鈥淗mm, hint of Candida zemplinina I鈥檇 say, or is it Botryotinia fuckeliana?鈥� Wine buffs may now have to consider the microbes, along with the grape and vintage, thanks to the first complete audit of microbes in vineyards.
Nickolas Bokulich and his colleagues at the University of California, Davis, analysed the microbes on 273 samples of must 鈥� the crushed grapes from which wine is made. These came from eight wineries across the four major growing regions in California in 2010 and 2012.
Just as wine flavour varies by region and grape type, so do the microbes present. Lactic acid bacteria was most common in Napa and on Zinfandel grapes. These bacteria can spoil wine by causing 鈥渕ouse urine鈥� flavours, or improve it by turning malic acid into lactic acid, which adds tanginess. Zinfandel grapes also had larger populations of yeasts that improve the 鈥渃omplexity鈥� of wine.
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Region-wise, the musts from wetter, coastal areas contained the highest levels of fungi that cause mildew and other types of rot. The culprits included Erysiphe necator which causes powdery mildew and leaves wine with a mouldy taste, and B. fuckeliana, whose laccase enzymes turn wine brown and disrupt fermentation.
Bokulich says he expects similar microbial fingerprints to exist for all wine-growing regions. 鈥淏ut until we look, we just don鈥檛 know,鈥� he says.
鈥淭he approach makes it possible to ascertain which specific microbes and combinations of microbes are more or less important for the quality of a given wine in a given vineyard over time,鈥� says at the University of Florida in Gainsville, who studies the evolution of yeast. 鈥淭he consistency of the most important microbes over time may ultimately contribute to the quality of the wine and reputation of vineyards,鈥� he says.
Journal reference: PNAS, DOI: 10.1073/pnas.1317377110
