# Sustainable Vaporization of Wine Lees: From Waste to Value-Added Products
## 2 Wine Lees: Source and Physicochemical Composition
### Bioactive Compounds  
Red wine lees are a significant source of phenolic compounds [7], which contain flavonoids, a group with aromatic rings that have antioxidant properties, inhibiting free radicals in the human organism due to their oxidation-reduction capacity [31; 44]. The phenolic content of dried WL is high, with gallic acid, caffeic acid, myricetin, quercetin, syrginic acid, and p-coumaric acid being major phenolic compounds [34]. Extraction is a critical stage in the recovery of phenolic compounds; hence, the extraction parameters must be carefully regulated to produce extracts rich in bioactive compounds [8]. The extraction of bioactive compounds from wine yeast can be achieved using various methods to ensure optimal yields. However, most studies focus on alcoholic fermentation yeast, and only a small portion on malolactic fermentation. The increasing demand for more effective recovery methods led to the development of new unconventional treatments. By lowering extraction time, process temperature, and solvent consumption, these novel techniques can enhance extraction efficiency while consuming less energy [22]. In principle, binary mixtures (e.g., ethanol-water) are used, and the most used extraction method is ultrasound method extract [45]. Other extraction methods used are microwave, conventional, membranes, enzymatic, or supercritical. The potential of wine yeasts as a source of bioactive compounds is highlighted, with the need for further research exploring alternative extraction technologies and combining methods [29; 46]. As an environmentally friendly substitute for traditional solvents, natural deep eutectic solvents (NADESs) were studied by [PERSON] et al. [47]. Choline chloride: malic acid is the most promising of the NADES studied, and it has been shown to be successful in extracting anthocyanins from wine lees when compared to traditional solvents [47]. [PERSON] et al. investigated the extraction of polyphenols from wine lees using membrane technology. Ultrafiltration (UF) and nanofiltration (NF) membranes are used in a sequential filtration process under various operating conditions. According to the statistics, UF had a rejection rate of 54% and NF had a 90% rate [30]. Water was used as the solvent in a green liquid extraction process to recover phenolic acids, flavonoids, and related chemicals from wine lees. After microfiltering the resultant extract solution to eliminate microparticles, it underwent ultrafiltration (UF) employing membranes with molecular weight cut-offs (MWCOs) of 30 kDa and 5 kDa [48]. [PERSON] et al. investigated the oxidation of phenolic compounds using the flavonoid model (it provides a simpler matrix for understanding chemical changes during oxidation), and all wine lees samples showed bioactivities, the oxidation treatment not having a significant impact on antioxidant activity [49]. From the anthocyanins group, malvidin-3-O-glucoside and malvidin-3-(6''-p-couramygllucoside) were detected in higher concentrations. The main hydroxycinnamic acids identified in lees are tartaric, ferulic, p-couramic, and caffeic acids [31].