Wines & Vines

GRAPEGROWING to help "nourish" a wine. A subsequent racking often occurs in early July, and is in the absence of air. SO2 additions Timing of SO2 additions, and the quantity of SO2 are important stylistic considerations. Early addition increases the number of components that bind to subsequent additions of SO2. The addition of too much SO2 counters the wood flavors and limits oxidation reactions. D. Delteil compared red wines barrelstored on light lees for nine months and those racked several times to eliminate lees prior to barreling and stored for the same time period.4 Wines stored sur lie had a much lower perception of astringency and a greater integration of the phenolic elements. The sur lie wines also had a lower perception of oak character, resulting in a higher perception of fruit characters. Lees components such as polysaccharides and proteins are known to react with phenolic compounds, thus reducing astringency. Such reduction can cause an increase in the wine's volume or body. Lees contact is particularly effective at modifying wood tannin astringency by binding free ellagic tannins, thus lowering 78 p racti c al w i ne ry & v i n e yard AU G U ST 20 13 the proportion of active tannins. Sur lie storage can reduce the free ellagic acid by as much as 60%, while increasing the percentage of ellagic tannins bound by 24%.18,22 Addition products Proprietary products or treatment of lees with b-glucanases may aid in the increase of mannoproteins and glucans in a wine. The mannoproteins in commercial addition products may be different than those produced by yeast. Unlike many commercial products, yeast-derived mannoproteins generally have a mannose/glucose ratio of 1 to 1 and a relatively high protein content. Thus, it is likely that yeast mannoproteins will react differently in wine than some commercial products. Some winemakers age wines in the presence of lysated (broken) lees instead of fresh lees in order to reduce the time conserved on lees and to help avoid possible microbial and organoleptic risks. O. Fernandez et al. outlines the differences in wines produced with such treatments and fresh lees.6 Addition of enzymes to wines in the presence of lees may increase the glucose concentration providing a carbon source for micro organisms such as Brettanomyces.13 Summary impact of yeast lees Color and mouthfeel — High lees concentration can reduce color, as a function of adsorption onto the yeast cell surface and possibly as a result of anthocyanin destabilization from b-glucosidase activity. Additionally, lees adsorb oxygen that can limit the anthocyanin-tannin polymerization, impacting both color stability and resulting in an increase in dry tannin perception. Commercial mannoproteins may cause a greater color loss than yeast-derived mannoproteins. Wine aroma — Lees favor the synthesis of esters that can improve wine aromatics21 but also produce long chained alcohols and fatty acids, compounds that can detrimentally impact aroma.7 Aroma stabilization is dependent upon the hydrophobicity (ability to repel water molecules) of aroma compounds. The protein component of the mannoprotein fraction is important for overall aroma stabilization.15 Such interactions can modify the volatility and aromatic intensity of wines. When wine is aged on yeast lees with no fining, mannoproteins are present and fortify the existing aroma components. When wines are fined prior to élevage, mannoproteins can be removed and not be present to augment the existing aroma components. Additionally, when wines are cross‑flow filtered, eliminating a certain percentage of macromolecules, the loss of color intensity, aroma and flavor can occur.8,21 Yeast lees have been demonstrated to reduce the perception and concentration of 4-ethyl phenol and 4-ethyl guaiacol found in red wines as a function of Brett growth.13 This effect is significantly impacted by autolysis state of the yeast lees, pH, temperature, ethanol content and other constitutes adsorbed by the lees.20 Oak bouquet — Lees modify oaky aromas, due to their ability to bind with wood-derived compounds including vanillin, furfural and methyl-octalactones. Oxidative buffering capacity — Both lees and tannins act as reducing agents. During élevage, lees release certain highly reductive substances that can limit wood-induced oxygenation. Wines have a higher oxidation-reduction potential in barrels than in tanks. Inside a barrel, the potential diminishes from the wine surface to the lees. Stirring helps to raise this potential. This is a primary reason why wines stored in large-volume tanks are often not stored on lees. Such storage can cause

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