Abstract: The present invention relates to a winemaking process using the traditional method of vinification except that, after fermentation, a chitosan-based film is placed in contact with the wine and no sulfur dioxide is added. The present invention also relates to a process for preparation of a chitosan-based film by modification of the chitosan with natural compounds, which allows to produce chitosan films stable in acidic medium, with high antioxidant activity, while maintaining the antimicrobial activity. In one embodiment, the films are prepared by covalent linkage to the chitosan of molecules, such as genipin, which results in decreasing its solubility in acidic medium, and also of molecules with high antioxidant activity, such as caffeic acid, or grape and wine extracts rich in compounds with antioxidant activity.