Grapes breathe

By Lucinda Heyns

Australian researchers discovered that grape berries ‘breathe’ and that they shrivel and die when they lack oxygen during ripening. Factors such as water stress or high temperatures can lead to oxygen shortages for berries. One of the discoveries was that Shiraz berries breathe oxygen differently to Chardonnay and can explain why Shiraz is more susceptible to berry shrivel. This new knowledge on how grapes take up oxygen provides the basis for further research into berry quality and cultivar selection for adapting viticulture to a warming climate.

Berry cell death and subsequent berry shrivel has implications with regards to yield loss as well as berry and wine quality. Berry shrivel leads to concentrated sugars and higher alcohols along with changes in the biochemistry within the berry. Numerous studies have focused on this phenomenon but recent findings shed new light on the mechanism behind berry cell death.

A group of Australian researchers recently t…

How late pruning affects Shiraz development and berry composition

By Lucinda Heyns

In this project, researchers wanted to evaluate the effects of late pruning and increased temperatures on the development and fruit composition of Shiraz.

Project layout

Shiraz vines in the Barossa valley were used for the three year trial. One group of vines were exposed to elevated temperatures and the other to ambient temperatures. Within each temperature regime, three pruning strategies were implemented:

Control: Conventional winter pruningBudbreak: Vines pruned at budbreak2-3 leaves: Vines pruned once 2-3 leaves unfolded
Results Late pruning delayed phenology from budbreak to veraison and delayed harvest in four out of six cases. The largest delay was 17 days in unheated vines pruned when two to three leaves had emerged.Late pruning delayed the harvest by shifting the onset and rate of ripening.Heating advanced phenology at flowering and veraison but did not hasten ripening from veraison to harvest. Heating had only a minor effect on winter pruned vines.Pruning weig…

Impact of oenological tannins on laccase activity

By Karien O'Kennedy

The aim of the study to was to investigate the efficacy of commercial tannins to protect white and red wines against oxidative browning as a result of laccase enzyme from Botrytis cinerea infection.
Project layout Five commercial tannins, representing the main botanical origins, were evaluate for their inhibitory effect towards laccase enzyme. They included three condensed tannins from grape skins, grape seeds and quebracho, and two hydrolysable tannins from nut galls (gallotannin) and oak (ellagitannin).Muscat d’Alexandrie (hanepoot) grapes harvested in 2017 from an experimental vineyard in Spain were used in the study, with half the grapes healthy and the other half infected with Botrytis spores and incubated for three weeks to allow the fungus to grow. Juice was obtained from both types of grapes, healthy and infected, and laccase activity was confirmed in the infected grape juice. For red wine trials the white juice was supplemented with 50 mg/l of malvidin-3…

Monitoring of phenolic composition during alcoholic fermentation

Researcher: Jose-Luis Aleixandre-Tudo
New Winetech funded project 2019 - The extraction of phenolic compounds during the fermentation process is influenced by many factors. Temperature, punch down and pump over frequencies, oxygen addition through aeration or microoxygenation, the presence or absence of skins, cold and post maceration techniques, among others, can promote significant changes in the levels and the composition of phenolic compounds in the resulting wines. The analysis of fermenting samples using conventional methods, such as spectrophotometric approaches or HPLC analysis, is nowadays not always possible due to time, personnel, facilities or budget constraints. The use of spectroscopy with chemometrics would provide a rapid, reliable and simple way of monitoring the extraction of phenolics compounds during this process. This technique also allows for the determination of several analytes or parameters at the same time. Additionally, infrared spectroscopy is also highly su…

Effect of mechanical pruning on vine diseases

Researcher: Francois Halleen

New Winetech funded project 2019 - The objective of this research project is to study the effect of mechanical pruning (MP) on the incidence and severity of grapevine foliar, fruit and trunk diseases compared to conventional pruning. Growth responses, grape composition and morphology, wine quality and labour costs associated with MP have been investigated locally. However, the effect on the incidence and severity of major leaf, fruit and trunk diseases, especially the long-term effect in terms of sustainable production, is unknown.
Apart from an altered canopy structure, MP results in a changed microclimate around the bunch zone, which may favour the development of certain diseases. Depending on the type of MP, a significant increase in the number of pruning wounds can occur as well as wounds with larger surface areas. Trunk pathogens infect susceptible wounds. A build-up of old wood also occurs and even if renewal pruning is practiced on a 3-year rotation…

Screening for potentially novel Pinotage clones generated through irradiance mutagenesis

Researcher: Phyllis Burger

New Winetech funded project 2019 - The aim of this project is to screen and phenotype new Pinotage plants that were generated in a pilot study that focused on developing methods to induce mutations. The intention is that the mutations could lead to potentially novel clones.
In the pilot study, irradiance doses of buds were optimised and associated methods were successfully applied to regenerate viable plantlets. Three clones of Pinotage were used and a significant population of plantlets were yielded. They now need to be further screened for vegetative and reproductive traits that could eventually lead to identification and development of new ‘Pinotage’ clones.
A phased approach will be followed where the initial screening will occur in tunnels or greenhouses to identify a smaller subset with desirable traits that will eventually be transplanted to the field plot for more comprehensive phenotyping. There is high potential for new clones with specific commerc…

Measuring of phenolic compounds during winemaking using a portable spectrometer

Researcher: Jose-Luis Aleixandre-Tudo

New Winetech funded project 2019 - Despite recent advances, the measurement of phenolic compounds during the winemaking process still requires an analytical procedure that involves time, reagents, facilities and dedicated personnel. Due to this fact, the measurement of phenolics is almost absent or limited to a low number of frequencies in commercial cellars. A non-invasive fluorescence spectrometer could provide an efficient solution to measure phenolic composition during the winemaking process. The aim of the project would thus be to investigate the suitability of a fluorescence spectrometer for the quantification of phenolic parameters in wine. Fluorescence emission spectra will in this case be used to build prediction models for the quantification of phenolic composition during winemaking and ageing.

The quantification of phenolic compounds using fluorescence techniques has been widely acknowledged. The idea is to develop a special spectromete…