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Showing posts from August, 2018

Yeast cell wall chitin reduces wine haze formation

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By Karien O'Kennedy

The aim of this study was to investigate the possibility that chitin contained in wine yeast cell walls can reduce protein haze formation by binding to the main cause of protein instability, i.e. chitinases in grape juice. Chitinases, in addition to thaumatin-like proteins and beta-glucanases that originate from grape juice, have been documented to be the main culprits in wine haze formation during prolonged storage, especially at elevated temperatures. It was also previously demonstrated that the addition of 1 g/l chitin can reduce wine haze with almost 50%. Chitin addition to grape juice or wine is however not permitted. Chitosan, a derivative of chitin, is permitted for use in winemaking, but only if it is of fungal origin. It has been demonstrated recently that 1g/l chitosan can render a white wine protein stable. Compared to bentonite addition of the same dosage, chitosan addition is not economically viable.
It has been observed that wine aged on yeast lee…

Effect of root trimming and planting method on early vine development

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By Lucinda Heyns

In this project, researchers wanted to determine if root pruning at planting may reduce the potential for J-rooting, without having a negative impact on young vine development. PROJECT LAYOUT: -Young Pinot noir vines, rootstock SO4 was used in the trial; -Root pruning of dormant benchgraft roots to 4cm and 15cm were evaluated; -Two planting methods were also evaluated namely digging a traditional planting hole vs using a planting spade to dig a slot in which the benchgraft was inserted. RESULTS: -Both trimming of roots to 4cm and spade planting reduced vine growth in the first year; -Reducing root length, also showed less vine growth in the second year, but planting method has no visible effect by the second year; -In years three, four and five, there was no significant difference in vine canopy growth (pruning weight) between treatments; -Despite initial reduced vigor where root pruning was applied, there was no difference in yields during year three, four and five; -The pro…

Effects of heat and water stress on grapevines

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By Lucinda Heyns

The aim of this research project was to study the interactive effects of heat and water stress on grapevine growth and ripening. PROJECT LAYOUT: Pot-grown Cabernet Sauvignon and Riesling grapevines were used. The following treatments were applied in growth chambers in a controlled environment: -Control: no stress (C) -Water stress only (WS) Soil moisture 10% lower than control -Heat stress only (HS) Hourly temperatures elevated by 10°C above 10 year average -Combined water and heat stress (WS + HS) Treatments were applied for seven days before veraison, then stress relieved and vines allowed to recover. Repeated again during veraison. Various measurements were taken and berry samples collected before and after the treatments. RESULTS: -Water stress reduced canopy growth and leaf gas exchange in both cultivars -Heat stress only occasionally reduced canopy growth -Heat stress increased transpiration in both cultivars, but only reduced photosynthesis in Riesling -In both cultiva…

Inline to online - phenolic measurements made easy

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By Karien O'Kennedy

A research team at the DVO consisting of Dr Jose Luis Aleixandre-Tudo, Dr Hélène Nieuwoudt and Professor Wessel du Toit is one step closer to simplification of grape phenolic measurements. The importance of phenolic compounds is due to their crucial role played on the colour and mouthfeel properties of red wines. In a feasibility study recently published, the phenolic content of grapes on a moving conveyor belt was measured using a contactless NIR (Near Infrared) spectroscopy instrument. This inline-online approach was compared against static measurements using the same instrument. Intact as well as crushed berries were measured following the reasoning that phenolic content would be better quantified if grapes are crushed (e.g. the phenolic information of the seed phenolics will be better exposed to the NIR light). The results were compared against two chemical reference methods. The spectral measurements of the crushed berries and the homogenate extraction pro…