Wine Quality – Thoughts on Natural or Cultured Yeast.

Wine Quality – Thoughts on Natural or Cultured Yeast.

The yeast strains that the wine makers uses is rarely if ever discussed, even though they are crucial to how the wine tastes. In simple terms yeast is responsible for the fermentation process that changes grape juice into wine.  Straight after pressing the juice is put into fermenters, at this stage we have vats of grape juice that often only has minor similarity to the wine it will produce.  It is the microbiological reaction between yeast and the juice that turns the juice into wine with its intricate flavours.  The topic on yeast and winemaking is extremely complicated and I am only going to touch on a few of what I see as the main issues with the type of yeast.

Historically grapes were harvested, pressed and then the fermentation process was started by yeasts that occurred naturally in the vineyard and the winery. In recent years, especially with “new world” winemakers the use of cultured yeast has become popular.

So wild yeasts which are individual to their location or cultured and or genetically modified  yeasts that may have nothing in common with the local regionality but can produce the required flavour profile, this is one of the winemaking dilemmas which I believe has been bought on by the corporatisation of the wine industry.  There are famous winemakers in both camps. Natural winemakers / small family wineries using the wild yeast ferment claiming the traditional way is more indicative of terroir whilst the cultured yeast camp advocate the use of cultured yeasts claiming that it is too risky leaving fermentation in the hands of potentially unknown yeast strains.

There are 3 main reasons for using cultured yeast.

  1. Cultures yeasts are  sturdier and easier to work with.  The wine maker knows that there is enough yeast to get to process happening and the flavour profile that they will achieve.  They run less to no risk of the fermentation process being slow to get going which can lead to a situation where bacterial spoilage is possible.  In this instance a bacteria such as Brettanomyces may drive the process producing a flawed wine.
  2. Cultured yeasts will withstand higher alcohol levels than wild yeast.  Due to a number of reasons the alcohol level in some wine has been increasing.
  3. By only using wild yeasts there is a risk that the indigenous yeasts are not ideal and  the winemaker can loses a bit of the control over the fermentation process and therefore control over the flavours of the final product.   With the growth of contract winemakers and large corporate producers, this is also an important commercial consideration.  By eliminating any natural yeasts and bacteria and only adding the preferred yeast a winemaker can control the final flavours that they desire,  eg certain grape types and selected yeasts will produce a particular flavour profile.   The ability to effectively buy your flavour profile is a great benefit if you are growing grapes in an area that produces substandard grapes or you are looking at producing greater volumes of wine that requires standardisation.

So why do some winemakers advocate for wild yeasts.

For some, especially natural winemakers it is a philosophical argument.  Using wild yeasts is is truer representation of the vineyard.  If you are truly wanting to represent the terroir then you need to use the yeasts from it.

It is about the elimination of added chemicals in wine manufacture and this starts by not just by using genetically modified  yeast.  The main chemical that is used in less quantities is Sulphur.  The use of cultured yeast requires the use of sulphur at the time of harvest to kill naturally occurring yeasts and bacteria so that they can be replaced with the cultured products. By using wild yeast the resultant wine should have lower sulphite levels

Producing what they see as a quality wine.  By not adding any additional yeast there will be a slower and cooler start to fermentation.  This slower fermentation  often results in a final wine that is richer and will have more complexity.

As I said at the onset this is a very complex topic and once again, there is no right or wrong but I hope that this can help you make a more informed choice of wine.


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