# Recovery of Polyphenols from Agri-Food By-Products: The Olive Oil and Winery Industries Cases
## 3 Polyphenols from Wine Production Wastes: Source and Applications
The main wine processing schemes and the main streams of interest as a source of polyphenols are described in Figure 4.  
As depicted in Figure 4, the main waste streams of interest for potential polyphenol recovery are grape pomace, clusters or grape stems, wine lees, and wine processing wastewater. Grape pomace is the residue that originated during the pressing of the grapes to produce must. It is constituted by the skins and seeds of the grapes. During the vinicification process, a large amount of grape pomace is generated. Nowadays, 9 million tons of this organic waste are produced per year in the world, which constitutes, on average, 20% of the total grapes used for wine production [31]. This residue constitutes an important source of phenolic compounds, mainly anthocyanins, flavonoids, phenolic acids, and stilbenes [8]. Grape pomace is used for the production of citric acid, methanol, ethanol, and xanthan through fermentation, and it is also employed for the production of energy [7; 31]. Several studies have reported a high antioxidant activity of this by-product, suggesting that grape pomace is an interesting source of natural antioxidants [31]. Clusters or grape stems constitute a residue of the wine industry that is used as a source of astringent compounds, represented mainly by proanthocyanidins. This residue is eliminated before the vinicification step to prevent an excessive wine astringency or a negative effect on organoleptic characteristics [31]. Figure 4: Wine processing schemes (adapted from [33]). Reproduced with permission from [PERSON], et al. Waste Management; published by Elsevier, 2011. Wine lees are generated during the fermentation and maturation processes of the wine. They are composed of solid and liquid fractions. The solid fraction contains the deposits formed at the bottom of the tanks, which mainly consist of yeasts and bacteria, carbohydrates, phenolic compounds, lignin, proteins, metals, inorganic salts, salts of organic acids (e.g., tartrates), and grape residues. On the other hand, the liquid phase mainly consists of the spent fermentation broth; therefore, it is rich in ethanol and organic acids. Besides, lactic acid from malotactic fermentation and acetic acid may also be present in significant amounts [27]. Finally, the vinasses are the residual liquid fraction of the wine lees distillation process, which is carried out to recover ethanol and produce distilled beverages [27]. Wine processing wastewater is a residue generated during different stages of wine production: fermentation, storage, and maturation (washing tanks and containers), clarification (wastewater generated by filtration), decanting, and bottling (spills and cleaning of containers and bottles) [34]. Wine production generates large amounts of wastewater; between 0.5-14 L per liter of wine produced. They are mainly acidic, phytotoxic with a high biological oxygen demand (BOD) and a relatively high concentration of phenols [34; 35]. The mean values of chemical oxygen demand (COD) and BOD are 11.886 mg L\({}^{-1}\) and 6.570 mg L\({}^{-1}\), respectively [34; 36].