RED WINE AGING WITHOUT SO₂: WHAT IMPACT ON MICROBIAL COMMUNITY?

Abstract

Nowadays, the use of food preservatives is controversial, SO₂ being no exception. Microbial communities have been particularly studied during the prefermentary and fermentation stages in a context of without added SO₂. However, microbial risks associated with SO₂ reduction or absence, particularly during the wine aging process, have so far been little studied.  The microbiological control of wine aging is a key issue for winemakers wishing to produce wines without added SO₂. The aim of the present study is to evaluate the impact of different wine aging strategies according to the addition or not of SO₂ on the microbiological population levels and diversity.

In 2021 and 2022, microbial community were monitored on merlot red wines during the wine aging process with different SO₂ management and no SO₂ addition. An experimental design (30L) was set up in triplicate and samples were collected from vatting to bottling to perform microbial analysis: population levels were monitored by plating on agar selective media for cultivable yeasts, acetic and lactic acid bacteria. From a subset of colonies obtained on solid medium, identifications at species level were made using the MALDI-TOF MS combining with a homemade database created by the laboratory.

In 2021, our results showed that without SO₂, significant higher population levels of yeast and bacteria comparing with the sulphiting wines were present during the wine aging process. As expected, the higher species diversity was found at vatting. During the winemaking process, different species of lactic acid bacteria (10), acetic acid bacteria (3) and yeasts (8) were identified. Surprisingly, the effectiveness of SO₂ addition at the end of MLF on the lactic acid bacteria showed contrasting results considering initial SO₂ addition or not at vatting: population levels were significantly lower when SO₂ was added only after malolactic fermentation. Our results regarding the impact of SO₂ management during the winemaking process could provide opportunities for winemakers to reduce SO₂ levels.  Furthermore, for the first time, microbial communities have been monitored throughout the winemaking process, in a reduced or without added SO₂ context.