Factors involved in the acumulation of acetic acid inside the grapes during winemaking by carbonic maceration

Abstract

Vinification by carbonic maceration (CM) is based in the anaerobic fermentative metabolism also called intracellular fermentation (IF). It happens inside the whole grapes by its own enzymes when they are subjected to anaerobic conditions. The vinification conditions favour microbiological development, and sometimes, a great accumulation of acetic acid. In the present work we studied the effect of both temperature and the type of carbonic anhydride applied to the tanks (exogenous gas or generated by fermentation) on intracellular fermentation in order to minimize the increase in volatile acidity in CM vinification.
In this work, eight vinifications were carried out in 12-liter stainless steel tanks in order to study four vinification conditions in duplicate: Inoculation with a commercial active dry yeast (ADY) Saccharomyces cerevisae to generate the necessary CO2 for the development of the anaerobic conditions at 20°C (I20) and 30°C (I30); and addition of industrial CO2 to the tanks before filling at 20°C (C20) and 30°C (C30). Every 2-3 days (days 1, 4, 6, 8 and 11) 10 whole berries were randomly collected from each tank. The grapes were crushed to obtain the must-wine, where the content of acetic acid was analysed throughout the time in the vat. The tanks were devatted when the alcoholic fermentation of the liquid was finished (6 days in I30, 8 days in I20 and C30, and 12 days in C20).
The accumulation of acetic acid was greater at higher temperatures, both in the inoculated deposits and in those added with exogenous CO2. However, this does not imply that the final wines have higher volatile acidity because at fermentation temperatures of 30°C it would produce an earlier drawing off. The accumulation of acetic acid in grapes over time was also greater in deposits added with industrial CO2. At the moment of devatting, the must-wines with less volatile acidity were the inoculated ones.
In conclusion, proofs carried out in different CM conditions showed that the drawing off moment is an influential factor on the content of acetic acid inside the grapes and, therefore could play an important role in the characteristics of the CM wines obtained. In addition, the inoculation with ADY as a method of generating anaerobiosis, helps to minimize the accumulation of acetic acid inside the whole grapes during the vat. Finally, it is also important to maintain a high temperature of grapes during the period in the vat because it makes vat time shorter.
This study has been co-funded (50/50) by the European Regional Development Fund (ERDF) and the Government of La Rioja, within the ERDF operational program of La Rioja 2014-2020. It also has been financed by MCIN/AEI 10.13039/501100011033, Project RTI2018-096051.