## 2 Characterization of the Grape Cluster and Vinification Processes  
In grapevines, berries are attached to the stem to form a grape cluster, as shown in Figure 1. The berries consist of 85 to 92% of pulp, 6 to 12% of skin, and 2 to 5% of seed. The pulp consists of 65 to 85% of water, 12 to 25% of reducing sugars, 0.6 to 1.4% of organic acids, 0.25 to 0.5% of mineral substances, 0.05 to 0.1% of nitrogen compounds, and various water-soluble and fat-soluble vitamins [37]. Grape seeds are approximately 40% fiber, 16% lipids (oil), 11% protein, 7% phenolic compounds (mainly tannins), sugars, mineral salts, etc. In addition, grape seeds have a large amount of monomeric phenolic compounds, such as (+)-catechin, (-)-epicatechin, and (-)-epicatechin-3-O-gallate, and dimeric, trimeric, and tetrameric proyandias [7,38]. Grape skin is a source of anthocyanins and anthocyanin natural dyes and has antioxidant properties and antimutagenic activities [39], as cited by the author of [40]. Anthocyanins are mainly found in grape skin [40]. Anthocyanins can react with the flavonoids to produce more stable pigments, either directly or through different aldehydes. The color intensity depends on the anthocyanins' type, concentration, pH, degree of polymerization, etc. [41]. Flavan-3-ol is a significant group of phenolic compounds that contribute to the darkening process of grapes and wine. They also interact with anthocyanins to stabilize the color of red wine [42,43]. The stem is formed by the frame of the grape cluster that supports the fruit. The stem represents 3 to 7% of the grape cluster total [44]. It is a main residue produced during the winemaking process, and also has a high content of lignocellulosic material [45]. It contains a high concentration of tannins, which, if chewed, have a rough and asrtingent taste. Conveniently, the tannins present in the stem are not incorporated into the wine, and the grape should be destemmed before being pumped into the fermentation tanks. The main difference between white and red wine is that white wine is generally made from white grapes, but it can also be made from pink and red grapes. In this case, it is necessary to separate the liquid immediately from the solid phase, which contains the pigments responsible for the color. On the other hand, red wine is made only from red grapes. Figure 2 shows the winemaking process for white and red wine. Grapes are harvested, destemmed, and crushed. After that, the proper wine elaboration starts and 17% of the total weight of grapes used in the wine-making process are discarded (skins, seeds, stem, and lees, represented in step 3; see Figure 2) [46]. Figure 1: The grape cluster and berry morphology: **1**. stem; **2**. berries; **3**. seed; **4**. pulp; **5**. skin. Created by the authors using BioRender ([[https://biorender.com](https://biorender.com)]([https://biorender.com](https://biorender.com))). During maceration, the skin of red grapes is the source of extraction for anthocyanins and other phenolic compounds [47]. These phenolic compounds give the wine color, structure, body, and originality, as well as the claimed health properties [48]. In the production of red wine, maceration is followed by the inoculation of yeasts and alcoholic fermentation before the material is pressed and bottled. The inoculum consists of commercial yeasts produced in the laboratory that are selected for their fermentative behavior and the metabolites they produce. The inoculum helps the yeast perform more evenly and correctly, overcoming the deficiencies of the must and the needs of the yeast. The so-called malotactic fermentation follows the second fermentation. After that, there is an aging period before the final stages. Figure 2: Viniification process. By-products obtained during wine processing: (**a**) stem, (**b**) grape pomace, and (**c**) lees. * By-products’ percentages are indicated in reference to the mass of grapes used in the manufacture of wine.