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Grapevine bud fertility under conditions of elevated CO2

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By Lucinda Heyns
The aim of this study was to determine how elevated CO2 levels affect bud fertility and yield of field-grown Riesling and Cabernet Sauvignon in the Rheingau area in Germany.
PROJECT LAYOUT: It has been shown that yields increase under elevated CO2 (eCO2) levels but the effect of bud fertility under eCO2 and its relation to yield has not been researched. In this trial, conducted over two years, 2016-2017, both Riesling and Cabernet Sauvignon vines were investigated. The following was recorded under conditions of ambient CO2 concentration (aCO2) and eCO2: Number of inflorescence primordia (IP) per node, The cross-sectional area of the IP,The incidence of primary bud necrosis (PBN), in grapevine compound buds.Yield parameters at harvest was then related to the data.
RESULTS: In Riesling: No differences were found with regard to IP number per node or subsequent number of bunches per shoot in either of the treatments.In the eCO2 treatment, compound buds of Riesling had larg…

Effects of heat events on Shiraz berry composition

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By Lucinda Heyns
In this project researchers wanted to determine what the effects of a single heat event, as well as cumulative effects of a number of heat events are on Shiraz berry composition and tannins.
PROJECT LAYOUT: In order to control the environment, the experiment was done in a greenhouse on potted Shiraz vines. To simulate a heat event, temperatures were increased by 6°C while fruit and canopy light exposure remained unchanged. The following treatments were applied: Control (C )Heat event at the end of fruit set (HE1)Heat event prior to veraison (HE2)Heat events at both end of fruit set and veraison (HE1&2)
Temperatures inside the greenhouse was affected by outdoor temperatures. During HE1, maximum temperatures inside the greenhouse reached 45°C while reaching 40°C at HE2. Berries were regularly sampled from fruit set to maturity, where primary and secondary metabolites as well as tannins were analysed.
RESULTS: Photosynthesis was significantly decreased for the heate…

The effect of high temperatures on the stability of Potassium Polyaspartate (KPA)

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By Karien O'Kennedy
The aim of the study was to evaluate the efficiency of different dosages of KPA over time in wines exposed to high temperatures. Potassium polyaspartate has recently been approved for use as an additive to wines to render them tartrate stable. It has a similar mode of action to metatartaric acid, mannoproteins and CMC in that it prevents tartrate crystal formation. In contrast to CMC it can be used on red wines since it does not affect wine colour.
Project layout: Four different wines were used for the experiments that started in October 2016: two red wines (Chianti 2013 and Chianti 2015) and two white wines (Catarratto 2015 and Chardonnay 2015). Wines were filter-sterilised and KPA added in three dosages: 5, 10 and 15 g/hl to the red and white wines. CMC was added in the same dosages only to the white wines for comparison. Maximum recommended dosage by the OIV for both products is 10 g/hl. The wines were all protein stable before addition of KPA and CMC.Wines w…

The effect of PVPP treatment on rosé during fermentation

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By Karien O'Kennedy

The aim of the study was to evaluate the effect of PVPP on colour, polyphenol and volatile thiol content during rosé fermentation.
Project layout: Blends from Grenache noir and Merlot free run juice in two different ratios were used.The juice was fermented with 20 g/hl Zymaflor X5 and 30 g/hl Superstart at 20⁰C.Four different dosages of PVPP were added to the must at the end of the first third of fermentation. Colour, polyphenol content and volatile thiols were measured after the completion of fermentation.Results:
The higher the PVPP dosage used the more colour loss was observed.PVPP affected mostly flavanol, flavonol and anthocyanin concentrations (decreasing it with increased dosages). Lower dosages of PVPP (20 – 40 g/hl) increased volatile thiol concentrations compared to the control wine. The researchers hypothesised that it is most probably as a result of the early removal of polyphenols that could have potentially oxidised into quinones at a later stage duri…

Influence of application of elicitors on grape berries and wine

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By Lucinda Heyns
In this study, researchers wanted to evaluate the effect of pre-harvest application of elicitors such as methyl jasmonate (MeJ) and benzothiodiazole (BTH) on the composition and structure of grape berry skin cell walls. The extractability of the phenolic compounds during winemaking was also investigated to determine if wine quality was improved.
PROJECT LAYOUT: The trial was conducted over two consecutive seasons in Spain.Merlot, Cabernet Sauvignon and Monastrell were used in the trial.All treatments were performed in triplicate.There were three treatments namely control, MeJ application and BTH application.Treatments were applied twice, first at veraison and then one week later.Grapes were harvested at optimum maturity, some berries kept for analysis and from the rest of the grapes, wine was made according to a standard winemaking protocol. RESULTS:
The treatments delayed the maturation process in all varieties when rainfall was low.Application of MeJ and BTH during…

Effect of increasing temperatures on secondary metabolites and aromas

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By Lucinda Heyns
The aim of this study was to better understand the effect of increased temperatures on secondary grape metabolites such as phenolics and aroma precursors.
PROJECT LAYOUT: The field study was conducted over two years in Bordeaux, on Sauvignon blanc and Cabernet Sauvignon vineyards.Two treatments were applied namely a control and then heat treatment from fruit-set to maturity. The heat treatment continuously increased berry temperatures by about 1.5°C. The moderate increase in temperature simulated the predicted effects of climate change on temperature in Bordeaux. Berry samples were collected four times from bunch closure to maturity. Primary and secondary metabolites were measured in the berries and skins.
RESULTS: The heat treatment: did not affect primary metabolites such as sugars and organic acids;did not affect berry weight or tannins;reduced amino acids and anthocyanins;sometimes reduced IBMP levels, which could be beneficial;significantly reduced thiol related ar…

Increasing volatile thiol precursors with sources of sulphur

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By Karien O'Kennedy
The aim of the study was to determine the influence of different sulphur sources on the consumption of thiol precursors and the formation of volatile thiols.
PROJECT LAYOUT: All experiments were conducted in synthetic juice containing thiol precursors added in specific concentrations: 50 µg/L GLUMP and CYSMP (precursors for 4MMP) and 1000 µg/L GLUMH and 100 µg/L CYSMH (precursors for 3MH).Different sulphur containing compounds were added individually and in some cases in different concentrations to the synthetic juice.In experiment 1 elemental sulphur (1 mg/L), glutathione (50 and 70 mg/L), methionine (30 and 50 mg/L), cysteine (20 mg/L) and SO2 (20 mg/L) were added individually to the juice.In experiment 2 the three amino acids that make up the glutathione molecule (cysteine, glycine and glutamic acid) were added to the synthetic juice individually and in different concentrations.In experiment 3 four concentrations of SO2 (20, 30, 50 or 70 mg/L) were added to t…