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Using in-canopy misters to mitigate the negative effects of heatwaves on grapevines

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By Lucinda Heyns
This study aimed to determine whether in-canopy misters could provide effective cooling in vineyards in order to mitigate the negative effects of heatwaves.
Project layout: To address the challenge, the study was conducted in the Riverland and Adelaide regions in Australia on Sauvignon blanc and Cabernet Sauvignon. The study lasted two seasons, namely 2016-2017 and 2017-2018. Grapevine canopies were cooled using the following water-based, evaporative treatments: Fine mist application in the canopy (ICM) when temperatures exceeded 35 °CUnder canopy sprinklers (UCS) during warm nights preceding heatwavesSupplemental drip irrigation (SI) during warm nights preceding heatwaves
Results: In all treatments, canopy temperatures were 5°C cooler than ambient temperature.During heatwaves, the SI treatment with additional irrigation maintained under vine temperatures of 2°C lower than the control while midrow temperatures were 7°C lower than the control.In most treatments, cooling re…

Antifungal activity of new bioproduct obtained from grape seeds on Botrytis

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By Lucinda Heyns
This study tested the antifungal properties of a new bioproduct obtained from proanthocyanidins extracted from grape seeds.
Project layout: The bioproduct was extracted from grape seeds of the Fetească neagră variety.Grape seeds were extracted, dried, milled and defatted, in order to extract the phenolic compounds.The extraction of polymeric proanthocyanidins was done with ethanol.Antifungal activity of the bioproduct was determined in vitro by mycelial growth and spore germination inhibition.Assays were performed on three strains of Botrytis cinerea.
Results: The product proved to have effective antifungal properties by inhibiting spore germination. This means that this bioproduct has the potential to be used as a natural fungicide for biological control of Botrytis. This is only a laboratory study. Before a commercial product can be made available, field trials will be need to be done to optimise application methods and to test the persistence of the agents in the fie…

Efficacy of clarifying agents in the removal of pesticide residues in red wine

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By Karien O'Kennedy

The aim of the study was to evaluate different clarifying agents for their efficacy to remove pesticide residues from red wine. Residues have been detected in both white and red wines due to pesticide use in viticulture for crop protection.

Experimental layout:

Certified reference standards of 23 pesticides were obtained and two mixtures prepared, one containing all 23 pesticides and one only nine pesticides, representing nine main chemical groups. 75 ml samples of red wine (Greek cultivar: Agiorgitiko) were treated with the pesticide mixtures as well as with single solutions of the different pesticides. Seven fining agents were used for the trial: food grade activated carbon, bentonite, PVPP, gelatin, egg white, isinglass and casein. With the exception of the activated carbon all fining agents were obtained from Laffort.Two different dosages of each fining agent were used, the minimum and maximum dosages as suggested for winemaking. Pesticide residues were deter…

Survival of Brettanomyces in grape pomace

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By Karien O'Kennedy

The aim of the study was to determine if Brettanomyces can survive in grape pomace under conditions typically found in vineyards and as a result serve as a source of contamination for future harvests.

Experimental layout of short term incubation studies

A Syrah wine was produced and the free run wine separated from the un-pressed pomace. The pomace was placed in sterile polypropylene bottles of which half of the pomace containing bottles were autoclaved. The bottles were inoculated with one of three different strains of Brettanomyces and kept at 21°C for seven days before incubation at four different temperatures: 21°C, 10°C, 0°C and -18°C. At various stages bottles were removed from the given storage temperature and Brett enrichment medium added before further incubation at 21°C for 18, 168 or 720 hours, in order to evaluate the culturability of Brett. 
Experimental layout of long term experimental studies

In year one pomace from Syrah wine at two different alcoho…

Use of mushroom leachate for vine foliar nutrient application

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By Lucinda Heyns
The aim of this research was to study whether the nitrogen rich waste water from mushroom production can be used as a biostimulant in vineyards and whether it has an effect on grape volatile compounds.
Project layout: The study was carried out over two seasons on a Tempranillo vineyard in Spain.The leachate was applied at veraison and one week after veraison as a foliar spray.Two types of leachate was used: Mushroom water (MW) – normal leachate water extract; Treated mushroom water (TMW) – leachate extract with added liquid concentrate containing microorganisms that can fix nitrogen.Basic analysis were done and volatile compounds were measured.
Results: Treatments had no effect on pH, total acidity, YAN or potassium levels in the must.In the first season the TMW treatment had no effect on grape volatile compounds while a few volatile compounds were significantly reduced in the MW treatment.In the second season, where YAN levels were lower, the MW treatment increased th…

Reduction of Brettanomyces bruxellensis populations from oak barrel staves using steam

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By Karien O'Kennedy
The aim of the study was to determine the impact of oak species, barrels toasting level, location of staves in barrels and barrel age on Brettanomyces recovery, before and after the application of steam. Experimental layout: New 16 L barrels from American oak and French oak with light and heavy toasting levels were used. Each barrel had 24 staves with 20 mm thick midpoints. Four three year old 225 L barrels were obtained from a commercial winery: Two American oak (medium-to-heavy toasting) and two French oak (medium-to-light toasting). The barrels were infected with Brett but received hot and cold water wash and SO2 gas at the winery before transport to the research facility. Each barrel had approximately 30 staves with 25 mm thick midpoints.The 16 L barrels were inoculated with commercially prepared Cabernet Sauvignon and then each type of barrel and type of toasting was inoculated with two different strains of Brett. Thus eight treatments in total. There were …

Immobilisation of yeasts on oak chips or cellulose powder for use in bottle-fermented sparkling wine

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By Karien O'Kennedy
This study had two aims: to develop and compare yeast immobilisation processes with two wine-compatible supports (oak chips and cellulose powder) and to compare two yeast strains immobilised with these two processes to free yeasts in bottle fermented sparkling wine production.
Experimental layout: IOC18-2007 (Prise de Mousse) commercial yeast and Enolab55A (isolated from organic Spanish wine) were immobilised on oak chips and cellulose powder (Agrovin S.A.). Electron microscopy confirmed adherence of both yeast strains to the immobilised supports after lyophilisation.Vinification trials were conducted on a base wine containing 80% Macabao and 20% Chardonnay.The second fermentation was conducted according to the Champenoise method.A total of 135 bottles were fermented.                     No riddling agents (containing bentonite) were added.Bottles were kept at 11 – 13°C for 9 months.Riddling was conducted via an automated gyropallette and yeast sedimentation eff…