Effect of sulfite addition and pied de cuve inoculation on the microbial communities and sensory profiles of Chardonnay wines: dominance of indigenous Saccharomyces uvarum at a commercial winery

The production of wine involves complex interactions between many microbial species and strains, and the microbial consortium of wine fermentations is also highly dependent upon winemaking decisions made at crush. To investigate how these decisions can affect the microbial communities and sensory attributes of commercially-produced wines, Chardonnay grape juice was allowed to ferment uninoculated, or was inoculated with a pied de cuve inoculum composed of vineyard-derived bacteria and fungi. Additionally, either 0 mg/L or 40 mg/L of sulfur dioxide (SO2) was added to the juice at crush. The bacterial and fungal communities of these wines were monitored using high-throughput amplicon sequencing (Illumina MiSeq), and Saccharomyces yeasts were identified to the strain level using microsatellite analysis. After fermentation, the wines were evaluated by a panel of wine experts to determine any differences in sensory profiles among treatments. When no SO2 was added at crush, the wines underwent alcoholic fermentation and malolactic fermentation simultaneously. Tatumella bacteria were also present in significant numbers only in the barrels to which no SO2 was added. These bacteria are likely responsible for the malolactic fermentation observed in the no-SO2 treatments and are reported here for the first time in North American wine fermentations. Additionally, all fermentations were dominated by indigenous Saccharomyces uvarum, and 150 unique S. uvarum strains were identified, with differences in strain composition as a result of SO2 addition. Wines that did not receive SO2 at crush were rated more fruity and less acidic than wines that received SO2. Wines receiving SO2 were considered to have less-desirable traits such as earthy and sulfur aroma/flavour. The pied de cuve inoculum had a limited effect on the microbial community, and only persisted when no SO2 was added; these wines did not fully complete alcoholic fermentation, and were rated to be higher in body and sweetness, and lower in acidity, than the other wines. This is the first report of indigenous S. uvarum strains dominating and completing alcoholic fermentation at a commercial winery in North America. For provenance files, R scripts, and raw data please visit: https://osf.io/kxqrn/

葡萄酒酿造过程涉及众多微生物物种与菌株间的复杂相互作用，且葡萄酒发酵的微生物菌群（microbial consortium）高度依赖于葡萄破碎环节的酿酒决策。为探究此类酿酒决策如何影响商业量产葡萄酒的微生物群落与感官属性（sensory attributes），本研究以霞多丽（Chardonnay）葡萄汁为实验材料，设置两类发酵处理：一组为自然发酵（未接种外源菌种），另一组接种由葡萄园来源的细菌与真菌构成的酒母接种液（pied de cuve）。此外，在葡萄破碎环节，向葡萄汁中分别添加0 mg/L与40 mg/L的二氧化硫（SO₂）。
采用高通量扩增子测序（Illumina MiSeq）对葡萄酒的细菌与真菌群落进行监测，并通过微卫星分析将酵母属（Saccharomyces）酵母菌鉴定至菌株水平。发酵结束后，由葡萄酒品鉴专家小组对各处理组葡萄酒开展感官评价，以明确不同处理间的感官特征（sensory profiles）差异。
当破碎环节未添加二氧化硫时，葡萄酒会同时进行酒精发酵（alcoholic fermentation）与苹果酸-乳酸发酵（malolactic fermentation）。塔特姆氏菌属（Tatumella）细菌仅在未添加二氧化硫的发酵桶中大量检出，此类细菌极有可能是未添加二氧化硫处理组中苹果酸-乳酸发酵的驱动菌，且本研究首次在北美葡萄酒发酵体系中报道此类细菌。
此外，所有发酵体系均由本土乌瓦鲁姆酵母（Saccharomyces uvarum）主导，共鉴定出150株独特的S. uvarum菌株，且二氧化硫添加与否会导致菌株组成产生显著差异。未在破碎环节添加二氧化硫的葡萄酒，其感官评级显示更浓郁的果香与更低的酸度；而添加了二氧化硫的葡萄酒则被评定为带有土腥味、硫味等不受欢迎的香气与风味特征。
酒母接种液（pied de cuve）对微生物群落的影响有限，仅在未添加二氧化硫的处理组中得以留存。此类处理组的葡萄酒未完全完成酒精发酵，且相较于其他处理组，其酒体更饱满、甜度更高、酸度更低。
本研究首次报道了本土乌瓦鲁姆酵母（Saccharomyces uvarum）菌株在北美商业酒庄中主导并完成酒精发酵。
如需获取溯源文件、R脚本与原始数据，请访问：https://osf.io/kxqrn/