The use of the electronic nose in the wine industry is an emerging technology. Although electronic nose systems have been used in other industries as tools to monitor fruit maturity or quality control, the use of these systems for wine analysis has been debated. Many electronic nose sensor types exist, but have often been accused of primarily discriminating varying ethanol concentrations of wines as opposed to aroma and flavor volatiles. This study evaluated the use of a commercial conducting polymer electronic nose to evaluate wines while minimizing ethanol interference. The first study presented evaluated the discrimination ability of an electronic nose with use of an ethanol baseline prior to wine evaluation. This experiment also determined the optimal wine temperature for electronic nose analysis. A second study reviewed the ability of the electronic nose to discriminate Cabernet Sauvignon grape and wine volatiles based on a pre-fermentation cold soak treatment. The electronic nose was used to monitor volatile changes throughout a five day cold soak, and to discriminate differences in control versus cold soak wines. These results were compared with juice and wine analytical data, GC-MS evaluation of individual volatiles, and sensory analysis of the finished wines. It was found that discrimination of wines improved from 33% to 60% when using an ethanol baseline. Influence of the baseline was indicated by a drop in sensor response prior to wine evaluation. A 30°C sample temperature was chosen for wine analysis based on sensor response and adequate discrimination in canonical distributions. The electronic nose was found to discriminate grape volatiles in cold soak musts as shown in canonical distributions at a 95% significance level. PCA distributions of electronic nose data, chemistry data, and GC-MS data showed varying degrees of discrimination based on analysis. Electronic nose data often showed 100% of variation of samples accounted by PC1. Despite differences in treatment by ENose and analytical data, sensory results did not find a difference in control and cold soak wines. / Master of Science

Grape-derived aroma and flavor precursors exist partially as non-volatile, sugar-bound glycosides. Hydrolysis of these compounds may modify sensory attributes and potentially enhance wine quality. Cold soak (prefermentation skin contact) at two temperatures and alcohol content (%, v/v) at dejuicing were monitored to determine effects on Cabernet Sauvignon glycoside concentration. Total, phenolic-free, and red-free glycoside concentrations were estimated by the quantification of glycosyl-glucose. Cold soak (5 days at 10° C) increased total glycosides by 77%, red-free glycosides by 80%, and phenolic-free glycosides by 96%. Ambient soak (3 days at 20° C) enhanced color extraction, and increased total glycosides by 177%, red-free glycosides by 144%, and phenolic-free glycosides by 106%. Wines produced by early pressing (10% sugar) had 25% more total and red-free glycosides than late press (0.25% sugar). After post-fermentation malolactic fermentation, total glycosides were 14% lower and phenolic-free glycosides were 35% lower. In a second study, the activities of a-L-arabinofuranosidase, b-glucosidase, and a-L-rhamnoyranosidase were determined in model systems for thirty-two strains of yeasts belonging to the following genera: Aureobasidium, Candida, Cryptococcus, Hanseniaspora, Hansenula, Kloeckera, Metschnikowia, Pichia, Saccharomyces, Torulaspora, and Brettanomyces (10 strains); and seven bacteria (Leuconostoc oenos strains). Only one Saccharomyces strain exhibited -glucosidase activity, but several non-Saccharomyces yeast species had substantial production. Aureobasidium pullulans hydrolyzed a-L-arabinofuranoside, b-glucoside, and a-L-rhamnoyranoside. Eight Brettanomyces strains had -glucosidase activity. Location of enzyme activity was determined for those species with enzymatic activity. The majority of -glucosidase was located in the whole cell fraction (66%), followed by the permeabilized fraction (35%), and extracellular production (2%). Aureobasidium pullulans was also capable of hydrolyzing grape glycosides. / Master of Science

The consequences of pre-fermentation and post-fermentation extended maceration (EM) on colour, mouthfeel and phenolic composition were investigated in Pinot noir (2004), Grenache (2006) and Shiraz (2007) (Vitis vinifera L.) wines. Experimental wines were made using cold soak, post-fermentation EM, and standard fermentation treatments (C). Cold soak treatments included a 3-day cold soak at 10°C (CS), with an additional comparison of plunging effects for the 2004 wines (CSP). Post-fermentation extended maceration treatments were 1- or 3-weeks on skins in 2004 (PS1 and PS3 respectively), and 3-weeks in 2006 and 2007 (PS3). A variety of chemical and sensory test methods were used to determine changes in phenolic components and organoleptic properties between treatments of all 3 varietals as they aged in the bottle. Among other results, it was determined if wines made with a period of cold soak had increased colour intensity, and increased concentrations of monomeric anthocyanins and pigmented polymers compared to control wines. It was also determined if wines made with a period of post-fermentation EM had increased concentrations of the flavan-3-ols (+)-catechin and (−)-epicatechin, and tannin, decreased colour intensity and modified mouthfeel compared to the other wine treatments. A greater understanding of Australian red winemakers’ opinions on EM regimes and their use in Australian wineries was obtained by survey. Survey results confirmed that EM is used extensively in Australian wineries but that winemakers have poor understanding of the consequences of EM regimes for red wine properties. The survey confirmed that winemakers are concerned about the economic cost and logistic pressures associated with the use of EM regimes during vintage. Wines made using EM need to spend longer in fermentation vessels, which are in high demand during this time. Findings from this study provide winemakers with more information to consider before making decisions about their use of EM regimes. Survey findings showed more winemakers would use EM regimes if logistic and economic pressures did not apply. However, results suggest that even if winemakers did adopt EM practices, some may not achieve what they believe to be the outcome of these regimes, such as improved colour or mouthfeel properties. For instance, results showed that cold soaking did not make a difference to wine colour compared to conventional fermentation maceration. Even without cold soaking red must, winemakers may be able to achieve the same or very similar wine organoleptic characteristics at a reduced cost. Similarly, no significant effects of plunging during cold soak were observed. Post-fermentation EM visibly reduced wine colour intensity and imparted a browner hue to the wine compared to red wine that was pressed off skins upon reaching dryness. This EM regime is therefore unlikely to benefit winemakers who are seeking to produce highly coloured wines. However, prolonged maceration post-fermentation did increase the intensity of perceived bitterness and increased the concentration of wine flavan-3-ols and tannins. Winemakers may therefore influence the desired balance between the extraction of these wine phenolics (and the associated outcome for taste and mouthfeel properties) and economic considerations by varying the duration of maceration post-fermentation. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1362928 / Thesis (Ph.D.) - University of Adelaide, School of Agriculture, Food and Wine, 2009.