# An Overview of CRISPR-Based Technologies in Wine Yeasts to Improve Wine Flavor and Safety
## 1 Introduction  
Wine aroma and flavor are the major attributes determining the preferences of wine consumers [1]. When drinking wine, in the mouth, the wine warms, making aromatic molecules escape up the retronasal passage to reach the olfactory area, activating receptors in the olfactory epithelium [2]. At the same time, the taste buds, about 10,000 of them distributed all over the tongue and in the inside of the mouth, sensitive to the six basic \"tastes\"--sourcomes or acidity, sweetness, bitterness, saltiness, the \"savory\" umami and the \"fat-taste\"--are excited [3]. Wine also contains components that can influence the inside of the mouth: (i) tannins that taste bitter and let as perceived astringency; (ii) alcohol, which affects our nervous system, in wines that are particularly alcoholic, acidic, and with a high concentration of phenolics, can leave a \"hot\" sensation on the palate after tasting; and (iii) glassy carbon dioxide, which has a physical, tactile effect, varying from a gentle pickle to an uncomfortably overwhelming froth, which, due to its perceived acidity, also makes the wine taste fresher [4]. At the same time, a sensory experience, which we call \"flavor,\" occurs, and it can be described as \"(...) a mingled experience based on human judgment, built on personal differences in perception thresholds\" [5]. Yeasts possess a major role in wine chemical composition, not only because they produce enzymes that convert neutral grape metabolites into flavor active compounds but also because they produce secondary metabolites during fermentation and can extract flavor components from grape solids and by cell autolytic degradation [6]. These reactions vary with the yeast species and strains contributing to the fermentation. Therefore, one of thetools that can assist winemakers to produce wines with specific flavor profiles is the choice of the yeast or yeast culture strains to conduct fermentation [5]. The \"prima donna\" yeast will be the one that efficiently completes the conversion of grape sugars to ethanol, carbon dioxide, and sensorially important metabolites, without the development of off-flavors [7]. Another important characteristic consists of the modification of grape-derived constituents (glyco- and cysteine-conjugates), which will enhance the wines' varietal character [7]. Moreover, the production of a \"safer wine\" is also one of the concerns in the wine industry. Winemakers feel the need to use yeast strains with peculiar features, such as low production of undesirable metabolites and already named \"harmful compounds\" such as SO\({}_{2}\), acetaldehyde, biogenic amines (BAs), and ethyl carbamate (EC), among others [8; 9]. Beginning in the 1990s, classical strain improvement methods focused on successive stages of mutagenesis and selection [10] have been used to obtain yeast starters for wine-making. These methods are extensive and time-consuming, requiring the screening of a significant number of isolates [11]. However, an evolution occurred, and strains' optimization, aiming to achieve mutants with the desired phenotype, by serial or the continuous culturing of a particular yeast for many generations under a selective pressure environment, began to be the more promising technique [12]. The supremacy of this last approach concerning the optimization of wine yeast is characterized by the creation of strains with increased sulfite tolerance and glycerol accumulation [13], strains with improved resistance to acetic acid and even acetic acid consumption [14], as well as enhanced viability and antioxidant production [15], among other interesting enological traits.