Protein role in wine stability

Wines of Sangiovese, Merlot, Cabernet Sauvignon, Cabernet Franc and Syrah varieties were analysed at various stages of production: pre-stabilisation, pre- and post-bottling. Proteins are present at all stages of vinification and in all wines analysed within the project. No significant correlation was found between the protein content of the wines and hot and cold turbidity. The protein content of wines correlates positively and significantly with many parameters related to phenolic composition, indicating that grape maturity and variety may play an important role in determining the protein content of must and wine. Wines in the pre-stabilisation phase contain various proteins and glycoproteins. The proteins are partly attributable to grape proteins (molecular weights between approximately 60 and 10 kDalton); larger proteins (> 60 kDalton) confirm the presence of aggregates with other molecules/particles of various natures in the wine. The wines analysed in the pre-stabilisation phase present different electrophoretic profiles that are related to the different susceptibility to form turbidity. The type of wine seems to be the variable that most affects the development of turbidity in the hot test.
The results obtained with the VINTEGRO project fit well into the model that predicts the formation of soluble PROTEINS/TANNINS/POLYSACCHARIDES complexes.