Effect of Skin Contact Before and During Alcoholic Fermentation on the Chemical and Sensory Profile of South African Chenin Blanc White Wines

The volatile and phenolic composition of Chenin blanc wines made with different skin contact treatmentswas studied. One batch of grapes was used to make a dry white wine according to two different treatments,namely pre-fermentative skin contact and complete fermentation on the skins. A white wine fermentedwithout any skin contact was used as control. Fermentation on the skins and skin contact beforefermentation led to significantly lower levels of terpenes, esters, acids and thiols, and the highest significantlevels of alcohols and phenolic compounds. However, this effect was less pronounced in wines with skincontact before fermentation. Sensory analysis of all the experimental wines was also performed. The resultsshowed a significant shift from the sensory attributes of fresh and tropical fruits of the control Cheninblanc wines towards riper fruit notes in the skin contact treatments. This observation was correlated withthe length of the skin contact period. Possible reasons to explain the results observed in this study arediscussed

Detection and Quantification of Grapevine Bunch Rot Using Functional Data Analysis and Canonical Variate Analysis Biplots of Infrared Spectral Data

Grapevine bunch rot assessment has economic significance to wineries. Industrial working conditionsrequire rapid assessment methods to meet the time constraints typically associated with grape intakeat large wineries. Naturally rot-affected and healthy white wine grape bunches were collected overfive vintages (2013 to 2016, 2020). Spectral data of 382 grape must samples were acquired using threedifferent, but same-type attenuated total reflection mid-infrared (ATR-MIR) ALPHA spectrometers. Thepractical industrial problem of wavenumber shifts collected with different spectrometers was overcome byapplying functional data analysis (FDA). FDA improved the data quality and boosted data mining effortsin the sample set. Canonical variate analysis (CVA) biplots were employed to visualise the detection andquantification of rot. When adding 90 % alpha-bags to CVA biplots minimal overlap between rot-affected(Yes) and healthy (No) samples was observed. Several bands were observed in the region 1734 cm-1 to 1722cm-1 which correlated with the separation between rot-affected and healthy grape musts. These bandsconnect to the C=O stretching of the functional groups of carboxylic acids. In addition, wavenumber 1041cm-1, presenting the functional group of ethanol, contributed to the separation between categories (severity% range). ATR-MIR could provide a sustainable alternative for rapid and automated rot assessment.However, qualitative severity quantification of rot was limited to only discriminating between healthy andsevere rot (> 40 %). This study is novel in applying FDA to correct wavenumber shifts in ATR-MIR spectraldata. Furthermore, visualisation of the viticultural data set using CVA biplots is a novel application of thistechnique

Winery on-site assessment of grapevine bunch rot: In pursuit of sustainable practices: Winery On-site Assessment of Grapevine Bunch Rot

Producer wineries are responsible for the processing of 75% of South Africa’s annual wine grape production. Characteristic to producer wineries is the processing of large volumes of wine grapes, thus incorporating enormous variability in grape quality, which include the presence of grapevine bunch rots. Grapevine bunch rots are detrimental to grape and wine quality. This review begins with the authors bringing background on the industrial situation at producer wineries. A section follows where the economic effect of rot infection on wine production is written about. Two principal reasons why rot infections are inevitably part of grape production are discussed. Challenges for producer wineries in terms of accurate rot assessment is set out. The last part of the review focusses on the quest for sustainable assessment of grapevine bunch rot infections under industrial conditions. Infrared spectroscopy (IR) could provide a sustainable option for objective assessment of rot infection on-site at producer wineries. However, even with the availability of plenty of spectroscopic methods, as well as demonstrated potential of IR spectroscopy for rapid assessment of grapevine bunch rot infections, these methods are yet to be applied routinely under industrial conditions