Pinking of Wine: Methods for the Detection of Causative Agents and pre- and post-pinking Treatments

Project number
P04000019

Project leader
Dr Francois van Jaarsveld

Team member
Anton Nel

Project description
The aim of the study was to investigate winemaking processes that affect the pinking susceptibility of white wine, and to provide practical guidelines for the prevention of
pinking to enable cellars to establish pinking risk practices. Sensory evaluations aimed at confirming the notion that pinking does not affect wine flavour. Researchers also wanted to establish the optimal absorbance for visually pinked wines and whether or not tasters can differentiate between pinking and other wine faults. In addition, the identification of the compounds responsible for pinking was attempted. The potential of the wine to pink increased with riper, cooler and whole bunch pressed grapes. Different press methods (such as inert presses), as well as periods of skin contact, increase the wine’s phenolic composition, which in turn constitute substrates for oxidation. Phenolic extractability of grapes increases as they ripen. Consequently vinification practices impact the chances of pinking in Sauvignon blanc that has pinking potential. Not all the chemical agents work equally well, or at all the winemaking stages where winemakers make juice/must additions, i.e. settling, fermentation and fining. Guidelines provided in this study give some insight into the best fining agents and stages of application thereof to use for the prevention of pinking.
Some yeast strains showed promising results in protecting the wines from pinking. More work, however, needs to be done regarding the protection of wines from pinking using yeast strains, particularly on other yeast cell wall factors, in addition to yeast cell wall chitin and mannoproteins that might be involved. Yeast strain selection, therefore, in addition to the above-mentioned vinification practices, will reduce/eliminate the need for the use of fining agents for pinking protection. Sunlight (UV) does decrease the pink colour considerably as determined spectrophotometrically, but not visually, questioning its effectiveness as a post-pinking treatment method. Although an aim of the study, the researchers were unable to identify the compound that causes pinking in wine.

 

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