# Sustainable Vaporization of Wine Lees: From Waste to Value-Added Products
## 2 Wine Lees: Source and Physicochemical Composition
### Wine Lees Characterization  
Wine lees are defined according to the European Regulation EEC No. 337/979 as \"the sediment formed at the base of the deposit or barrel containing wine after fermentation, during storage or after performing authorized treatments to the product, as well as residues obtained from the filtration or centrifugation of said product\" [18]. One ton of grapes generates approximately 6% of wine lees, resulting annually in 2.96 million tons of yeast from the vinifraction of 49.4 million tons of grapes [18]. When alcoholic fermentation stops, a sludge-like material precipitates at the bottom of the wine tanks, consisting of living or dead yeast cells, yeast residues or other particles, which is called wine yeast [23,24]. Although it can be harmful to the environment if not managed properly, few studies have focused on yeast biomass [25,26]. Many studies have investigated the extraction of ethanol [27], tartaric acid [18], polyphenols [28,29,30,31], the production of culture media [32], as a source of beta-glucans [23] or mannoproteins [33], nutrient-rich fermentation supplements for the production of microbial oil [19] to support a sustainable outcome for wine lees [31]. Red wine yeast is found in larger quantities than white wine yeast and is known for its antioxidant and antimicrobial properties [34,35]. Rather than the total amount of phenolics, the phenolic content of wine lees has been associated with their antibacterial action [36]. Table 1 presents the composition of wine lees. Wine lees classification [8,31,40]:  
* first and second fermentation lees formed during alcoholic and malcolactic fermentations;
* aged wine lees formed during aging in wooden barrels;
* heavy lees (100 \(\upmu\)m-2 \(\upmu\)m, settling within 24 h) and light lees (<100 \(\upmu\)m, 1-24 \(\upmu\)m, in suspension at least 24 h after agitation). \begin{table}
\begin{tabular}{c c} \hline \hline
**Component** & **Value** \\ \hline Moisture (\% DM) & 87.0 \(\pm\) 1 [37]/4.21 [18] \\ Carbohydrates (\% DM) & 4.92 \(\pm\) 0.11 [37]/4.13 \(\pm\) 0.63 [31]/62.05 [38] \\ Proteins (\% DM) & 21.2 \(\pm\) 3.4 [37]/15.11 \(\pm\) 0.57 [31]/ \\  & 9.83 [38]/0.885 \(\pm\) 0.025 [18] \\ Lipids (\% DM) & 0.07 [37]/5.4 \(\pm\) 0.46 [31]/1.3 [38]/ \\  & 0.132 \(\pm\) 0.047 [18] \\ Dietary fibers (\% DM) & 20.1 \(\pm\) 3.0 [37]/21.5 \(\pm\) 0.35 [31] \\ Ash (\% DM) & 10.27 \(\pm\) 0.5 [37]/10.55 \(\pm\) 0.58 [31]/ \\  & 22.6 [38]/33.28 \(\pm\) 0.171 [18] \\  & 24.6 \(\pm\) 0.12 [31] \\ Hydroxycinnamic acid derivatives & 1.53 \(\pm\) 0.11 [39]/2.59 \(\pm\) 0.12 [39] \\  & 1.45 \(\pm\) 0.12 [39]/2.54 \(\pm\) 0.12 [39] \\ Catechins (mg catechin/100 g DM) & 15.09 \(\pm\) 1.36 [39]/30.24 \(\pm\) 1.71 [39] \\ \hline  & Calcium, Potassium, Magnesium, \\  & Phosphorus, Zinc, Iron [38] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The composition of wine lees. Several factors influence the characteristics of wine yeast, including environmental conditions, the region of origin, agronomic characteristics, grape variety, the winemaking process, and aging time [8]. Wine lees, a sludge material accumulated at the bottom of wine tanks after alcoholic fermentation, contain significant amounts of polysaccharides, proteins, lipids, and other organic molecules. They are a source of polyphenols with antioxidant activity, including anthocyanins and flavonoids [41]. The most abundant phenolic compounds were found in wine lees, with ellagic acid being the most abundant and quercetin being the most abundant flavonoid. The most representative concentration of anthocyanins was found in malvidin and malvidin-3-acetyl glucoside. Polyphenols, synthesized by plants in response to stress conditions, counteract free radicals and have beneficial health effects against oxidative stress, inflammatory activity, and neurodegenerative, cardiac, and metabolic diseases. They also have a protective effect on sight, promote the growth of probiotics, and modulate the gut microbiota, which can have beneficial effects on human health [41; 42].