(Image: Louise Dignand/Millennium Images UK)
Mmmm, I think I can detect a kiwi yeast in that Sauvignon Blanc. A winemaker’s practices and the climate tend to get much of the credit for the taste or aroma of a wine, but research is starting to show just how important microbes can be for creating a distinctive taste.
The characteristics of the environment where a crop grows and the methods of a winemaker are collectively known as the terroir. They are known to influence the taste of products such as wine, coffee and cocoa.
Even though we know microbes affect crops as they grow and different types of yeasts are used to create different tastes during the fermentation process, studies into the contribution of local microbes are only just starting to kick off, says Matthew Goddard from the University of Lincoln.
Previous research by Goddard and Sarah Knight at the University of Auckland in New Zealand has shown that there are different varieties of the yeast Saccharomyces cerevisiae in vineyards in different regions in New Zealand. But it was unclear whether and how they affected the wine produced from grapes grown in those areas.
That special 10 per cent
Now they have isolated yeast from six regions and used them to ferment the same batch of grape juice from Sauvignon Blanc fruit, which has been sterilised to kill off any existing microbes.
Then they analysed the concentrations of 39 flavour-imparting chemicals in wines produced from the different yeasts. They found that 29 of the compounds varied depending on where the yeast had come from, suggesting that the local varieties of yeast affect the taste of wine, and play a part in determining its terroir. This explained around 10 per cent of variation in chemical profiles of wines.
Many winemakers already buy commercial wine yeast from other regions, but their impact is probably small compared with geography, Goddard says. “The microbial component is only one of many influences, so by itself wouldn’t weigh in massively. But we’re suggesting here that even though it’s a small component it’s still a significant component.”
Fermentation is often done using the strains of yeast present on the grapes when they are harvested, and their numbers may vary from year to year, he says, but we still get the same wine signature. “This tends to support the idea that the terroir effect is mainly driven by more important factors than yeast,” he says.
Other big taste influences will come from human-influenced factors, such as when the grapes are picked, the blend of grapes or wines, whether and for how long the wine is matured in barrels and how long it is in the bottle.
S. cerevisiae, which turns sugar from the grapes into alcohol, and affects the breakdown of many flavour-related chemical compounds, isn’t the only microbe that has a role in determining the wine’s flavour. Many other soil microbes are associated with vines as they grow, and their effects on grapes has been poorly studied.
“It seems conceivable, if not probable to me, that many of these microbes will be affecting the way the crop develops,” says Goddard. And the way that crop develops will affect things such as its taste and flavour.
He says the findings highlight an economic argument for preserving biodiversity within areas that produce agricultural products. “Here we show that the unique collection of microbes in an area contributes to the value of that product. So if you erode the uniqueness of biodiversity in an area you might erode the uniqueness of your product and thus the value.”
Journal reference: Scientific Reports, DOI: 10.1038/srep14233
More on these topics: