From spontaneous apple fermentations to Calvados: Insights into its aromatic complexity

Calvados is an apple brandy from Normandy made by distilling cider. In order to better manage the calvados quality, the aim of this study was to correlate microbial kinetics and diversity and chemical and VOCs profiles during the fermentation process of cider. Bacterial and fungal diversities and VOCs were investigated from ten ciders for distillation using Illumina MiSeq sequencing technology and chromatographic techniques. A microbial profile comparison was performed by MDS/PCoA according to fermentation steps. The tanks were grouped according to their bacterial composition found at the end of the alcoholic fermentation and at the end of the maturation process: A/B/D1/D2 (Group 1), C1/C2/C3/E1 (Group 2), and E2/F (Group 3). Interestingly, the same three groups were discriminated by PCA analysis of the 45 VOCs of the microdistillates of the ciders of the ten tanks after maturation. Several species of Lactobacilliaceae and Oenococcus oeni, were found to be the main species during cider malolactic fermentation for the tanks of the first group while the other tanks were dominated by Serratia sp. Malolactic fermentation coincided with alcoholic fermentation, except in tanks with few lactic acid bacteria. Cytoscape identified interactions between microbial clusters and VOCs, linking Lactobacilliaceae and Oenococcus sp. to ethyl lactate and several VOCs, while Dekkera sp. correlated with high phenol volatile levels and volatile acidity. This study advances understanding of microbial interaction and VOCs composition in spontaneous cider fermentation.