Effects of post-fermentative cold maceration on chemical and sensory characteristics of Syrah, Cabernet Franc and Montepulciano wines

Astringency sensation decreases slowly during the aging of red wine. Complex reactions of condensation and precipitation of wine polyphenols are involved in this phenomenon. Wine composition and conditions of aging, such as temperature and oxygen availability, strongly influence evolution of the phenol matrix. Recently, a Post-Fermentative cold Maceration (PFM) technique was tested with the aim of accelerating reactions leading to the reduction of astringency and exploiting chemical compounds not extracted from the solid parts of grapes during the previous traditional maceration phase. To this purpose, an innovative maceration system was engineered and used to perform PFM trials on marc derived from vinification of different varieties of red grapes. Syrah grapes, vintage 2012, were used for the experiment on a pilot scale. In 2013, PFM trials were performed with Syrah, Cabernet Franc and Montepulciano grapes vinified on an industrial scale. For each trial, perfectly healthy grapes were manually harvested at maturity. At the winery, grapes were crushed, destemmed and fermented in a stainless steel tank, at 28 °C. At the end of fermentation, free-run wine was used as control in the experiment. After racking, wet marc (marc/free-run wine ratio about 3/1) was transferred to the maceration system, added with 5 Kg/hL of dry ice and processed for 48 h at 6 °C, mixing every 6 h for 15 min. At the end of the cycle, wine (WPFM) was drained and marc was gently pressed inside the system. In 2012, during PFM treatment of Syrah, a significant decrease of total polyphenols, proteins and Astringency Mucin Index (AMI)(Fia et al. 2009) was observed. Total polyphenols, proteins and AMI remained lower than that detected for the control up to 6 months. In 2013, WPFM and control wines were aged for 18 months in oak barrel. After 6 months, chemical parameters and sensory attributes of the wines were evaluated. Total polyphenols, proteins and the Astringency Mucin Index (AMI) of WPFM were lower compared to the control wine. WPFM wines reached protein stability while the controls were unstable. Color intensity of the WPFM samples was high but lower than that of the control while hue was similar. The effects of PFM treatment on sensory characteristics of the wines vary depending on grape variety. Syrah and Cabernet Franc elaborated with PFM technique were perceived as significantly less astringent and bitter compared to the control wines. PFM treatment also influenced smell characteristics of Syrah and Cabernet Franc in term of oak and fruity aroma. After 6 months, the sensory profile of Montepulciano wine from PFM treatment did not show differences compared to control. After 18 months, all wines were significantly less astringent compared to control. The obtained results indicate that the PFM treatment can rapidly induce a noticeable reduction of wine astringency, probably due to a selective precipitation of the most reactive polyphenols with grape proteins.