Microbiome composition and dynamics while grapes turn to wine

Abstract

Microbial composition and activity were recorded during preparation of Pinot blanc (“Rulandské biele”) from one vineyard during the years 2018, 2019, and 2020. Both fungi and bacteria are important for primary fermentation and malto-lactic fermentation, therefore total DNA and total RNA were isolated, and genes for 16S and 28S rRNA were amplified to determine both bacterial and yeast profiles. Four phases of wine production were selected for testing. We tested the initial grape juice right after crushing the grapes, must ~2-3 days post inoculation, actively fermenting must and finally – young wine before filtration. We experimented on 3 batches with addition of selected strains of Lachancea thermotolerans, Metschnikowia pulcherrima and commercial strains of Saccharomyces cerevisiae. The most apparent was seasonality and the effect of weather at given year. Naturally occurring yeast Hanseniaspora was detected alongside major players like S. cerevisiae. The most dominant bacterial genera were Gluconobacter, Komagataeibacter and Acetobacter. We were able to detect contaminating coliform bacteria as a result of unexpectedly warm and humid conditions during the harvest in 2018. This method even detected plant pathogens Penicillium, Botrytis, and Alternaria in some samples, and might be indicative of the health of a vineyard.