Although bioprotection is now recognised as an alternative to SO₂ for limiting microbial spoilage, it does not guarantee protection against oxidation. This limits its application, more specifically for rosé winemaking. Oenological tannins present antioxidant properties, which could represent an interesting alternative to SO₂ to protect must and wines against oxidation. A combination of the inoculation of a bioprotectant yeast strain and the addition of oenological tannins was tested to eliminate sulfites during the pre-fermentative step of rosé winemaking. In this experiment carried out in a winery, two oenological tannins were compared: quebracho and gall nut tannins. The antioxidant efficiency of tannins was compared to that of SO₂. Colorimetric assays associated with chemical analyses of anthocyanins and phenolic compounds confirmed that the use of bioprotection alone did not protect the wine from oxidation. An addition of oenological tannins on musts stabilized the colour of bioprotected rosé wine in a similar way that SO₂ addition did. Quebracho tannins appeared more efficient than gall nut tannins. The colour differences observed cannot be explained either by the concentration or forms of anthocyanins. However, the addition of tannins led to better protection of oxidation-sensitive phenolic compounds comparable to that obtained with the addition of sulfites.

Background and Aims. If bioprotection has already been proven to limit the development of spoilage flora on musts, its effectiveness against oxidation depends on the winemaking process. To optimize its application, this study analyzed the evolution of the chemical composition of the bioprotected musts and wines, according to different settling routes. Their impacts on the organoleptic characteristics of wines were also studied. Methods and Results. A bioprotected must was subjected to 6 different maceration routes before AF (triplicates), varying the duration and temperature parameters. A temperature value 12°C was the main factor independently of the duration which allowed a good implantation of the bioprotectant. An increase of the maceration duration at 12°C led to browning of the must, without significant effect on the final color of the wine, which was felt as more floral, with more length in the mouth. Conclusions. The bioprotectant implantation and its effectiveness on the sensory profile of the wine was guaranteed at maceration temperature values lower than 12°C. Significance of the Study. This study participates in the improvement of the bioprotection management in white winemaking, with the guarantee of a positive impact of the prefermentation maceration without sulphites on the organoleptic profile of the wines.

As a biological alternative to the antimicrobial action of SO₂, bioprotection has been proposed to winemakers as a means to limit or prevent grape musts microbial alteration. Competition for nitrogenous nutrients and for oxygen are often cited as potential explanations for the effectiveness of bioprotection. This study analyses the effect of a bioprotective M. pulcherrima strain on the growth of one H. valbyensis strain and one H. uvarum strain. Bioprotection efficiency was observed only against H. valbyensis inoculated at the two lowest concentrations. These results indicate a potential species-dependent efficiency of the bioprotective strain and a strong impact of the initial ratio between bioprotective and apiculate yeasts. The analysis of the consumption of nitrogen compounds revealed that leucine, isoleucine, lysine and tryptophan were consumed preferentially by all three strains. The weaker assimilation percentages of these amino acids observed in H. valbyensis at 24 h growth suggest competition with M. pulcherrima that could negatively affects the growth of the apiculate yeast in co-cultures. The slowest rate of O₂ consumption of H. valbyensis strain, in comparison with M. pulcherrima, was probably not involved in the bioprotective effect. Non-targeted metabolomic analyses of M. pulcherrima and H. valbyensis co-culture indicate that the interaction between both strains particularly impact lysin and tryptophan metabolisms.

To date, there are no specific guidelines for the use of bioacidifying yeasts in winemaking. In this work, we aimed to characterize an oenological strain of Lachancea thermotolerans (Lt), a non-Saccharomyces lactic acid-producing yeast, and to test different sequential inoculation conditions with Saccharomyces cerevisiae (Sc). The results of bench scale vinifications showed that both the strategy of inoculating Sc 12 h after Lt and the mixing of Lt and Sc during fermentation delivered an acceptable increase in lactic acid (2 g/L) and a decrease in pH (about 0.15 units). Therefore, both strategies were implemented in winery experiments. Our results at the cellar scale showed no increase in acidity, which was likely due to the presence of indigenous yeasts. Overall, our experience shows the difficulty of translating laboratory protocols into cellar experiments and calls for further research into new strategies for implementing acidifying yeasts.

Interest in Metschnikowia (M.) pulcherrima is growing in the world of winemaking. M. pulcherrima is used both to protect musts from microbial spoilage and to modulate the aromatic profile of wines. Here, we describe the isolation, characterization, and use of an autochthonous strain of M. pulcherrima in the vinification of Chasselas musts from the 2022 vintage. M. pulcherrima was used in co-fermentation with Saccharomyces cerevisiae at both laboratory and experimental cellar scales. Our results showed that M. pulcherrima does not ferment sugars but has high metabolic activity, as detected by flow cytometry. Furthermore, sensory analysis showed that M. pulcherrima contributed slightly to the aromatic profile when compared to the control vinifications. The overall results suggest that our bioprospecting strategy can guide the selection of microorganisms that can be effectively used in the winemaking process.

The phenomenon of global warming has been demonstrated to induce the premature ripening of grapes, resulting in a concomitant increase in sugar and a decrease in acidity. This can result in the production of wines that are characterised by an imbalance in terms of alcohol content and acidity. The utilisation of lactic acid-producing Lachancea thermotolerans yeast in fermentation represents a promising strategy for reducing the pH of must without the need for chemical acidification. However, it is important to note that the fermentation rate and lactic acid production can be influenced by several factors present in the must. The present study focused on the effect of copper, utilised in organic vineyards to limit mildew, on biomass and lactic acid production by two L. thermotolerans oenological strains in laboratory-scale fermentations. The results obtained demonstrated that the addition of copper resulted in increased lactic acid production in comparison with the control condition and this effect was strain-dependent. The results of the microbiological follow-up, which was carried out using classical microbiological methods in conjunction with flow cytometry, demonstrate discrepancies in the fermentation kinetics in conditions exhibiting varying concentrations of copper. Furthermore, the analysis of the samples using flow cytometry revealed the oxidative status of the two strains throughout the fermentation process. Transcriptomic data indicates that certain metabolic pathways of L. thermotolerans are induced by the presence of copper, with hypothesises about ribosomal and parietal activities in addition to cell communication. The findings of this study demonstrate strain-specific effects of copper on L. thermotolerans, which may be of interest to winemakers, particularly those engaged in organic viticulture who intend to utilise acidifying yeasts during warm vintages.