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Showing posts from October, 2017

Postharvest ozone fumigation of Petit Verdot grapes to prevent use of sulphites

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The aim of this research was to evaluate the application of ozone as a sanitizing agent of grapes before vinification, in order to reduce the use of sulphur dioxide.
Project layout:  -500 kg of Petit Verdot grapes were hand harvested and placed in perforated boxes (60 x 40 x 30 cm); -Boxes were placed in a cold room overnight where grapes were fumigated with ozone; -Control grapes were also packed in perforated boxes and placed in a cold room; -Control grapes were powdered with potassium metabisulfite – without any specific calculation – to lightly cover the top layer of bunches; -Both batches were vinified the next day. Refer to article for winemaking protocol.
Results:  -Ozone treatment did not affect sugar concentration, TA or pH of grapes; -Overnight cold storage also had no effect on TA, pH or sugar concentration in the control; -Ozone significantly increased concentration of anthocyanin (19% increase) and skin tannin (14%); -Ozone significantly reduced acetic acid bacteria, lacti…

Effect of row orientation, trellis system and shoot and bunch position on variability in S. blanc

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The aim of this study was to determine to what extent harvest date, row orientation, trellis system and position of fruit in the canopy affects berry and juice composition in Sauvignon blanc.
Project layout:  -Two adjacent blocks of Sauvignon blanc were used for this trial. One block with E-W row-orientation and the other with N-S row-orientation; -Two trellis types were established in each block namely Scott-Henry (S-H) and vertical shoot positioning (VSP); -Progress of flowering was monitored and fruit exposure assessed; -The position of bunches on shoots was also considered to determine whether it affects flowering date; -Refer to article for more details on sampling strategy and trial setup.
Results:  -Many of the differences in fruit composition within vines at harvest can be attributed to the timing of flowering. This can in turn be a reflection of environmental and management responses from early in the current growing season and/or during inflorescence initiation in the year be…

Filtering out Brett

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By Karien O'Kennedy
The aim of the study was to compare the efficacy of filters with different compositions and pore sizes to remove Brettanomyces from wine. 
Project layout:  A red wine, treated with hydrogen peroxide to remove SO2, was inoculated with Brettanomyces at a rate of 1.6 x 106/ml. Seven different filters/pore sizes were compared for efficacy using 47 mm diam discs of each filter medium. The filters evaluated were polypropylene (PP, 0.6 and 1 µm), borosilicate glass microfiber (GF, X and V) and polyethersulfone membrane filters (PES, 0.45, 0.65 and 1.0 µm). Filtered wine was collected and plated for microbial cell counts on plates containing bacterial and fungal inhibitors.
Results: -The PP filters had very low retention for Brett cells. The 0.6 µm filter was marginally better than the 1.0 µm one. -In the case of the GF filters only the GF X filter had a good retention efficacy for Brett. GF filters are depth filters recommended for use prior to membrane filtration. -…

Thiol levels in Chenin blanc wines

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The aim of this study was to determine the volatile thiol levels in commercial South African Chenin blanc wines. Volatile thiols were previously measured as part of a bigger study investigating the effect of skin contact on Chenin blanc wine quality and style. However, the current study is the first study world-wide specifically investigating the presence and importance of volatile thiols in Chenin blanc wine.
Project layout:  Sixty five commercial dry South African Chenin blanc wines were analysed for volatile thiol concentrations. The two thiols analysed were 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA). The method utilised was a UPLC-MS/MS. Wines of three different ages were analysed: one, two and three years old.
Results: 3MH and 3MHA were both found in concentrations above their aroma thresholds indicating that these two components contribute significantly to Chenin blanc aroma.The wines displayed large differences in concentrations of these two volatile thiols.T…