Terroir and Yeasts Revisited
Once I learnt of it, and really began to understand what it was telling me, the concept of terroir always made sense; in essence, two different sites will always give, even though the variety and the vinifications are the same, two different wines. So a Bourgueil from Les Malgagnes will taste different to one from Les Quartiers, even though both come from the same cellar and the same vigneron. That is terroir.
Defining what lies behind terroir, however, is fraught with controversy; understanding why one site gives different wines to another seems an impossibility. We have climate, soil, bedrock, aspect, drainage and more. Should we include the winemaker? Should we include the local microbiology, either that in the soil, on the grapes or in the winery? All have been mooted.
The thought that terroir might be a yeast effect is a tempting one. After all, as far as I am aware, few agricultural products show this ‘regionality’. Please correct me if I am wrong, but a peach from one orchard tastes much like a peach from an orchard down the road, provided the variety and agriculture is the same, but two wines from fruit grown just metres apart can be radically different. The key difference between the two products is that wine has undergone a microbiological transformation, a process not relevant to the world of peaches (unless you’re into home brewing I guess).
While there is no doubt different yeasts imbue wines with different characteristics (cultured yeasts are sold on this very basis – some types are ‘neutral’, while others produce more aromatic results) I have stated before I find the idea that terroir differences might be due solely to yeasts rather an unlikely one.
A recently published paper from Matthew Goddard and team from the University of Auckland School of Biological Sciences would appear to support my thoughts, even if the authors argue it in the other direction. The authors fermented many (over one hundred) sterilised samples of Sauvignon Blanc juice with genetically diverse isolates of Saccharomyces cerevisiae from six different regions of New Zealand. They then looked at an array of volatile compounds to see if they differed from one S. cerevisiae ferment to the next, and therefore from one region to the next.
Here’s the science bit, part one. Goddard et al found that when the juice was fermented with single strains, there was some difference between the aromatic profiles of the wine that resulted. But there are three important points here: (1) this isn’t surprising; we know different yeasts produce wines of different aromatic qualities, (2) the differences between the six regions when tested with single-strain ferments was only 10% down to the yeast, so even with a single-strain ferment the aromatic differences were 90% due to other (mostly unknown) factors, and (3) the aromatics differed from batch to batch – variation between batches accounted for 7% of the differences in levels of the volatile aromatic compounds (nearly as much as the yeast-effect, which was just 10%).
With the yeast effect hardly stronger than batch variation, is it really a plausible candidate for the cause of terroir?
And here’s the science bit, part two. Because part one is not applicable in the ‘real world’ (because wild ferments involve many different yeasts all working at the same time – they are not single-strain ferments) the team also did co-ferments, with not one strain from each region, but six single-region strains mixed together. With these fermentations, there was no statistically significant relationship between the region from which the strains came and the aromatic profile of the wines. Now this might just be a problem with sample size – perhaps running the test again with several hundred more samples would solve this (yes I know that is easier said than done – this paper reflects a lot of hard work).
Even so, for the moment it appears to me that any regional ‘yeast effect’ is identifiable but small with a single strain, but this appears to be lost in the mix once you have a body of yeasts working together, as in the ‘real world’.
Perhaps yeasts do contribute something to terroir. I am open-minded on the matter, and await some convincing research to persuade me one way or the other. But even if they do contribute, this research suggests yeasts play a minor role, which would therefore seem to indicate that the traditional view of terroir as being related to the physical properties of the site still holds true. Or at least more true than it does for yeast.