Casassa et al.
Extended maceration and ethanol concentration
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Effect of extended maceration and ethanol concentration on the extraction and evolution of phenolics, colour components and sensory attributes of Merlot wines L. FEDERICO CASASSA, C.W. BEAVER, M.S. MIRELES and J.F. HARBERTSON School of Food Science. Irrigated Agricultural Research and Extension Center, Washington State University (WSU), Prosser, WA 99350, USA Correspondence author: Dr James F. Harbertson, email
[email protected] Abstract Background and Aims: Anecdotal evidence suggests that there may be a synergistic effect of ethanol (EtOH) and prolonged skin contact on the extraction of certain phenolics that may negatively impact wine sensory properties. The combined effect of extended maceration (EM) and EtOH concentration was studied during winemaking and bottle ageing. Methods and Results: The evolution of phenolics and colour components was followed for up to 1 year of bottle ageing. Harvest skins and seeds and those obtained from the pomace after maceration were also analysed. Sensory attributes were studied by Quantitative Flavour Profiling. The relationship between the chemical and sensory data was explored with Partial Least Square Regression. EtOH concentration differing by 1.2% v/v had no effect on tannin and anthocyanin extraction, colour, tannin mean degree of polymerisation, polymeric pigment formation and recovery of anthocyanins and tannins in the pomace after maceration. The maceration length defined the chemical and sensory profile of the wines. The tannin content of wines produced with EM was mainly derived from seed tannins, whereas control wines had a balanced proportion of seed and skin tannins. The anthocyanin concentration was lower in EM wines, whereas polymeric pigments and tannins were predictors of astringency. In control wines, perceived red colour was associated with anthocyanins, vitisins, a* (red component), and small polymeric pigments. Significance of the Study: Evidence of the nature and interrelation of the chemical and sensory composition of wines obtained with EM is provided. Major chemical features responsible for the sensory properties of wines produced by two contrasting skin contact regimes are identified. Keywords: colour, ethanol, extended maceration, phenolic, sensory analysis
Introduction Extended maceration (EM) prolongs skin and seed contact after the must has fermented to dryness (Sacchi et al. 2005). This practice has gathered attention because of its potential to enhance phenolic extraction (Auw et al. 1996, Canals et al. 2005), stabilise wine colour (Auw et al. 1996, Puertas et al. 2008) and alter mouthfeel properties (Schmidt and Noble 1983, Joscelyne 2009). Because of the anecdotal belief that full-bodied wines can be obtained only from fruit that undergoes extended ripening, there is a concern about the synergistic effect of ethanol (EtOH), resulting from high °Brix fruit, and prolonged skin contact on the extraction of certain phenolics that may impart negative sensory properties. Therefore, it is of interest to document the chemical and sensory characteristics derived from the interaction between EM and EtOH concentration during winemaking. Fruit maturity plays a critical role in anthocyanin and tannin extraction, polymeric pigments’ formation and modulation of astringency (Canals et al. 2005, del Llaudy et al. 2008, Harbertson et al. 2009). Anthocyanin extractability into wine progressively increased from ~14°Brix to 26.7°Brix (Canals et al. 2005, Fournand et al. 2006, del Llaudy et al. 2008). Conversely, tannin extraction into wine, particularly from seeds, has been doi: 10.1111/ajgw.12009 © 2013 Australian Society of Viticulture and Oenology Inc.
reported to decrease with ripening (del Llaudy et al. 2008, Bautista-Ortín et al. 2012). Elevated EtOH concentration, however, resulting from high °Brix fruit may increase the intrinsically lower extractability of seed tannins, reportedly because of the dissolutive effect of EtOH on the lipidic outer coat of the seeds (Glories and Saucier 2000). In turn, enhanced tannin extraction from seeds during maceration increased perceived astringency of wine (Harbertson et al. 2009). Seed tannins are compartmentalised in thin-walled parenchyma cells located between the cuticle and the inner lignified layers of the seeds (Thorngate and Singleton 1994, Adams 2006). Seed tannins are composed by catechin, epicatechin and epicatechin-3-O-gallate (Prieur et al. 1994), which are present mainly as monomers, but oligomers and polymers also exist. Moreover, the mean degree of polymerisation (mDP) of seed tannins is lower than that of skin tannins (Prieur et al. 1994, Souquet et al. 1996). Generally, longer maceration times increase the contribution of seed tannins (Vrhovsek et al. 2002, del Llaudy et al. 2008). In model wines, seed tannins contributed 90% of the wine tannin content after 3 weeks of maceration (González-Manzano et al. 2004) and similar results were found on an industrial scale (Harbertson et al. 2009). Conflicting results however, have been reported for the effect of variable
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Extended maceration and ethanol concentration
EtOH concentration on seed extraction. In model wines, Singleton and Draper (1964) found that 14% EtOH extended the lag phase of tannin extraction compared with that of 11% EtOH, which was attributed to a tissue toughening effect by EtOH. Yet, at longer contact times, higher EtOH increased extraction (Singleton and Draper 1964). In another report, an EtOH content ranging from 0 to 10% v/v had a marginal effect on the extraction of catechin, epicatechin and proanthocyanidins dimers B1, B2 and B4 over a 96-h extraction period (Oszmianski et al. 1986) although no further analysis was done beyond this point. Skin proanthocyanidins are located in the vacuoles of thickwalled hypodermal cells (Adams 2006), with those associated with cell wall polysaccharides having a higher degree of polymerisation (Gagné et al. 2006). Extraction of monomeric and oligomeric tannins from skins occurs early during maceration (Koyama et al. 2007). Relative to seeds, however, the extraction pattern of skin tannins of high molecular weight follow an erratic behaviour because of the subsequent non-covalent rebinding by cell wall material (Bindon et al. 2010, Hanlin et al. 2010). As in seeds, the effect of EtOH concentration on tannin extraction from skins has proven to be inconsistent. In model wines, increasing the EtOH concentration from 0 to 13% v/v increased extraction of skin tannins in unripe fruit (Canals et al. 2005), but no differences were found when comparing extraction solutions at 11 and 13% v/v EtOH applied to fruit at technological maturity (Gambuti et al. 2009). Although the loss of anthocyanins during EM is well documented (Scudamore-Smith et al. 1990, Kelebek et al. 2006), the effect of variable EtOH concentration on anthocyanin extraction remains unclear. In addition to their direct role on wine colour, the presence of anthocyanins during maceration increases the solubility and retention of tannins via the formation of polymeric pigments (Kantz and Singleton 1991, Singleton and Trousdale 1992). Polymeric pigments encompass a heterogeneous array of compounds, including pigmented tannins and acetaldehyde cross-linked products (Somers 1971, Kennedy and Hayasaka 2004). These pigments differ from intact anthocyanins in that they are partially resistant to bisulfite bleaching and more resilient to pH change (Somers and Evans 1977). There appears to be, however, a complex relationship between tannin content, anthocyanin extraction (or loss) and polymeric pigment formation during maceration. Quantitative Flavour Profiling (QFP) is a sensory technique where trained panellists evaluate a list of descriptive terms previously selected by a group of experienced tasters (Stampanoni 1993). The QFP approach has the advantage over Quantitative Descriptive Analysis in that the panellists do not have any preconceived ideas because they are not involved in the development of the descriptors (Stampanoni 1994). Here we report the combined effect of EM and EtOH concentration on the extraction and evolution of anthocyanins, tannins and colour components during and post-maceration, and up to 1 year of bottle ageing. Sensory properties were studied with QFP.
Materials and methods Winemaking Merlot grapes (clone 3) were harvested on 23 September 2010 from Goose Ridge vineyard in Paterson, WA, USA, which is located in the American Viticultural Area-designated Columbia Valley. Two adjacent vineyard blocks differing by ~1°Brix, to target two levels of final EtOH concentration, were harvested separately into four 500-kg capacity bins. Two skin contact treatments were established in triplicate for each block: control
Australian Journal of Grape and Wine Research 19, 25–39, 2013
wines, with a 10-day skin contact period, and extended maceration wines (EM) with a 30-day skin contact period, affording 12 wines. The fruit was crushed and destemmed using a Mearelli crusher (Cinquemiglia, Città di Castello, Italy); 50 mg/L of sulfur dioxide (SO2) was added. The must was fermented in 300 L stainless steel jacketed fermentors with mobile lids (Ghidi Metalli, Buggianao, Italy) filled with ~120 kg of must. Musts were inoculated 4 h after crushing with dry yeast (Lalvin EC-1118, Lallemand, Montreal, Canada) at a rate of 250 mg/L. Malolactic bacteria (Lalvin VP41, Lallemand) were added 48 h after yeast inoculation at a rate of 10 mg/L. Diammonium phosphate was added to raise the yeast assimilable nitrogen to 225 mg/L prior to fermentation. Sugar consumption during fermentation was monitored with a handheld densitometer (DMA 35N, Anton Paar, Graz, Austria) and tank temperature was maintained at 26 ⫾ 2°C using a web-based fermentation system (TankNet, Acrolon Technologies, Sonoma, CA, USA). Reducing sugar was measured by the Rebelein method (Iland et al. 2004). Cap management consisted of a whole-volume tank pump-over followed by a 2-min punch down twice a day during fermentation. Alcoholic fermentation was completed (reducing sugars
