“Ooh yes, I’m getting a whiff of geranium, a hint of licorice and notes of sweaty socks.” Mm, okay. Even if you don’t manage to pick up half of the flavors supposedly present in a wine, we know that wines look, smell and taste different. Sure, there are different grape varieties, and people adopt different winemaking techniques to make their plonk unique. But even when you have vines that are virtually genetically identical, if you grow them in two distinct regions, the resulting wine will be different.

That is, in part, down to the fact that different areas have different geographic phenotypes – the soil, land topography, climate and agricultural techniques all vary from region to region. These are collectively termed the terroir. But it turns out there’s another factor that helps bring variety to your tipple: microbes.

You’re probably aware that microbes, or more specifically yeast, are involved in the fermentation process, responsible for the conversion of sugar into alcohol and the generation of various compounds important to wine's aroma and taste. Not only that, but microbes also influence the quality of the grape by affecting nutrient uptake from the crop’s roots, and plant health by playing a role in disease. So it makes sense that differences in the microbes themselves might have an effect on the flavor of a wine, and while genetic variations have been observed in different winemaking areas, no one had ever investigated this idea further.

To put this hypothesis to the test, a group of researchers gathered genetically different, natural sub-populations of Saccharomyces cerevisiae yeast from major winemaking regions in New Zealand. They then added these genotypes, either individually or in combination, to sterilized Sauvignon Blanc from Marlborough, New Zealand, and let them ferment away. Once the wines were made, the team analyzed their chemistry.

As described in Scientific Reports, the researchers found that the different variations of yeast imparted distinct chemical profiles on the wine. For example, those derived from Martinborough resulted in the highest concentrations of a chemical called ethyl butanoate, which tends to give sweet flavors of apple and peach. Microbes sourced from the Awatere and Wairau Valleys, on the other hand, generated the most β-damascenone, which gives honey and floral aromas.

All in all, around half of the compounds that contribute to the identity of a wine were found to be derived from fermentation by yeast. “Most of the ‘fruity’ notes in wine are in fact derived from yeast not the fruit,” co-author Matthew Goddard from the University of Lincoln, England, told AFP.

These findings do not, of course, undermine the role of terroir in wine variations, but they do add another intriguing facet that was previously undermined.