Grape juice and wine proteins: evolution during fruit ripening. Impact in white wines protein haze and prevention of the risk

Mestrado Vinifera Euromaster - Viticulture and Enology - Instituto Superior de Agronomia

Grapevine proteins can play a double role in winemaking. They can have a positive effect in foamability in sparkling wine, but their presence in wine can also be responsible for the wine haze risk (WHR). So, this study is split in two parts as follows: the first part investigated the trend of grape protein content along with the ripening process. Oenological parameters of healthy grapes of cultivars Chardonnay Blanc and Pinot Noir (Vitis vinifera L.), vintages 2012, from the Champagne region at different maturity stages, were collected to investigate the relationships between grape berry maturity degree (MD), and other oenological parameters, such as protein content. The results in both varieties showed an increasing trend of total protein contents (analysed by electrophoresis) during the ripening. Strong correlations have been found among grape berry MD and almost all the parameters in both cultivars. The second part of the work, investigated the use of potential alternative to the use of bentonite for colloidal stability. Indeed, clouding and haze formation are serious aesthetic problems especially in white wines which are caused by the presence of flocculated grape proteins. To overcome this problem and stabilize white wines bentonite is widely used, which allows the easy removal of grape proteins. As known bentonite entails many drawbacks, such as loss of wine volume and stripping of aromas. Thus, this study evaluated the use of an alternative treatment to achieve a colloidal stability without the use of bentonite. Aspergillo-pepsins (AGPs) was added in the aim to stabilize a Sauvignon blanc 2017 grape juices from Amboise (Vallée de la Loire - France), with and without heat treatments (75 °C, 1 min) prior to fermentation. Without heating, AGPs showed a low proteolytic activity. When combined with must heating, more than 90% of the total proteins disappeared in both cases (heating carried out before and after enzyme addition) proving in this case that the heating applied alone was sufficient in fact

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