Control of microbial development in wines elaborated by carbonic maceration

Abstract

Carbonic Maceration (CM) winemaking is typically used in different European regions. But It is paradoxical that being a traditional processing system and widely used in many wineries, some of the phenomena that take place and the parameters that characterize them are barely known. In this vinification system the intact grape clusters are placed in a carbon dioxide (CO2) enriched medium, and they immediately change from a respiratory metabolism to an anaerobic fermentative metabolism called intracellular fermentation, which is carried out by grape enzymes. But some grapes located in the lower zone of the tank are crushed by the weight of the ones above and release must, which is fermented by yeasts.

In this assay six vinifications were carried out in 300 kg tanks with grapes of the Tempranillo variety. Three tanks were vinified by carbonic maceration (CM) by adding exogenous CO2 and the other three by destemming and crushing (DC). The microbial community present at different times during vinifications was analysed. For this purpose, serial dilutions of the must or wine samples were plated onto different culture media. Total yeasts were measured by seeding onto a GYP culture medium, lactic acid bacteria (LAB) were measured by plating onto an MRS medium and acetic acid bacteria (AAB) were determined by seeding onto a Mann culture medium.

The development of the alcoholic fermentation in the CM tanks was slow, probably due to the low temperature, and the yeast population present was much lower than those of DC. This low number of yeasts caused a greater development of spoilage bacteria (LAB and AAB) in the CM tanks where there was an overlap of alcoholic and malolactic fermentations and even in some cases the MLF ended before the AF. This high presence of LAB caused a rapid development of the MLF but also an increase in volatile acidity and even the piqure of these wines.  However, in the wines made by DC the level of LAB was low, there was no overlap between the two fermentations and the volatile acidity level of the wines was correct. The AAB are strict aerobic microorganisms, and their high presence in CM tanks would indicate that, despite the addition of industrial CO2, adequate anaerobiosis was not achieved.

This work shows the microbiological risks of CM winemaking and the need to strictly control environmental conditions (temperature and the anaerobiosis) during the period in vat for the correct development of the process.

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.