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Showing posts from January, 2019

Determining factors that may reduce or shorten the productive lifespan of rootstock mother plantations

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Researcher: Francois Halleen

New Winetech funded project 2019: The aim of this project is to identify factors that may reduce or shorten the productive lifespan of rootstock mother blocks. In this study, physical, physiological and pathogenic detail will be considered on the same mother material. This approach has not been followed before and may provide answers that are hitherto unknown.
Attempts have been made in the past to link physiological and physical dimensions of graft material to performance of grafted vines. Field observations indicated that poor performance could be rootstock, terroir and/or cultivation related, without the conclusive involvement of pathogens. Accumulation of pathogen infections inside rootstock mother vines will occur over time through pruning wounds. Currently the risks associated with ageing rootstock mother blocks are unknown as most of these infected rootstock canes will visually appear as healthy. In practice it is unknown at what age mother blocks r…

The effect of must sterol content on alcoholic fermentation

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By Karien O'Kennedy
The aim of the study was to investigate the phytosterol content of grape solids that form part of grape must turbidity and how it affects yeast cell viability and fermentation rate.
Project layout: Solid particles from seven different musts were obtained: two red, two rosé and three white musts.Fermentations were conducted in synthetic grape must with 250 g/L sugar (equal concentrations of glucose and fructose) and a YAN of 425 mg/L (72% amino acids and 28% ammoniacal nitrogen).A preliminary experiment was set up with a negative control (synthetic must with no sterol or solid particle addition), as well as synthetic must with 1.5, 3.0, and 6.0 mg/L synthetic β-sitosterol respectively.The first set of experiments was set up with a negative control (synthetic must with no sterol or solid particle addition), a positive control (synthetic must with 1mg/L synthetic β-sitosterol), and synthetic must with solid particles from the different real grape musts with a final …

UV-C treatment of grape must for the inactivation of microorganisms

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By Karien O'Kennedy
The aim of the study was to investigate the efficacy of UV-C treatment of grape musts for inactivation of wine-related microorganisms. In addition the effect on the physicochemical, chemical and sensory characteristics of wine was investigated, as well as the mutagenic potential of UV-C treated grape must.
Project layout: Riesling, Müller-Thurgau, Pinot blanc and Pinot noir were harvested during 2014, 2015 and 2016 in the Rheinpfalz.Musts were clarified to below 50 NTU and pasteurized.A portion of Riesling was not pasteurized and further subdivided into clarified (below 50 NTU) and a turbid fraction.Musts were inoculated with Saccharomyces cerevisiae, Metschnikowia pulcherrima, Pichia fermentans, Candida sp., Hanseniaspora uvarum and Schizosaccharomyces pombe at 106 CFU/mL.Grape musts were subjected to different amounts of UV-C treatment at 10°C.Physicochemical determination, oxygen measurement and mutagenicity measurements were done.Wines were made from the fre…