Microbial populations and community dynamics during alcoholic and malolactic fermentations can affect the sensory attributes of the final wine. Factors influencing the microbial population include SO₂ addition, length of cold soak or cold settling, temperature, and yeast inoculation history. It is common practice to inoculate grape must or juice with Saccharomyces cerevisiae for alcoholic fermentation (AF) and Oenococcus oeni for malolactic fermentation (MLF). Changes in microbial populations and communities were monitored throughout a Chardonnay fermentation. At the strain level, we used a culture dependent approach, whereby strain typing was accomplished by microsatellites for S. cerevisiae and by VNTRs for O. oeni. At the species level, we used a culture-independent method using Illumina Miseq NGS in conjunction with propidium monoazide (PMA). Yeast and bacterial diversity and composition were compared among the following inoculation treatments: co-inoculation of O. oeni and S. cerevisiae in grape must, inoculation of either S. cerevisiae or O. oeni in grape must, post-AF inoculation of O. oeni in inoculated or spontaneous fermentations, and uninoculated wine. Bacterial populations, S. cerevisiae populations, yeast community diversity and composition, and chemical and sensory profiles of the finished wine were measured. O. oeni inoculation prior to AF resulted in lower bacterial species diversity than post-AF O. oeni inoculation and uninoculated wine. Spontaneous AF resulted in greater diversity of yeast, bacterial species, and S. cerevisiae strains. Principal component analysis of sensory data showed trends among treatments. Sensory profiles indicated that both O. oeni and S. cerevisiae inoculation changes sensory attributes of the final wine. The practice of inoculating must with yeast and bacteria impacts microbial composition, resulting in less diversity of microbes, which in turn reduces positive sensory attributes of the wine such as body and aftertaste, tropical fruit, vanilla, and oak flavors, and buttery and vanilla aromas.

Funding Support: BC Wine and Grape Council, and Natural Sciences and Research Engineering Council (NSERC) Engage