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Showing posts from July, 2019

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…