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56 WINES&VINES December 2016 WINEMAKING PRACTICAL WINERY & VINEYARD H igh-quality red wines generally require a period of aging in the bottle before they are ready for consumption. During this time, modifica- tions of sensory properties occur such as the decrease of astringency 1 and stabilization of color from purple-red to orange-red. Numerous appellations outside the United States impose a minimum period of bottle aging for high-quality red wines to achieve specific sensory attributes. However, wine aging implies a significant financial cost to each winery, so it is important to understand the timing, factors and mechanisms of astrin- gency and color changes during bottle aging. Astringency is a tactile sensation mainly elicited by the precipitation of salivary proteins that cause the mouth to feel dry. 2 Wine com- ponents responsible for astringency include phenolics such as proanthocyanidins (PAs) or wood tannins (ellagitannins and gallotannins) that react with salivary proteins, causing their complexation and subsequent precipitation on the mouth epithelium. 3 The color of red wine is due to anthocya- nins and derived copigments. While the main reactions involved in color stabilization are known, 4,5,6,7 the impact of reactions occurring during aging and involving PAs and anthocya- nins on the decrease of wine astringency are not well established. 1,8,9 In the past, this phe- nomenon was attributed to the formation of greater polymeric structures. 10 Unlike antho- cyanins, precise chemical analysis of changes in the tannin structures was not well known. Many of the complex reactions involving phenolics are affected by oxygen exposure to wine, and a moderate uptake of oxygen during aging can accelerate and/or trigger specific reactions influencing sensory proper- ties. 8,11,12,13,14 For this reason, aging of red wine in oak barrels is a widely used practice. In fact, the ingress of small amounts of oxy- gen through the wood and between wood staves results in many chemical reactions involving wine and wood phenolics, enhanc- ing the decrease of wine astringency and the stabilization of color. 15,16 This practice and bottle aging is expensive and implies a significant financial cost in the wine's bottle price. Micro-oxygenation (MOx) has been proposed to add a continuous flow of oxygen to a tank, simulating oxygen uptake occurring during wood aging. Besides the winemaking process, wine can be further exposed to oxygen during bottle aging, depending on oxygen perme- ability of the closure. Because of the ex- tremely low rate of oxygen ingress through a closure, this form of oxygen exposure is referred to as nano-oxygenation. 21 Oxygen transmission rates (OTR) of wine closures vary widely depending on closure type and strongly influence the evolution of white and red wines during bottle aging. 21,23,24,25,26,27 Additionally, the oxygen present at bottling, often referred to as total package oxygen (TPO), together with oxygen released from the closure upon insertion into the bottleneck also contrib- ute to oxygen exposure in the bottle. 28,29 Astringency evaluation In spite of the fact that oxygen exposure has been linked to many reactions by phenolics involved in the decrease of astringency, a clear correlation between chemical transformation of phenolics and their sensory properties has not been reported. This can be due to the fact that sensorial activity of wine tannins is not easy to predict because it is influenced by their chemical nature, quantity and the inner balance with other compounds present in wine. 2,30,31,32,33,34 Several analytical methods have been de- veloped to predict wine astringency by evaluat- ing the ability of wine to form insoluble complexes with human saliva. 35,36,37 Since 2010 the saliva precipitation index (SPI), based on the electrophoretic analysis of selected salivary proteins precipitated after reaction with wine polyphenols, has been utilized to objectively evaluate changes in astringency. Despite extensive research to evaluate the effect of micro- and nano-oxygenation on the evolution of phenolics in red wine, very few studies have evaluated the fate of micro-oxygen- ated wines after a long period of bottle aging. 21,22 No study has dealt with the impact of closure oxygen permeability on the saliva precipitation index (SPI) of red wine. 38 In this work, the SPI was utilized to objectively evaluate changes in astringency as a function of oxygen uptake before and after bottling. Sensory rating of as- tringency, polyphenolic composition and chro- matic characteristics also were evaluated. Micro-oxygenation trials Cantina del Taburno Winery produced two 2006 Aglianico red wines in agreement with standard procedures used for Aglianico del Taburno DOC wine. These wines were chosen because of their different pH levels. For both wines, two micro- oxygenation treatments were applied. Each wine was transferred from the initial tank into six 50 hL tanks (3 meters tall). Micro-oxygenation was performed on four tanks with a Microdue system. Oxygen was provided through a diffuser composed of a porous ceramic membrane. Two tanks were denoted as MO1, two others as MO2, and two tanks were control wines. After three months of MOx treatment, each wine was bottled in 750ml glass bottles flushed with 98% N 2 gas and sealed with a 44 mm natu- ral cork. Analyses were performed at bottling and after 42 months of aging in bottle. Nano-oxygenation trials Two red wines were used to study the influence of closure OTR on wine phenolic composition and astringency. Wine 1 was a blend of 40% Cabernet Franc, 40% Merlot and 20% Blaufrän- kisch. Wine 2 was a 100% Montepulciano. All bottles were sealed with Nomacorc co- extruded synthetic closures. Three distinct levels of oxygen exposure in the bottles were obtained by using closures with different oxygen ingress profiles: Select 300 (W1 low and W2 low ), Select 500 Oxygen's Impact on Red Wine Aging How red wine phenolics evolve in the bottle By Angelita Gambuti, Maurizio Ugliano, Alessandra Rinaldi and Luigi Moio