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How Yeast Influences the Flavour of Your Wine

10/05/2015 05:07 EDT | Updated 10/05/2016 05:12 EDT
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Couple toasting with wine in cafe

You don't have to be a sommelier to know wines come in all different aromas and flavours. All you need to do is open up a few bottles from different regions of the world -or countries, like France, Italy, Spain and Canada. You will be greeted by a different nose from each as you swirl the glass and inhale. When you take a sip and swish it around, even more variety can be detected.

The diversity of wine regions is usually attributed to the makeup of the soil, the so-called terroir. The term has been in use since the 14th Century, although the definition has changed significantly. At first, it was used to describe the properties of wines considered to be at the highest echelon of excellence. But as time passed, the scope of the term grew to mean all geophysical aspects of the soil ranging from structure, to chemical contents and water content. Today, terroir also describes the quality and authenticity of the liquid inside the bottle.

There is another significant contributor to terroir although never given its due credit: microbes. Soil is rich with a combination of bacteria, viruses, and fungi. For years, this variation, particularly in yeasts, has been thought to contribute to the unique taste and flavour of a wine region. But, until recently, no one quite knew how.

Some attempts to demonstrate the contribution of microbes to terroir occurred at the beginning of the millennium. The method came in the form of genetics. When certain traits were changed inside the cell, so did the aroma and flavour. This alteration suggested the yeast did indeed make a difference but it could never entirely replicate an original terroir.

In 2007, even more support for microbial contribution was unveiled. Natural yeasts in the wild changed yearly due to climate and other factors within the vineyard. This suggested the yeasts contributed to the yearly changes in character of a wine from year to year. Unfortunately, while the changes could be associated, actually giving credit to the yeasts was simply not possible.

While yeast researchers continued to prove yeast were involved, another group of microbiologists were aiming to include bacteria and fungi. According to their studies, the entire microbial population of the soil, the vines, and the fruit played a leading role in how a wine turns out. Unfortunately, the evidence could not actually link flavour to a specific population as the only real determining factor turned out to be climate.

Now after all these years, the proof finally may have been found. An international team of researchers linked individual types of yeast to the sensory qualities of wine. According to the authors, this is the evidence needed to finally give microbes the respect they deserve.

Before they could get to their goal, they had to find several regions known to have different terroirs. They chose six such locations in New Zealand, a burgeoning wine region. They then chose one yeast strain from each of these regions and let them ferment the exact same grape juice. If the authors were correct, they would end up with six different wines.

At this point, the chemical analysis began. The team looked at the usual parameters associated with wine including alcohol concentration, pH, residual sugar, and acidity. But then they went a step further to look at the chemicals involved in giving wine its distinct nose and taste. This was done in order to find out if a certain yeast strain could indeed create a specific terroir quality.

Once they had collected the data and then analyzed it, there were indeed regional differences in the yeast both at the genetic level and also in the quality of the wine. In some cases, the yeast alone could account for 38 per cent of the variation. This was expected as it was the primary goal.

But, there was one surprise in store. While they expected distance to be a primary factor in the cause of terroir variation, it was simply not the case. There was no geographical or climactic factor involved in determining which chemicals the yeast produced. The authors suggested other non-tested parameters such as crop development, and possibly the microbial population of the soil could be the reasons. However, these theories were not tested.

Despite the lack of a full picture, the study revealed the importance of microbes in the development of a terroir. Depending on the natural strain of yeast used, one can expect a completely different variety of quality, aroma, and flavour. Moreover, based on some of the earlier studies, it becomes clear that as the climate changes, so will the yeast and eventually the final product.

This revelation obviously doesn't take away from the soil or the winemaker in terms of contribution to a fine glass of wine. These are without doubt major players in how a wine tastes. But the next time you take a sip of your favorite vintage, remember to give some thanks to the yeast. We now know this small organism contributes to that wonderful chemical complexity that nips at your nose and tantalizes your tongue.

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