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Showing posts from August, 2017

Encapsulated bacteria enhance MLF in stressful environments

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By Karien O'Kennedy
The aim of this study was to evaluate the effect of encapsulating a malolactic bacteria starter culture in two different gels to improve its activity and stability under stressful winemaking conditions. The two different encapsulation methods: a normal alginate gel as well as a silica-alginate gel, were also compared to a “free” version of the bacteria. The bacteria used in the trial was Lalvin VP 41 MBR from Lallemand. Bacteria was inoculated into de-alcoholised wine with adjusted concentrations of alcohol, pH, YAN and malic acid. Malolactic fermentation was also conducted at various temperatures ranging from 13 – 22°C.
Results The malolactic activity of the Si-Al capsules was significantly higher than the alginate capsules and the free bacteria, in high alcohol conditions. At 16% alcohol free bacteria decreased the malic acid concentration only 1% 72 hours after inoculation. The alginate capsules consumed 55% of the malic acid and the Si…

Pre-fermentation tannin addition enhances volatile thiol content of white wines

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By Karien O'Kennedy
The aim of this study was to examine the role of volatile thiols in the aroma Gewürztraminer wines, as well as the potential use of oenological grape tannin extracts as a source of thiol precursors. 500 kg of each of Gewürztraminer and Sauvignon blanc grapes were harvested in Trentino, Italy. Both grape varieties were fermented with VL3 (Laffort) and VIN 13 (Anchor Yeast) and both were treated with two types of tannins: one low in thiol precursors (Erbslöh) and one high in thiol precursors (Enartis). Tannin additions were done pre-fermentation and proper controls where no tannin addition was done were kept. In a second trial fermentations with VIN 13 only received tannins post-fermentation. Initial juice analysis: The two juices contained similar concentrations of the GSH-3MH precursor. The S. blanc juice had double the amount of Cys-3MH precursor than the Gewürztraminer juice. Both varieties had more GSH-3MH than Cys-3MH. Effect of tannin treatments: Tannin low did n…

Deficit irrigation and canopy management practices

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A field trial was carried out on 16 year-old Shiraz/R110 grapevines, between the 2011/12 and 2014/15 seasons in a semi-arid region. The objective was to determine the effect of different drip irrigation strategies and canopy manipulation combinations on vegetative growth, plant water potential, water usage, yield, overall wine quality and profitability.
Project layout The field experiment was done on a fine sandy loam soil about 25 km Southwest of Robertson;The soil was replenished back to field capacity by means of 3.5 L/h drippers once the total plant available water (PAW) within the root-zone (ca. 750 mm deep) depleted by respectively ca. 30%, ca. 60% and ca. 90%;For each irrigation strategy grapevines were hand pruned and canopies were either left unsuckered and sprawling, shoots vertical positioned (VSP) with suckering (two shoots per spur) or VSP without the suckering of water shoots;In addition, there was a further treatment…

Sauvignon blanc: The role of genotypic plasticity in cultivar typicity

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The aim of this project was to investigate how a grapevine responds, or adapts to environmental changes and how these changes affect the composition of grape berries and hence, wine quality. This experiment specifically looked at the effect of changes in light and temperature in the canopy.
Samples were collected over three vintages from a Sauvignon blanc vineyard in Elgin. Leaves were removed in the bunch zone, after flowering. Light and temperature in the bunch zone was characterized. Samples were then taken at five stages in berry development. Berry samples were analysed for sugars, organic acids, carotenoids, chlorophylls, volatiles and metabolites.
Results: Leaf removal increased light (including UV), but not temperature in the bunch zoneIncreased light exposure changed the metabolism of the berries (acclimation occurred)Plant response differed depending on what developmental stage it was at.Leaf removal did not affect berry weight and diameter or major sugars …