# Comparative Proteomics of Two Flor Yeasts in Sparkling Wine Fermentation: First Approach
## 1 Introduction  
Sparkling wines have a high economic value, and their consumption and production have increased significantly in recent years, driven by various trends and changes in the market. Sparkling wines are a unique category of wine characterized by a significant amount of carbon dioxide, which produces its characterized effervescence when the bottle is uncorked. This effervescence results from an overpressure of CO2, which can be exogenous in the case of carbonated wines, or endogenous in the case of sparkling wines [1, 2, 3]. The latter can be produced with one (ancestral method) or two alcoholic fermentations. The second fermentation can be carried out in an isobaric tank (Charmat method) [4] or in a closed bottle (traditional or Champenoise method), which is the most widely used method [5]. This second fermentation takes place in bottles to which base wine and-tirage liqueur are added, consisting of sugar (approximately 20-24 g of sucrose/L), yeasts preadapted for the successful second fermentation (1 to 2 \(\times\) 10\({}^{6}\) cells/mL), and a riddling agent [6]. Therefore, the starter cultures selected for sparkling wine production must have several technological characteristics in addition to those suggested for yeast strains used in primary fermentation [7]. The use of selected autochthonous yeasts for second fermentation has recently been proposed to enhance the specific features of typical regional wines and to prevent fermentative problems [8; 9]. Autochthonous starter cultures represent a potentially important key to wine quality, due to their possible differential adaptation to specific environmental conditions and their prospective contribution to the differentiation of the organoleptic properties of final products [8; 9; 10; 11]. The work of [PERSON] et al. [11] testifies the existing interest in the characterization and selection of autochthonous yeasts to improve the diversification of sparkling wines.  
Flor yeasts are specialized strains of _Saccharomyces cerevisiae_ that form a biofilm on the surface of certain wines, such as sherry, during biological aging. Flor yeasts are innovative and ideal for the sparkling wine industry due to their resistance to high ethanol concentrations, surface adhesion properties that facilitate wine clarification, and the ability to provide a characteristic volatilome and odor profile [12]. Some proteomic studies on wine yeasts have been carried out in the second fermentation in-bottle because this is the level of expression closest to the final product in terms of organoleptic characteristics, and to understand the main biological processes under these conditions [13; 14; 15]. Previously, we explored the use of a flor yeast strain (_S. cerevisiae_ G1) in the second fermentation for sparkling wine production [12]. In this context, the first sparkling wine successfully produced with a flor yeast, named G1, was commercialized by the company Perez Barquero in collaboration with the University of Cordoba (Spain). In order to increase the diversity and applicability of flor yeast strains in sparkling wine production, we selected a new flor yeast (_S. cerevisiae_ N62) and carried out a first proteomic study using the G1 strain as a reference at mid-second fermentation. The main objective is to characterize (through qualitative and quantitative analysis) the proteomic profile of these two yeast strains, which is the closest level to the final product in terms of organoleptic characteristics.