Oxygen Incorporation and Dissolution During Industrial-Scale Red Wine Fermentations

Bio-protection in oenology by Metschnikowia pulcherrima: from field results to scientific inquiry

Finding alternatives to the use of chemical inputs to preserve the sanitary and organoleptic quality of food and beverages is essential to meet public health requirements and consumer preferences. In oenology, numerous manufacturers already offer a diverse range of bio-protection yeasts to protect must against microbiological alterations and therefore limit or eliminate sulphites during winemaking. Bio-protection involves selecting non-Saccharomyces yeasts belonging to different genera and species to induce negative interactions with indigenous microorganisms, thereby limiting their development and their impact on the matrix. Although the effectiveness of bio-protection in the winemaking industry has been reported in numerous journals, the underlying mechanisms are not yet well understood. The aim of this review is to examine the current state of the art of field trials and laboratory studies that demonstrate the effects of using yeasts for bio-protection, as well as the interaction mechanisms that may be responsible for these effects. It focuses on the yeast Metschnikowia pulcherrima, particularly recommended for the bio-protection of grape musts.

Metabolic Modeling of Wine Fermentation at Genome Scale

Wine fermentation is an ancient biotechnological process mediated by different microorganisms such as yeast and bacteria. Understanding of the metabolic and physiological phenomena taking place during this process can be now attained at a genome scale with the help of metabolic models. In this chapter, we present a detailed protocol for modeling wine fermentation using genome-scale metabolic models. In particular, we illustrate how metabolic fluxes can be computed, optimized and interpreted, for both yeast and bacteria under winemaking conditions. We also show how nutritional requirements can be determined and simulated using these models in relevant test cases. This chapter introduces fundamental concepts and practical steps for applying flux balance analysis in wine fermentation, and as such, it is intended for a broad microbiology audience as well as for practitioners in the metabolic modeling field.

Saccharomyces cerevisiae Gene Expression during Fermentation of Pinot Noir Wines at an Industrially Relevant Scale

This study characterized Saccharomyces cerevisiae RC212 gene expression during Pinot noir fermentation at pilot scale (150 liters) using industry-relevant conditions. The reported gene expression patterns of RC212 are generally similar to those observed under laboratory fermentation conditions but also contain gene expression signatures related to yeast-environment interactions found in a production setting (e.g., the presence of non-Saccharomyces microorganisms).

Saccharomyces cerevisiae metabolism produces ethanol and other compounds during the fermentation of grape must into wine. Thousands of genes change expression over the course of a wine fermentation, allowing S. cerevisiae to adapt to and dominate the fermentation environment. Investigations into these gene expression patterns previously revealed genes that underlie cellular adaptation to the grape must and wine environments, involving metabolic specialization and ethanol tolerance. However, the majority of studies detailing gene expression patterns have occurred in controlled environments that may not recapitulate the biological and chemical complexity of fermentations performed at production scale. Here, an analysis of the S. cerevisiae RC212 gene expression program is presented, drawing from 40 pilot-scale fermentations (150 liters) using Pinot noir grapes from 10 California vineyards across two vintages. A core gene expression program was observed across all fermentations irrespective of vintage, similar to that of laboratory fermentations, in addition to novel gene expression patterns likely related to the presence of non-Saccharomyces microorganisms and oxygen availability during fermentation. These gene expression patterns, both common and diverse, provide insight into Saccharomyces cerevisiae biology critical to fermentation outcomes under industry-relevant conditions.

IMPORTANCE This study characterized Saccharomyces cerevisiae RC212 gene expression during Pinot noir fermentation at pilot scale (150 liters) using industry-relevant conditions. The reported gene expression patterns of RC212 are generally similar to those observed under laboratory fermentation conditions but also contain gene expression signatures related to yeast-environment interactions found in a production setting (e.g., the presence of non-Saccharomyces microorganisms). Key genes and pathways highlighted by this work remain undercharacterized, indicating the need for further research to understand the roles of these genes and their impact on industrial wine fermentation outcomes.

The Impact of Oxygen at Various Stages of Vinification on the Chemical Composition and the Antioxidant and Sensory Properties of White and Red Wines

The purpose of this review was to collect and systematize information on the role and importance of oxygen in winemaking. Both the positive and negative effects of oxygen are presented and discussed throughout the text. The review characterizes the subsequent stages of the wine production process, during which oxygen comes into contact with fruits, must, and finally wine. The impact of oxygen on the growth and metabolism of yeast, on the activity of enzymes, and on the final quality of wine was presented. The discussion of the effect of oxygen presence on the taste, aroma, colour, and stability contains a detailed description of changes of volatile compounds, polyphenols, and other important components of wine that take place in the presence of oxygen in both white and red wines. New techniques based on the use of oxygen to obtain the desired sensory characteristics of wine were also presented.

RNA-seq based transcriptional analysis of Saccharomyces cerevisiae and Lachancea thermotolerans in mixed-culture fermentations under anaerobic conditions

Background

In wine fermentation starter cultures, the blending of non-Saccharomyces yeast with Saccharomyces cerevisiae to improve the complexity of wine has become common practice, but data regarding the impact of co-cultivation on yeast physiology and on genetic and metabolic regulation remain limited. Here we describe a transcriptomic analysis of mixed fermentations of Saccharomyces cerevisiae and Lachancea thermotolerans. The fermentations were carried out in carefully controlled environmental conditions in a bioreactor to reduce transcriptomic responses that would be due to factors other than the presence of the second species.

Results

The transcriptomic data revealed that both yeast species showed a clear response to the presence of the other. Affected genes primarily belonged to two groups: genes whose expression can be linked to the competition for certain trace elements such as copper and iron, as well as genes required for cell wall structure and integrity. Furthermore, the data revealed divergent transcriptional responses with regard to carbon metabolism in response to anoxic conditions.

Conclusions

The results suggest that the mixed fermentation created a more competitive and stressful environment for the two species than single strain fermentations independently from total biomass, i.e. competition between cells of the same species is less stressful, or may present a different set of challenges, than interspecies competition. The changes in cell wall and adhesion properties encoding genes suggest that the adjustment of physical contact between cells may play a direct role in the response to the presence of competing species.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5511-x) contains supplementary material, which is available to authorized users.

Study and Development of a Fluorescence Based Sensor System for Monitoring Oxygen in Wine Production: The WOW Project

The importance of oxygen in the winemaking process is widely known, as it affects the chemical aspects and therefore the organoleptic characteristics of the final product. Hence, it is evident the usefulness of a continuous and real-time measurements of the levels of oxygen in the various stages of the winemaking process, both for monitoring and for control. The WOW project (Deployment of WSAN technology for monitoring Oxygen in Wine products) has focused on the design and the development of an innovative device for monitoring the oxygen levels in wine. This system is based on the use of an optical fiber to measure the luminescent lifetime variation of a reference metal/porphyrin complex, which decays in presence of oxygen. The developed technology results in a high sensitivity and low cost sensor head that can be employed for measuring the dissolved oxygen levels at several points inside a wine fermentation or aging tank. This system can be complemented with dynamic modeling techniques to provide predictive behavior of the nutrient evolution in space and time given few sampled measuring points, for both process monitoring and control purposes. The experimental validation of the technology has been first performed in a controlled laboratory setup to attain calibration and study sensitivity with respect to different photo-luminescent compounds and alcoholic or non-alcoholic solutions, and then in an actual case study during a measurement campaign at a renown Italian winery.

The application of non-Saccharomyces yeast in fermentations with limited aeration as a strategy for the production of wine with reduced alcohol content

High alcohol concentrations reduce the complexity of wine sensory properties. In addition, health and economic drivers have the wine industry actively seeking technologies that facilitate the production of wines with lower alcohol content. One of the simplest approaches to achieve this aim would be the use of wine yeast strains which are less efficient at transforming grape sugars into ethanol, however commercially available wine yeasts produce very similar ethanol yields. Non-conventional yeast, in particular non-Saccharomyces species, have shown potential for producing wines with lower alcohol content. These yeasts are naturally present in the early stages of fermentation but in general are not capable of completing alcoholic fermentation. We have evaluated 48 non-Saccharomyces isolates to identify strains that, with limited aeration and in sequential inoculation regimes with S. cerevisiae, could be used for the production of wine with lower ethanol concentration. Two of these, Torulaspora delbrueckii AWRI1152 and Zygosaccharomyces bailii AWRI1578, enabled the production of wine with reduced ethanol concentration under limited aerobic conditions. Depending on the aeration regime T. delbrueckii AWRI1152 and Z. bailii AWRI1578 showed a reduction in ethanol concentration of 1.5% (v/v) and 2.0% (v/v) respectively, compared to the S. cerevisiae anaerobic control.