Influence of must fining on wine pinking: relationship between electrochemical and colorimetric measurements and pinking attitude of wine

Abstract

AIM: “Pinking” is a term used to define an abnormal pink coloration assumed by white wines in certain cases. Despite the are many hypotheses about the causes of this phenomenon, pinking still represents an issue for the wine industry. In the absence of reliable preventive strategies, wineries often rely on treatments such as charcoal fining, which is also negatively impacting wine aroma. This study aims at evaluating the potential of different fining agents based on animal or vegetal proteins to prevent wine pinking when applied at the level of must clarification. The work was carried out on Lugana wines, which is well-recognised as sensible to pinking problems.

METHODS: Two experimental Lugana musts were obtained by applying a standard winemaking protocol and were then clarified with different commercial preparations based on vegetal proteins or casein, alone or in combination with PVPP. A control only using pectolytic enzyme was also prepared. Finings were carried out at 4°C for 16h, and the clear must (200 NTU) was then fermented in controlled conditions. At the end of fermentation all wines were bottled with 25 mg/L of free SO2. Musts and wines were submitted to linear sweep voltammetry, colorimetric (CIELab) and spectrophotometric analyses. Pinking was assessed by CIELab.

RESULTS: Must fining with products based on combination of vegetable proteins and PVPP allowed significant reduction of must content in oxidizable compounds assessed by voltammetry, and this difference was still detected in the finished wines. After one month of bottle aging (free SO2 being 20 mg/L in all wines) pinking was detected for all wines except for those obtained from musts treated with potato or pea protein combined with PVPP. Voltammetric features of the must were shown to be well correlated with the risk of wine pinking. Analysis after one year of bottle aging confirmed the potential of fining to prevent pinking.

CONCLUSIONS: The type of fining agent used in must fining affects the occurrence of pinking in the finished wines. Vegetable proteins in combination with PVPP showed high potential for pinking prevention. Voltammetric analyses could be a promising tool for rapid assessment of the efficacy of fining treatments towards pinking.

ACKNOWLEDGMENTS:

The present work was financially supported by Biolaffort.