Inaugural Addresses (Viticulture and Oenology)

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    Industry-wide assessment and characterisation of problem fermentations
    (Stellenbosch : University of Stellenbosch, 2007-03) Malherbe, Sulette; Du Toit, M.; Bauer, Florian; University of Stellenbosch. Faculty of Agrisciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology.
    In order to remain competitive in the international wine market, wineries need to increase productivity and improve quality with the aid of available technologies. Problematic wine fermentations directly impact both productivity and the quality of wine and therefore, by reducing stuck and sluggish fermentations, less wine will be lost or downgraded. This requires early identification and classification of problem fermentations with the use of high throughput analytical tools and multivariate data analysis in order to take preventative measures. In this study, a non-directed, holistic approach was used to investigate the occurrence of problem fermentations in the South African wine industry. Data obtained with various analytical techniques was used for the purpose of multivariate data analysis. The use of high throughput analytical techniques such as Fourier transform infrared (FT-IR) spectroscopy proved extremely valuable as a fast screening method to monitor fermentation progress. Principal component analysis of the spectral fingerprints obtained with this technique indicated that all the fermentation problems occurred from the middle of fermentation onwards. In addition, successful discrimination between control and problem fermentations for different red and white cultivars was achieved. This demonstrates the feasibility of this type of methodology to investigate and monitor fermentation. Solid phase dynamic extraction (SPDE) headspace analysis was used to obtain a volatile fingerprint of the fermenting must samples. Similarly to FT-IR spectra, successful discrimination between problem and control fermentations was achieved with the use of PLS-discriminant analysis. Discrimination between red and white cultivars was achieved with headspace data. This excluded the data from tannin and colour compounds normally used for this discrimination. SPDE coupled to gas chromatography mass spectrometry (GC-MS) proved to be a novel and suitable analytical method for wine analysis, although further method development is required. A preliminary research and development strategy for evaluating FT-IR spectroscopy for quantification purposes in fermenting must was established. Although these calibration and validation results were preliminary, it was shown that the calibrations for fermenting must under South African conditions need urgent attention. In conclusion, this study illustrated the potential of using an alternative approach to investigate stuck and sluggish fermentation with definite prediction possibilities for future research endeavours.