial viability of an alternative technology to bentonite fining which enables unstable proteins to be removed from white wines using zirconia as the adsorbent material. We also attempted to develop a continuous process, which stabilizes wine protein without having any negative effects on the physicochemical and sensory properties of the wine. Likewise we tried to make the process have a lower environmental impact by testing various regenerative treatments of the adsorbent material.<br/>First we studied the structure, morphology and surface properties of the zirconia and its capacity to remove unstable proteins from white wine versus thermal and chemical regeneration treatments. Subsequently we compared the physicochemical and sensory properties of a white wine fined by zirconia and bentonite. <br/>To further our understanding of the effect on membrane fouling and wine protein stability, we developed a hybrid process consisting of in-column adsorption with crossflow microfiltration. We also applied this new method to stabilize the base sparkling wine and compared the results with the conventional method of using bentonite as the fining agent to see the effects of the treatments on the foam quality and protein fractions. Finally, we applied the new method on an industrial scale by packing zirconia into a fixed bed column and by using the batch and continuous systems.<br/>The results show that the zirconia can be regenerated by thermal and chemical treatments, and that its physical, morphological and chemical properties are not altered. In fact its protein adsorption capacity can increase probably because some compounds or active centres derived from wine proteins are absorbed.<br/>The hybrid process was used to increase the permeate flux during crossflow microfiltration and stabilize wine proteins. We observed that proteins were reduced when the zirconia column adsorption was used during the crossflow microfiltration. Therefore both processes may act together.<br/>By comparing the physicochemical and sensory analyses of white wine proteins stabilized by zirconia and bentonite, we found that results were best when zirconia was used.<br/>The continuous protein stabilization of white wines by zirconia may also be useful for stabilizing proteins in base sparkling wines. Treating base sparkling wines with zirconia definitely gives better foam quality than with bentonite. <br/>Finally the results obtained in our industrial scale experiment showed that white wine continuous protein stabilization with zirconia as the adsorbent material is not only viable in both the continuous and batch systems, it also leaves the quality of the wine unchanged.