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Climate change is generating several problems in wine technology. One of the main ones is lack of acidity and difficulties performing malolactic fermentation to stabilize wines before bottling. Among the different available acidity management technologies, such as direct acid addition, ion exchange resins, electro-membrane treatments, or vineyard management, the microbiological option is reliable and deeply studied. The main approach is the increase in malic acid content because of the metabolism of specific Saccharomyces strains and to increase lactic acid because of the metabolism of Lachancea genus. Other non-Saccharomyces yeasts, such as Starmerella bacillaris or Candida stellata can also acidify significantly because of the production of pyruvic or succinic acid. Wine industry needs the removal of malic acid in most red wines before bottling to achieve wine stability. Oenococus oeni performs the malolactic fermentation of red wines on most conditions because of the metabolization of malic acid into lactic acid. However, modern oenology challenges such as high ethanol concentrations, high pH or low levels of malic acid have made researchers to look for other options to reduce potential risks of deviation. Other wine-related microorganisms able to de-acidify malic acid have appeared as interesting alternatives for specific difficult scenarios. Lactiplantibacillus plantarum and Schizosaccharomyces genus make up nowadays the main studied alternatives.

Highlights • For the first time a study reports about hybrids yeast influence on Riesling wine. • For the first time a study compares different commercial hybrids yeast. • For the first time several specific aroma compounds are studied for hybrids yeast. • Some non volatile compounds are studied for hybrids yeast., The current study highlights the effects of intra- and interspecific hybrid yeasts of the genus Saccharomyces (S.) on the alcoholic fermentation and formation of aroma compounds in cool climate Riesling wines. Three different hybrid yeasts: S. cerevisiae × S. paradoxus (SC × SP), S. cerevisiae × S. kudriavzevii (SC × SK) and S. cerevisiae var. cerevisiae × S. cerevisiae var. bayanus (SC × SB) were investigated. The species S. cerevisiae var. bayanus (SB) was chosen as control variant. It has been demonstrated that the hybrid yeasts have the ability to preserve positive properties while, suppressing undesired properties from the parental yeast species. The hybrid SC × SK showed an increase of desired acetate esters and monoterpenes. The concentrations of higher alcohols were higher in wines fermented by SC × SP, compared to the other variants. SC × SP fermentations resulted in decreased concentrations of l-malate and sulphites.

This paper describes the selection of Schizosaccharomyces yeasts with adequate oenological suitability and high capacity for the degradation of malic acid. Despite the almost non-existent number of commercial strains, the use of this yeast genus has recently been recommended by the International Organisation of Vine and Wine (OIV, in French). Thus, in the present study, a large number of Schizosaccharomyces strains were isolated using a selective differential medium. Initially, classic parameters of oenological interest for the use of fermentative strains of Saccharomyces cerevisiae (the most frequently used type of yeast) were assessed. Only five strains of moderate acetic acid production lower than 0.4 g/L were obtained at the end of fermentation. Other, more specific features of this yeast genus' physiology were also studied, including urease activity and the production of pyruvic acid and glycerol. Finally, oenological suitability was determined by comparing selected strains with other Schizosaccharomyces reference and S cerevisiae control strains. Schizosaccharomyces strains produced 80% less urea content, four times higher pyruvic acid levels and 1 g higher glycerol contents than the Saccharomyces reference strains. The results confirmed that it is possible to perform selective processes on microorganisms from the genus Schizosaccharomyces using methodology developed in this work to obtain strains of industrial interest.

The recovery of underlying 3D particle size distributions by analyzing only 2D sections (such as thin layers or scanning electron microscopy images) has been thoroughly investigated in the last forty years. However, with the advent of increasingly more powerful computers, flexible programming languages and readily available source code, very interesting studies have recently been published on this topic. In this paper, we implement and discuss some key improvements to one particularly promising approach, which is based on the linear representation of the effect of each particle on the smaller apparent sizes that are measurable in the 2D plane. Two main improvements are examined: (i) the inclusion of either a parametric or a nonparametric fit to the measured data and (ii) the utilization of optimization tools to solve the resulting linear system. We endeavor to prove that the new method produces reliable results both in simulations and in an experimental validation example, while also reducing the number of required measurements.

Schizosaccharomyces pombe is a non-Saccharomyces yeast strain that can ferment grape musts with high sugar contents — but it also has other metabolic and physiological properties that render it of great interest to wine biotechnologists. This work compares the production of pyranoanthocyanins by S. pombe, Saccharomyces cerevisiae and Saccharomyces uvarum during fermentation. Total pyranoanthocyanins ranged from 11.9 to 19.4 mg/l depending on the strain of S. pombe used. On average, S. pombe produced more pyruvic acid than did either Saccharomyces species; as a consequence it also formed more vitisin A-type pigments. S. pombe 938 produced the largest quantity of vitisin A (11.03 ± 0.82 mg/l). The formation of large amounts of pyranoanthocyanins intensifies the post-fermentation colour of wines somewhat, a phenomenon that helps them maintain their colour over ageing as the natural grape anthocyanins become degraded. Some of the S. pombe strains showed hydroxycinnamate decarboxylase activity, which favours the formation of vinylphenolic pyranoanthocyanins. Fermentation with S. pombe therefore provides an interesting way of increasing the overall pyranoanthocyanin content of red wines, and of stabilising their colour during ageing.

The strains of two species of yeast, Saccharomyces cerevisiae and Pichia guillermondii , both with high hydroxycinnamate decarboxylase (HCDC) activity (56% and 90% respectively), were used in the fermentation of musts enriched with grape anthocyanins, to favour the formation of highly stable vinylphenolic pyranoanthocyanin pigments. The different strains were used to ferment the must separately, simultaneously, or sequentially, the latter involving an initial period using the yeast with the greatest HCDC activity ( P. guillermondii ). The must was made from concentrated grape juice diluted to 220 g/l of sugar, and enriched with grape anthocyanins to 100 mg/l and with p -coumaric acid to 120 mg/l. The pH was fixed to 3.5. All 50 ml micro-fermentations were done in triplicate. The development of anthocyanin-3- O -glucoside precursors, the decarboxylation of p -coumaric acid, and the formation of 4-vinylphenol and vinylphenolic pyranoanthocyanin derivatives were studied during the fermentation. The fermentation strategy used and the yeast HCDC activity significantly influenced the formation of vinylphenolic pyranoanthocyanins. The latter molecules were separated, identified, and quantified using high performance liquid chromatograph with diode array detection and electrospray-mass spectrometry (HPLC-DAD-ESI/MS). The volatile compounds profile was screened during fermentation using gas cromatogrphy-flame ionisation detection (GC-FID), in order to detect and quantify the main molecules. The best results were reached with the sequential fermentation (3.74 mg/l of malvidin-3- O -glucoside-4-vinylphenol). This work shows that during mixed or sequential fermentations carried out with non- Saccharomyces or highly fermentative Saccharomyces strains, with high HCDC activity, the content of stable pigments can be increased without sensorial modifications.

Different strains of Saccharomyces with different hydroxycinnamate decarboxylase (HCDC) activities, estimated by a bioconversion assay, were used for the fermentation of musts enriched with p -coumaric acid and grape anthocyanins, with the aim of favouring the formation of vinylphenolic pyranoanthocyanins, colour stabilization and (especially) the minimization of 4-ethylphenol. The development of anthocyanin-3-O-glucosides (precursors of vinylphenolic adducts), the decarboxylation of p -coumaric acid, and the formation of 4-vinylphenol, 4-ethylphenol and vinylphenolic pyranoanthocyanins were monitored by HPLC-DAD-ESI/MS. After fermentation, the wines were inoculated with large numbers (10 4 CFU/ml) of Dekkera bruxellensis to establish their potential for ethylphenol production. The HCDC activity of the strains significantly increased the formation of vinylphenolic pyranoanthocyanins and reduced the final concentration of 4-ethylphenol and 4-ethylguaiacol generated by the vinylreductase activity (VPhR) of D. bruxellensis . Early decarboxylation of hydroxycinnamates to vinylphenols, by means of Saccharomyces strains with strong HCDC activity, and their subsequent binding with anthocyanins to form stable pyranoanthocyanins, is a possible way to reduce the likelihood of ethylphenol production by Brettanomyces during in-barrel aging.

HPLC with refractive index detection (HPLC/RI) was used to study the autolytic release of polysaccharides from the cell walls of six strains of Saccharomyces cerevisiae and the commercial yeast species Sacch. uvarum in a model medium over a nine month period of ageing over lees. The effect of adding β-glucanase was also studied. In the presence of this enzyme autolysis was complete within 2–3 weeks; conventional autolysis needed to proceed for at least five months before large quantities of released polysaccharides could be detected. The final polysaccharide profile of the model medium obtained by enzyme-assisted autolysis was, however, different to that obtained by conventional autolysis, with more fragments of smaller molecular weight and a greater grouping of molecular sizes in the HPLC/RI peaks. The influence on the monomeric anthocyanin content of commercial red wines was examined by HPLC with photodiode array detection (HPLC/PDAD). Ageing over lees without enzymes appeared to have a protective effect on the total monomeric anthocyanin content, while the use of β-glucanase led to a large reduction in their concentration, probably via the undesirable activity of β-glucosidase impurities.