Glycerol this, glycerol that

comments ( 0 )
July 9, 2010  posted by Louis Nel

Karien’s comments on the hype that was made about glycerol, makes me nostalgic. Everybody was caught in the frenzy to find ways to increase glycerol in wines, and people went to extremes to achieve their goal.

 Glycerol is one of the base chemicals used to make dynamite, and the commercial production of glycerol involves yeast fermentation, where SO2 is added constantly. To protect itself from the SO2, yeast produces glycerol. Winemakers tried to simulate this effect by stressing the yeast during fermentation. Treatments included adding small amount of SO2 constantly during fermentation, adding unfermented juice to wine (osmotic shock) and stressing the yeast by cooling it suddenly. Many winemakers (and some of the best) practised fermentation practices where the must was cooled to 10°C, allowed to rise to 15°, cooled quickly to 10°C, allowed to warm etc, to increase the amount of glycerol in the wine.

 All these techniques probably resulted in an increase in the glycerol concentration, but had no effect on quality resulting from the glycerol.

Louis Nel is the owner and winemaker of Louis wines in South Africa.

Glycerol: the myth

comments ( 3 )
March 31, 2010  posted by Karien O'Kennedy
As a fermentation consultant I have spoken to many winemakers form very large co-ops (5 million litre tanks in Spain) to very boutique wineries all around the world. I have visited wineries that are fully automated, state of the art and wineries using 100-year-old wooden vats with no cooling whatsoever. In the latter case one winery’s Sauvignon blanc, Chardonnay and Riesling all tasted the same. Now that is an achievement of note. Imagine the series of adjectives one has to come up with if you taste the wine with the winemaker: interesting, not familiar with this style, etc… During all these talks with winemakers I have come across certain myths surrounding the sales of wine yeasts. Glycerol is my favourite one.
 
Winemakers believe that some yeasts improve the mouthfeel of a wine because of high glycerol production. It is sold to them based on that trait. I don’t blame them – it makes a nice story. Marketing people conducting wine tastings also LOVE pointing out the “high glycerol content” of wines. Well I am sorry to burst your bubble but unless the wine under discussion is a natural sweet or a noble late harvest, it is not the viscosity of glycerol that is responsible for the mouthfeel. Glycerol is a colourless, aroma less “alcohol” that is viscous in nature. It has a sweet taste. I know this because I dip my baby’s dummy in it and then she sucks it like Maggie Simpson. In concentrations higher than 5.2 g/L in wine it can contribute to the “sweetness” of a wine. Wine yeasts produce between 5 – 14 g/L in dry wines. It is not possible for the human palate to distinguish between glycerol concentrations in this range. A concentration of 25.8 g/L of glycerol is needed to have an effect on the viscosity of a wine. Some Botrytis wines can have this concentration. There is also no relationship between the “tears” in a wine glass and the glycerol content of a wine.
 
So what does give mouthfeel? Alcohol content, polyphenol content, residual sugar, polysaccharide content, mannoproteins, certain esters etc. Glycerol is thus not responsible for mouthfeel, but does play a small contributing part due its “sweet” taste.  The amount of glycerol a yeast can produce during fermentation should therefore not be the deal clincher in choosing a certain strain.
 
For further reading see what Tim Patterson has to say in his article: Many roads to mouthfeel.

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