Pinking Stability in White Wine Linley Schultz Alvi's Drift Private Cellar 5th of June 2015

Overview Background Why is it an issue? Susceptible wines Cause Measurement Prevention Treatment Conclusions and summary

Background Pinking describes the problematic dis-colouration which sometimes occurs in white wines during storage or after bottling. It isn't related to colour extracted from red grapes The pink colour obscures the natural green or yellow colour of the wine This can give the impression of oxidation Oxidation is a separate issue, but both are related to the exposure to oxygen after fermentation. The colour can range from the faintest of pink hues to very pronounced pinking The problem is mainly aesthetic as aroma and taste of the wine is generally not affected.

Why is it an issue? If pinking doesn't affect the aroma or taste of wine, why is it a problem. Aesthetics matter People taste with their eyes We have to put a product in the bottle which is stable and in line with their expectations Veritas has had a zero tolerance for pinking in the sauvignon blanc class in the past. Almost one third of wines were disqualified for pinking

Which wines are susceptible Many white wines are at risk if they have been reductively handled prior to fermentation. Susceptible varieties from a South African perspective are: Sauvignon blanc Chenin blanc Crouchen Hanepoot Riesling

Cause Pinking is a relatively recent problem caused by the introduction of modern winemaking techniques Particularly inert gas, refrigeration and more stringent use of antioxidants such as SO2 and ascorbic acid Only for wines handled reductively as juice It was described as an issue by Singleton as far back as 1972 Reaction of pro-anthocyanins with oxygen after fermentation

Measurement Sensitivity of assessment is important From a practical perspective, if you can't see it, it isn't a problem However, it can form in the bottle after bottling Measurement can be with the eye, which is very sensitive to pinking. Use a clean glass on a white surface and wrap a white piece of paper around the glass to remove any interfering light source If you can see any pinking at all, it will be rejected at Veritas Absorbance at 500 to 520nm

Measuring Pinking Potential In a very young wine, prior to filtration, you can leave the wine in a half full bottle on a table. The top layer of the wine will start to turn pink due to the interaction with oxygen within a few hours depending on the SO2 levels Similarly, a filtered wine ready for bottling, can be put in a half full bottle and put in a dark cupboard overnight. Adding H2O2 will speed up the process. This can give an indication of susceptibility. This test needs to be done in darkness as the pinking is UV sensitive. Pinking test in a laboratory. Addition of H2O2 and measuring the absorbance at 500 or 520nm They will give you a number which effectively tells you if the wine is stable

Prevention So, you have your result from the lab telling you the wine is unstable. What now? Treatment with PVPP to remove precursers Treatment with ascorbic acid, to scavenge any DO2 pick up at bottling. Addition of more SO2 gives added protection Measure DO2 pick up at all stages of the bottling process

Treatment A wine which has pinked in the tank can be treated with PVPP A bottled wine which turns pink in the bottle can be treated by placing it in the sun until the colour disipates. The pinking tends to reduce over time

Conclusions Some varieties are more susceptible than others Only occurs in wine where juice was reductively handled Oxygen is the enemy Measure your DO2 pick up to assess the risk of your bottling facility Test for pinking stability before bottling Treat the wine before bottling if you have concerns If you have pinking problems, you are probably trying to make a wine reductively, but are just not quite managing the process all the way through to the end. No great cost involved and it will improve your control of the process if you address these issue.

The End Thank you for listening and many thanks to Dr. Bryce Rankine for writing “Making Good Wine”.