The impact of grape processing and carbonic maceration on the microbiota of early stages of winemaking

Aims: The work investigates the impact of grapes processing at the beginning of winemaking on the composition of microbiota during the oenological fermentations and on the composition of obtained wines. Methods and Results: The experiments were conducted in a biodynamic winery to exclude interference due to microbial starters. Three winemaking protocols, with different pre-fermentative management of grapes, were followed by plate count and next generation sequencing on 16S for bacteria and internal transcribed spacer sequencing (ITS) for yeast. Chemical and sensory characterization of wine was performed. The grape processing influenced the evolution of microbiota (especially lactic and acetic acid bacteria) and the fermentation rate. The highest biodiversity was observed in the experiment carried out with whole grapes and carbonic maceration, with the presence of bacterial groups not usually found in winemaking (Bacteroidales, Clostridiales, Oscillospira). The different microbiotas influenced the organic acid profile of wines, the content of biogenic ammines and the perception of organoleptic descriptors linked to the vine cultivar (Syrah). Conclusions: Carbonic maceration impacts on the evolution of the microbiota and the wine features. The absence of addition of starters and sulphur dioxide would seem to be correlated with the high microbial biodiversity. Significance and Impact of the Study: Carbonic maceration is a traditional winemaking practice, today there are difficulties in its managing because the anaerobiosis stimulates spoilage micro-organisms. The work elucidates the reasons of these difficulties and identified some microbial groups rarely associated with winemaking. The ratio of ethanol accumulation along with physical management of grapes and the supply of oxygen during the early stages of winemaking are powerful instruments of oenological variability, able to offer new possibilities to winemakers in order to defining the quality of red wines.