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Wine clarity is a critical aspect in the commercialization of white wines. The formation of wine haze can be attributed to the aggregation and precipitation of heat-unstable wine proteins. Bentonite fining is the commonly used method in winemaking for protein removal, but it is responsible for loss of wine volume and quality. Dicarboxymethyl cellulose (DCMC) was developed as a potential alternative to bentonite. Water-insoluble DCMC was prepared via catalyzed heterogeneous etherification using sodium chloromalonate and potassium iodide. White wine fining trials were benchmarked with different dosages of DCMC against a bentonite. A high-performance liquid chromatography method was optimized for protein quantification. The samples underwent heat stability tests to evaluate wine turbidity before and after fining. Results show that DCMC successfully reduced the wine protein content and turbidity. DCMC produced heat-stable wines with dosages higher than 0.25 g/L. The innovative application of DCMC in the wine sector shows potential due to its ability to stabilize white wines while overcoming problems associated with bentonite, such as lees production and loss of wine, contributing to a more sustainable process. [ABSTRACT FROM AUTHOR]

Highlights • Bentonite and heat reduced wine protein content by the end of the fermentation. • Bentonite and heat had limited impact on wine tannin concentration. • Fermenting wines with pomace reduced tannin retention in Frontenac wines. • 3 g/L of enological tannins was needed to increase wine tannin concentration. • Wine tannin concentration cannot be improved from the use of berries alone. Abstract The impact of different factors (must protein treatment: bentonite and heat; pomace: fermented with and without; tannin addition: 0–9 g/L; and time of maceration: 0–11 days) on tannin, pigment, and protein extraction/retention in Frontenac wines was investigated. Wine tannin concentration and composition were determined by HPLC-fluorescence. Protein and pigment parameters were analysed by BCA assay and Boulton's method, respectively, using UV-spectrophotometry. Results: Bentonite and heat significantly reduced wine protein concentration at the end of alcoholic fermentation but heat was less efficient than bentonite (1.8–5.0 times less). Removing wine proteins did not improve tannin retention in wines (p > 0.1032) but fermenting without pomace significantly improved their retention (up to 2.4 times), especially that of polymeric flavan-3-ols (up to 27.8%). An addition of 3 g/L of enological tannins in wines, fermented with or without pomace, was necessary to increase wine tannin concentration significantly. [ABSTRACT FROM AUTHOR]

Aggregation of heat unstable wine proteins is responsible for the economically and technologically detrimental problem called wine protein haze. This is caused by the aggregation of thermally unfolded proteins that can precipitate in bottled wine. To study the influence of SO 2 in this phenomenon, wine proteins were isolated and thaumatins were identified has the most prone to aggregate in the presence of this compound. Isolated wine thaumatins aggregation was followed by dynamic light scattering (DLS), circular dichroism (CD), fluorescence spectroscopy and size exclusion chromatography (SEC). Our experimental results demonstrate that protein thermal unfolding after exposure of the protein to 70 °C does not present differences whether SO 2 is present or not. Conversely, when the protein solution is cooled to 15 °C (after heat stress) significant analytical changes can be observed between samples with and without SO 2 . A remarkable change of circular dichroism spectra in the region 220–230 nm is observed (which can be related to S-S torsion angles), as well as an increase in tryptophan fluorescence intensity (absence of fluorescence quenching by S-S bonds). Formation of covalently-linked dimeric and tetrameric protein species were also detected by SEC. The ability to dissolve the aggregates with 8 M urea seems to indicate that hydrophobic interactions are prevalent in the formed aggregates. Also, the reduction of these aggregates with tris (2-carboxyethyl) phosphine (TCEP) to only monomeric species reveals the presence of intermolecular S-S bonds. [ABSTRACT FROM AUTHOR]

Wine is a multi-attribute product and one of great differentiation. Consumers do not know wines' intrinsic properties before its purchase; consumers need and look for extrinsic signals that allow them to infer those intrinsic properties. To evaluate those intrinsic wine properties, the article uses price as an extrinsic signal to express their value. The price used is a comparison between the prices suggested by the specialized guides and the ones proposed directly to the consumer at the on-line stores. With the hedonic price methodology, which relates price and attributes, the article shows the convergence between the value referenced (price) by the Spanish experts and the one paid (price) in the Spanish market, the former being independent of the interests of the economic agents and the latter not. Regional reputation is the only attribute that positively impacts the price of Castilian wine and is prioritized in the ranking of attributes. [ABSTRACT FROM AUTHOR]

Mesoporous nanomaterials were used to prevent protein haze in Muscat Ottonel and Pedro Ximénez wines. Major volatile compounds, polyols and turbidity were analyzed in fined wines and the results were compared with untreated and fined with bentonite wines. Two commercial mesoporous nanomaterial labelled as SBA-15 and MCM−41 provided a notable turbidity reduction and prevent protein haze as was demonstrated by the heat stability tests. Only, the siliceous material labelled as KIT-6 was not suitable for wine fining. All the chemical families were affected by the fining agents, although the loss of aroma compounds was lower with nanomaterials than with bentonite. The impact on volatile compounds concentration depends on tested wine, independently on the fining agent used. Wines were distinguished by principal components analysis, which was carried out using the volatile compounds as classifying variables. Wines treated with SBA-15 were closest to the control wine in terms of volatile compounds concentration. [ABSTRACT FROM AUTHOR]

The stabilisation of the proteinaceous material in the wine matrix represents one of the big challenges for the production of quality white wines, but the characterisation of the mechanism that governs the interactions between its components is still a very challenging goal. The aim of this study was to provide new information for developing new technologies in the stabilisation of bottled white wines using a novel theoretical approach. This method combines electronic structure calculations for the determination of the a stable conformation of three ligands that may interact with one of the proteins responsible for the haze in wines, the thaumatin-like protein (TLP), with the search for the mode of binding between this protein and its ligands through docking calculations. The result shows that sites that exposed positive residues to the surface of the protein are the sites favoured for the caffeic acid (CA) binding. Additionally, it was observed that the ligand with the lowest binding energy (-7.38 kcal/mol) was the quercetin (Q). The presence of a π-π stacking interaction with the residue F118 is confirmed in a family of TLP-Q complexes, and it is proposed that the mechanism of haze formation in white wines during bottle storage seems to be related to the interaction of polyphenolic molecules with some residues of this big cavity; these residues or sites of interaction can be considered as future targets in the control of the haze phenomena and in the research on alternatives to the fining treatment in the wine industry. [ABSTRACT FROM AUTHOR]

Bentonite is the only fining agent which can stabilize wine and prevent protein haze formation after bottling. Currently many approaches are used to find an alternative because of bentonite's negative influence on color and aroma compounds. Nevertheless, the interaction of bentonite with wine proteins is not fully understood. Therefore, we analyzed the influence of a NaCa-combined bentonite on the protein content and composition of different wines showing a partial selectivity on protein adsorption. For example, glycosylated proteins were not removed by bentonite in notable amounts. Performing mass spectrometry we were able to demonstrate that 96% of class IV chitinase was adsorbed by bentonite, whereas varying adsorption behavior was observed for different thaumatin-like protein isoforms ranging from no removal to 98% of reduction. These differences may be explained by considering hydrophobicity surface of the proteins. Here, some differences are detected which might be an explanation for the better or worse adsorption. Our results demonstrate the importance to consider the isoforms of the potential haze-related proteins. Only the understanding of the interaction conditions of the wine component and their behavior with fining agents might result in the development of new strategies preventing protein haze formation. [ABSTRACT FROM AUTHOR]

Chitosan beads from a microbial source, i.e. Aspergillus niger (An), were produced by precipitation method for the first time and compared with supports prepared from an animal source, i.e. shellfish derived chitosan with three different molecular weights (low (LMW), medium (MMW) and high (HMW)). The produced beads were used as enzyme carriers to be applied in a continuous packed-bed reactor (PBR) for white wine protein stabilization. For this purpose, the beads were crosslinked with glutaraldehyde (GDH) and stem bromelain was immobilized on the carrier surface as a model enzyme, following two different procedures (i.e., crosslinking with glutaraldehyde (GDH) and direct linkage (DL)). Drop-like beads with an average diameter of 3.0–3.5 mm and a moisture content of 86–94% were obtained. The morphology of the produced beads in dried state, in terms of shape and surface, was studied by means of a scanning electron microscope (SEM), evidencing the obtainment of nearly spherical or oval particles. The efficacy of the crosslinking procedure and of bromelain immobilization was demonstrated by means of SEM investigation and infrared spectroscopy (FT-IR) analysis, revealing a rougher surface. Various initial protein concentrations ranging between 0.45 and 18.00 mg BSAeq mL −1 were tested in order to identify the optimal amount and to evaluate the influence of the initial concentration on the total protein loading. Stem bromelain proved to be more active when immobilized by DL on An beads and was efficient in reducing white wine hazing potential continuously, as verified with a laboratory bench-scale PBR. [ABSTRACT FROM AUTHOR]

Several wine quality aspects are influenced by yeast mannoproteins on account of aroma compounds retention, lactic-acid bacterial growth stimulation, protection against protein haze and astringency reduction. Thus selecting a yeast strain that produces high levels of mannoproteins is important for the winemaking industry. In this work, we observed increased levels of mannoproteins in S. cerevisiae × S. kudriavzevii hybrids, compared to the S. cerevisiae strain, in wine fermentations. Furthermore, the expression of a key gene related to mannoproteins biosynthesis, PMT1 , increased in the S. cerevisiae × S. kudriavzevii hybrid. We showed that artificially constructed S. cerevisiae × S. kudriavzevii hybrids also increased the levels of mannoproteins. This work demonstrates that either natural or artificial S. cerevisiae × S. kudriavzevii hybrids present mannoprotein overproducing capacity under winemaking conditions, a desirable physiological feature for this industry. These results suggest that genome interaction in hybrids generates a physiological environment that enhances the release of mannoproteins. [ABSTRACT FROM AUTHOR]

A set of seven commercial white wine samples (W1-7) produced from the cultivar Malagousia and obtained directly from the cellar 4 months after winemaking were subjected to accelerated oxidation (55 °C, 11 days). The correlation of browning susceptibility with compositional data, as well as the effect on phenolic content using simple assays, and the radical scavenging activity (DPPH, ABTS) were examined. Calculated browning rate constants ( k) varied by 1.03-2.66-fold among pairs of samples. Thus, despite the fact that samples originated from the same cultivar, differences were significant in some cases. No correlation was observed between browning and total or free sulfur dioxide, total iron, copper or other compositional parameters (total phenol, total hydroxycinnamates, total flavanol, catechin, epicatechin content, etc.), except for the grape reaction product/caftaric acid ratio (0.802, p = 0.017). The later suggested that wine must elaboration might be important for white wine oxidative stability, and its contact with oxygen should be avoided or minimized. Addition of ascorbic acid at the maximum level detected in the tested wines (70 mg/L), to one of the samples free of ascorbic acid but containing the highest level of total (100 mg/L) and free SO (30 mg/L) among these, had a negative effect. However, one of the samples containing ascorbic acid (33 mg/L) was resistant to oxidation. The molar ratio of free SO to that of ascorbic may affect browning susceptibility; therefore, the use of ascorbic acid should be made with caution. Chemometrics could be useful to provide prediction of browning susceptibility in relation to compositional data. The radical scavenging activity decreased with a significant correlation between the loss in DPPH scavenging and ascorbic acid content ( r = 0.845, p = 0.008). The changes in total flavanols did not follow a clear trend, whereas the spectrophotometric monitoring of total hydroxycinnamate was not informative due to interferences with browning products. Present findings are expected to be useful for those involved in white wine production. [ABSTRACT FROM AUTHOR]

Protein haze in white wines is a major technological and economic problem for the wine industry. In particular, an increased haze formation can be observed in wines from dry vintages. Therefore, field tests were carried out in steep slope vineyards planted with Riesling grapes over three dry growing seasons to study the effect of drought stress on the concentration of proteins in the resulting wines. Plots suffering from drought stress were compared with the surrounding drip-irrigated plots. Riesling grapes were processed into wines by conventional procedures. Protein amounts of the isolated wine colloids of the stressed samples (S) were always higher than those of the watered samples (W) (mean watered 13.8 ± 0.44, mean stressed 17.4 ± 0.40 g 100 g isolated colloids). As a consequence, higher bentonite doses were needed to achieve protein haze stability of the drought-stressed treatments. Concerning the protein composition, there were no significant differences between stressed and watered treatments. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed that the molecular weights of proteins ranged from 12 to 75 kDa with an accumulation of chitinases and thaumatin-like proteins between 20 and 30 kDa. Concerning the protein composition, minor differences became obvious only between vintages but not between the stressed and watered samples. In-solution digest of proteins from Riesling grapes 2008 followed by LC-MS and database research identified 15 proteins originating from grapes and 10 from the yeast Saccharomyces cerevisiae. In conclusion, our study demonstrates the importance to develop new strategies to prevent increased haze formation in wine under the predicted conditions of climate change. Prevention of drought stress by drip irrigation can be considered as one strategy to decrease protein amounts in wines. [ABSTRACT FROM AUTHOR]

Despite the extensive research performed during the last decades, the multifactorial mechanism responsible for white wine protein haze formation is not fully characterized. A model is proposed, which is essentially based on two postulates: the experimental identification of sulfur dioxide as the non-proteinaceous factor, and the inference from reliable data available in the literature of the dynamic chemistry played by wine protein sulfhydryl groups. Unlike other reducing agents, addition of SO 2 to must/wine upon heating cleaves intraprotein disulfide bonds, hinders thiol-disulfide exchange during protein interactions, and leads to formation of novel interprotein disulfide bonds. These bonds are ultimately responsible for wine protein aggregation following a nucleation-growth kinetic model, as shown by Dynamic Light Scattering experiments. The model was tested in wine model solution (using total and fractionated wine proteins) and validated under real wine conditions. The results achieved may open the way to develop techniques that will find wide application in the wine industry. [ABSTRACT FROM AUTHOR]

Wine producers have to label the use of certain animal proteins for fining of must and wine since 2012 [regulation (EC) No. 579/2012] under specific conditions, which has encouraged the search for alternative fining agents produced out of plants or yeasts. Yeast proteins are naturally present in wine and first studies of yeast protein extracts (YPE) for the fining of wine have been published, which were mainly focused on the technical properties of the YPE as fining agents. The present study used YPE of different production techniques for fining of red wine and evaluated their technical properties. Furthermore, the sensory effect of the new fining agents, their protein composition and the presence of glycans and glycoproteins were examined. The YPE showed differences in their protein profile and in protein glycosylation, but all YPE that were investigated were successfully applied for fining of red wine. Mannoproteins were detected in all YPE, and they did not prevent the mutual precipitation of proteins and tannins that is necessary for successful fining as reported earlier in case of glycans and glycoproteins. The chemical parameters of the red wine were modified by fining with YPE in a way comparable to fining with gelatine, a traditional fining agent used as reference, and the initial quality of wine flavour was maintained during the treatments. [ABSTRACT FROM AUTHOR]

Excessive amounts of protein in wine can lead to haze formation during wine-making. The use of bentonite reduces that risk by removing proteins. Most haze proteins have been identified to be pathogen related, as this fraction is formed as a reaction to stress and infection of the plant. These may be weather related. The aim of this study was to seek correlations between vintage variations and the demand for bentonite in German wines from the Palatinate region. Different climate-related influences and ripening parameters were evaluated to test potential correlations. A feasible link between environmental factors such as temperature, sunshine hours, solar radiation, precipitation, drought index, and water balance was discovered, which explains the amount of bentonite used. More than 1000 wine analyses were used to calculate the average requirement between 2001 and 2010. In years with lower demand, the number of unusual weather events was higher, so it can be inferred that weather anomalies reduce the need for bentonite. [ABSTRACT FROM AUTHOR]

Proteinogenic wine fining agents are hidden allergens and could present a risk for consumers with allergies. Therefore, the European Parliament adopted Directive 2003/89/EC amending Directive 2000/13/EC to declare ingredients, contaminations and processing aids that are known to trigger allergic reactions. The Amendment Regulation (EU) 1266/2010 excluded the labelling of wines which are processed with hen’s egg and products thereof until 30 June 2012 to get more scientific findings. After 1 July 2012 wine fining agents have to be declared if above 0.25 mg l–1(Regulation (EU) 579/2012 in conjunction with article 120 g of Regulation (EU) 1234/2007). The Organisation International de la Vigne et du Vin (OIV) advises this limit of detection (LOD) for potential allergenic residues of proteins. Wine fining agents are processing aids and according to the wine producer’s knowledge will be removed after coagulation by filtration or other production steps. Due to lack of scientific data, residues of fining agents in the final product could not be excluded. In this risk assessment, highly sensitive ELISA methods for ovalbumin of known origin for wine have been developed. The objective was to investigate the presence of allergen residues in wine after certain technological treatments were applied to remove the wine fining agents. For all developed ELISA methods the LODs are in the low µg l–1range between 5 and 10 µg l–1fining agent, whereas the LOQ varies between 5 and 80 µg l–1fining agent. The results of the investigation of well-known wines and fining agents demonstrate that white wines fined with white or ovalbumin from hen’s egg could retain allergens. The use of certain technological procedures during wine processing leads to different results. In white wine, bentonite or sheet filtration followed by sterile filtration lead to wines containing no detectable amounts of ovalbumin. In red wine, especially the final sterile filtration removes the fining agents. [ABSTRACT FROM PUBLISHER]

Protein denaturation in white wines results into a hazy suspension with precipitate formation, affecting negatively their commercialization. The aim of this study was to identify a number of non-protein factors of wines, which exhibit a modulating effect upon haze formation and interfere with protein precipitation in white wines, applying stepwise multiple regression analysis. The influence of intrinsic non-protein factors, including surface and groundwater quality, on protein haze formation assessed by the heat test was studied. Experiments were performed on 18 Sauvignon Blanc wines from six Chilean valleys. The influence of non-protein factors (pH, electrical conductivity [EC], total and volatile acidity, alcohol, free and total sulfur dioxide, total polyphenols, and chloride, sulfate, K, Na, Ca, Mg, and Fe concentrations) on haze response was evaluated by means of multiple regression analysis. Significant contribution (p < 0.05) of EC, sulfate and Fe concentrations to protein haze was found. Due to multi-collinearity between sulfate and Fe concentrations, the multi-linear model of haze response was reduced to: Haze = -184 + 2.95 x [Protein] - 62.3 x [Fe] + 0.17 x EC (ra = 0.901). Electric conductivities of wine and surface water were correlated (p = 0.037); good correlations were also found between sulfate concentrations in wine and surface water (p = 0.003), and groundwater (p = 0.022). No correlation was detected for Fe. This study elucidates that protein haze formation in white wine is a multi-factorial process. Iron, EC, and sulfate, in addition to protein itself, have to be considered as factors that modulate wine protein hazing. [ABSTRACT FROM AUTHOR]

Highlights: [•] High pressure (HP) treatments modify the secondary structure of wine proteins. [•] HP treatment may contribute to stabilising proteins in Sauvignon blanc wine. [•] Modifications in protein structure and thermal stability depend on HP intensity. [•] Haze formation in wine during storage could be delayed by HP. [Copyright &y& Elsevier]

Abstract: Champagne is a world-renowned French sparkling wine, which undergoes many steps (fermentation, aging …) for its elaboration. Various compounds might evolve during this winemaking process and thus modify its final quality. Here, we report the first proteome analysis of two standard commercial Champagne wines, using the powerful Combinatorial Peptide Ligand Library (CPLL) technique. Indeed, wine proteins are present in small amounts but they are key compounds, likely to impact on both foam quality and aroma behavior. Forty-three unique gene products were retrieved in a single-varietal champagne and a blended champagne. Several proteins from Vitis vinifera together with seven yeast proteins were undoubtedly identified in these Champagne wines. Biological significance: The main advantage of CPLLs was the detection of low abundance proteins despite the absence of purification or pre-concentration step. It is an important fact to take into account, since Champagne wines generally contain a low amount of proteins (5–10mg/L) that implies to usually concentrate wine proteins before 1D or 2D electrophoresis. Most Champagne proteins are grape and yeast glycoproteins which are considered as good foam “promoters”. Some of these proteins might also interact with wine aromas, and thus contribute to the overall quality of Champagne wines. This article is part of a Special Issue entitled: Proteomics of non-model organisms. [Copyright &y& Elsevier]

Background and Aims Protein instability has long been a technical issue in white wine production. The aims of this study were: to examine the variability of wine proteins from a single cultivar within a defined wine region over two vintages; and to investigate the correlation of the content of the total and individual proteins and protein haze with the bentonite dosage required for heat stability. Methods and Results Proteins in Sauvignon Blanc juices and wines from five selected Marlborough, New Zealand, vineyards with two pruning/training regimes (two- and four-cane vertical shoot positioned) were studied over two consecutive vintages. Proteins were quantified and characterised by Coomassie Brilliant Blue assay, sodium dodecyl sulfate polyacrylamide gel electrophoresis and sodium dodecyl sulfate capillary gel electrophoresis ( SDS-CGE). The bentonite requirement for wine protein stability was determined by bentonite fining coupled with a hot/cold test. One vineyard consistently showed the lowest protein concentration and bentonite requirement regardless of pruning treatment and vintage, whereas others varied with pruning treatment and/or vineyard site and/or vintage. Two prevalent juice protein peaks at 22 and 28 kDa in SDS-CGE corresponded to two main wine protein peaks at 22 and 26 kDa, respectively. The 26 kDa fraction was reduced and became heterogeneous after fermentation, while the 22 kDa fraction remained unaffected. There was a good correlation between bentonite requirement and the 26 kDa fraction ( R2 = 0.78). Conclusion The depletion of 26 kDa fraction in wine determined by SDS-CGE was a good indicator for protein stability by bentonite fining. Significance of the Study These results suggest that the method of protein quantification may have a strong influence on the utility of protein concentration measurement to predict the bentonite requirement of wine. [ABSTRACT FROM AUTHOR]

Our studies focused on the determinationof aggregation mechanismsof proteins occurring in wine at room temperature. Even if the winepH range is narrow (2.8 to 3.7), some proteins are affected by thisparameter. At low pH, the formation of aggregates and the developmentof a haze due to proteins sometimes occur. The objective of this workwas to determine if the pH impacted the conformational stability ofwine proteins. Different techniques were used: circular dichroismand fluorescence spectroscopy to investigate the modification of theirsecondary and tertiary structure and also SAXS to determine theirglobal shape. Four pure proteins were used, two considered to be stable(invertase and thaumatin-like proteins) and two considered to be unstable(two chitinase isoforms). Two pH values were tested to emphasize theirbehavior (pH 2.5 and 4.0). The present work highlighted the fact thatthe conformational stability of some wine proteins (chitinases) wasimpacted by partial modifications, related to the exposure of somehydrophobic sites. These modifications were enough to destabilizethe native state of the protein. These modifications were not observedon wine proteins determined to be stable (invertase and thaumatin-likeproteins). [ABSTRACT FROM AUTHOR]

Abstract: This work explores to what extent the aroma or the non-volatile fractions of red wines are responsible for the overall flavor differences perceived in-mouth. For this purpose, 14 samples (4 commercial and 10 reconstituted wines), were sorted by a panel of 30 trained assessors according to their sensory in-mouth similarities. Reconstituted wines were prepared by adding the same volatile fraction (coming from a red wine) to the non-volatile fraction of 10 different red wines showing large differences in perceived astringency. Sorting was performed under three different conditions: (a) no aroma perception: nose-close condition (NA), (b) retronasal aroma perception only (RA), and (c) allowing retro- and involuntary orthonasal aroma perception (ROA). Similarity estimates were derived from the sorting and submitted to multidimensional scaling (MDS) followed by hierarchical cluster analysis (HCA). Results have clearly shown that, globally, aroma perception is not the major driver of the in-mouth sensory perception of red wine, which is undoubtedly primarily driven by the perception of astringency and by the chemical compounds causing it, particularly protein precipitable proanthocyanidins (PAs). However, aroma perception plays a significant role on the perception of sweetness and bitterness. The impact of aroma seems to be more important whenever astringency, total polyphenols and protein precipitable PAs levels are smaller. Results also indicate that when a red-black fruit odor nuance is clearly perceived in conditions in which orthonasal odor perception is allowed, a strong reduction in astringency takes place. Such red-black fruit odor nuance seems to be the result of a specific aroma release pattern as a consequence of the interaction between aroma compounds and the non-volatile matrix. [Copyright &y& Elsevier]

Bentonite fining to remove protein is the most widely used treatment to prevent protein haze in white wines. Bentonite can be added at different stages during winemaking. This study aimed to determine the best time to add bentonite. Unstable juices were vinified after bentonite fining of juice, or with bentonite added either early or late in fermentation. Different addition rates of bentonite were used and bentonite was either added in one or two additions. Fermentation rates were observed and protein stability and bentonite fining rates of the resultant wines were determined. Adding bentonite during fermentation or fining finished wines was the most efficient option in terms of amounts of bentonite required. Fermenting with bentonite present also may increase fermentation rates. Using the least bentonite necessary for heat stability is important for winemakers for quality, cost and environmental reasons. This study describes ways in which bentonite addition rates can be minimised. [ABSTRACT FROM AUTHOR]

White wines are stabilised by removing the heat unstable proteins through adsorption by bentonite. Bentonite fining is not an efficient wine processing step and can also remove other wine components. Alternative absorbents are thus sought; zirconium dioxide (zirconia) is recognised as a promising candidate. The aim of this work was to assess the viability of zirconia treatments to stabilise white wines, with particular attention on process development. Effective treatment was achieved by enclosing zirconia pellets into a metallic cage submerged in the wine. With this method, the wine could be treated with the adsorbent for the time required for protein stabilisation, and then removed without further manipulation. Zirconia treatments of three unstable wines partially or fully stabilised them without detectable modifications of their physicochemical parameters and colours, apart from the removal of metals and some acids, particularly when wines were treated for long times and with high dosages of the adsorbent. A simple and inexpensive zirconia regeneration method was also developed. The zirconia application to wine was very effective in removing proteins, and the proposed regeneration procedure could facilitate the uptake and development of zirconia-based solutions for the wine industry. This study confirmed the effectiveness of zirconia in removing wine proteins and demonstrated that the proposed method of application has the potential to become a viable alternative to bentonite. [ABSTRACT FROM AUTHOR]