"Hmm, hint of Candida zemplinina I'd say, or is it Botryotinia fuckeliana?" Wine buffs may now have to consider the bacteria, along with the grape and vintage, thanks to the first complete audit of bacteria in vineyards.
Nickolas Bokulich and his colleagues at the University of California, Davis, analysed the microbes on 273 samples of must – 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 "mouse urine" 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 "complexity" of wine.
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. "But until we look, we just don't know," he says.
"The 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," says John Aris at the University of Florida in Gainsville, who studies the evolution of yeast. "The consistency of the most important microbes over time may ultimately contribute to the quality of the wine and reputation of vineyards," he says.
Journal reference: PNAS, DOI: 10.1073/pnas.1317377110
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