Varietal differences between Shiraz and Cabernet sauvignon wines revealed by yeast metabolism

The main innovation in the VINIoT service is the joint use of two technologies that are currently used separately: vineyard monitoring using multispectral imaging and deployed terrain sensors. One part of the system is based on the development of artificial intelligence algorithms that are feed on the images of the multispectral camera and IoT sensors, high-level information on water stress, grape ripening status and the presence of diseases. In order to obtain algorithms to determine the state of ripening of the grapes and avoid losing information due to the diversity of the grape berries, it was decided to work along the first year 2020 at berry scale in the laboratory, during the second year at the cluster scale and on the last year at plot scale. Different varieties of white and red grapes were used; in the case of Galicia we worked with the white grape variety Treixadura and the red variety Mencía. During the 2020 and 2021 campaigns, multispectral images were taken in the visible and infrared range of: 1) sets of 100 grapes classifying them by means of densimetric baths, 2) individual bunches. The images taken with the laboratory analysis of the ripening stage were correlated. Technological maturity, pH, probable degree, malic acid content, tartaric acid content and parameters for assessing phenolic maturity, IPT, anthocyanin content were determined. It has been calculated for each single image the mean value of each spectral band (only taking into account the pixels of interest) and a correlation study of these values with laboratory data has been carried out. These studies are still provisional and it will be necessary to continue with them, jointly with the training of the machine learning algorithms. Processed data will allow to determine the sensitivity of the multispectral images and select bands of interest in maturation.

Originally, the role of the malolactic fermentation (MLF) was simply to improve the microbial stability of wine via biological deacidification. However, there is an accumulation of evidence to support the fact that lactic acid bacteria (LAB) also contribute positively to the taste and aroma of wine. Many different LAB enter into grape juice and wine from the surface of grape berries, cluster stems, vine leaves, soil and winery equipment. Due to the highly selective environment of juices and wine, only a few types of LAB are able to grow.

Controlling the speed of alcoholic (AF) and malolactic (MLF) fermentations in wine can be an important challenge for the production of certain short rotation wines for entry-level market segments. Immobilization techniques for Saccharomyces cerevisiae and Œnococcus œni, the microorganisms responsible for these fermentations, are widely studied for industrial applications. Indeed, these processes allow to accumulate biomass and thus to increase cell densities inducing high fermentation velocities. Recent works have shown the performance of MLF carried out with biofilms of O. œni, immobilized on various supports in a rich medium (MRSm: modified MRS broth with malic acid and fructose).

The selection, characterization, and recruitment of autochthonous yeast strains to drive the alcoholic fermentation process is a highly researched practice because it allows the differentiation of the organoleptic properties of wines, assuring process standardization, reducing fermentation times and improving the quality and safety of the final products [1, 2]. Sparkling wines are “special wines” obtained by secondary fermentation of the base wine. ​In the traditional method (Champenoise method), the re-fermentation takes place in the bottle after the addition to the base wine of the so-called tirage solution. This step, also known as prise de mousse, is followed by an aging period characterized by the release of compounds from the yeast cells that affect the organoleptic properties of the final product. The use of autochthonous yeasts as starter cultures for secondary fermentation is one of the recent innovations proposed to enhance and differentiate these wines’ sensory quality [3,4]. Apulia is the second Italian wine-producing region, and its productive chain is now going through a qualitative evolution by implementing the employment of innovative approaches to exalt the peculiar properties of regional wines.

Grapevine phenology has advanced across many regions, nationally and internationally, in recent decades under the influence of increasing temperatures, resulting in earlier
vintages (Jones and Davis, 2000, Petrie and Sadras, 2008, Tomasi et al., 2011, Webb et al., 2011. Earlier vintages have several ramifications for the wine industry. There are direct implications on quality, due to the fruit ripening during the hotter conditions of summer and early autumn, which then impacts grape composition and wine style (Sadras et al., 2013, Buttrose et al., 1971, Mira de Ordũna, 2010). There are also indirect implications where the fruit is perceived to ripen at a faster rate and the crop reach optimum maturity over a shorter period (Coulter et al., 2016).