Effect of certain treatments to prevent or partially reverse the pinking phenomenon in susceptible white wines

Abstract

Pinking is a phenomenon occurring in certain white wines produced under highly reductive conditions which occasionally develop a pink colouration when suddenly exposed to air. The pink colouration gives the impression of wine being stained with red grape pigments, but in fact the phenomenon is a transformation in the presence of oxygen of some specific phenolic compounds found in the susceptible varieties. In our experiments two white wines based on Sauvignon blanc and Chardonnay, respectively, were found to have a high potential toward pinking. This study evaluates the potential of certain treatments to prevent the development of pinking or to partially reverse it after occurrence. Treatments tested involved the addition of 20 to 40 mg/l ascorbic acid or 5 to 30 mg/l of catechinic tannin prior to bottling. Both types of treatments had the potential to prevent pinking, irrespective of dosage used, as long as a normal concentration of free SO2(above 0.8 mg/l molecular SO2) was maintained in the wines. Other treatments tested for bottled wines already developing a pink shade were the exposure of the bottle to UV light or the keeping in complete darkness, respectively. In the absence of any other pinking preventive measure both treatments proved to have a certain effect upon reversing the phenomenon. The UV light treatment shows more potential to reverse pinking than darkness and it may work even better on bottles with lower UV light filtering power (in this experiment Antique green glass bottles, with 70–80% UV reduction effect, were used). Differences among the responses of varieties are also present, with Chardonnay being less responsive to antioxidants than Sauvignon blanc. The parameters determined for the evaluation of pinking level are: Pinking potential index (PPI), proanthocyanidins (PAC), co-pigmented anthocyanins (Cp), polymeric pigmented anthocyanins (P) and total pigments (TP), as well as the absorbtion at 420 nm (for browning), 500 and 520 nm (for pinking), 620 nm (for blue shades).