New yeast varieties could help improve the clarity and appearance of white wine, writes Ms Thulile Ndlovu, a doctoral student in Wine Biotechnology at Stellenbosch University (SU), in the November edition of WineLand Magazine.

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Mannoproteins in the research spotlight

Yeast strains discovered during Ndlovu’s study have the potential to protect against wine haze. These strains can be used as starter cultures for wine making or as clarifying agents to be added at the end of alcoholic fermentation. As different wines have different wine styles with regard to aroma, flavour and mouth feel, these strains cannot be used as starter cultures for all the different wine styles.

Mannoproteins are released during the fermentation of grapes, to help reduce haziness. However, these mannoproteins are, according to Ndlovu, released in such low concentrations by the most commonly used commercial wine yeasts strains, that they do not have any significant impact on the quality and clarity of wine.

If the use of genetically engineered yeast could be permitted in wine making, these strains can be further genetically modified to protect against haze and to improve the quality of wine.

Although genetically modified strains with positive wine attributes already exist, they have not been commercialized because of the negative reactions of some consumers to genetically modified wine.

According to Ndlovu, the use of genetic modification is a cost-effective, targeted and simple way to improve wine clarity. New wines with awesome flavours and mouth feel can be produced using genetically modified yeast. This will definitely reduce the expenditure costs for the wine industry and consequently the price of wine.

Moreover, it will limit the use of fining agents such as egg whites, bentonite, casein derived from milk, gelatine and isinglass obtained from bladders of fish to address wine haze. These agents are added before bottling to adsorb insoluble particles such as proteins and to stabilise compounds that may form wine haze. Bentonite is by far the most commonly used agent, but results in loss of wine volume, flavour and aroma compounds. It is also non-recyclable.

Applying these agents is labour intensive and costly to the wine industry.  Besides their negative impact on wine quality, most clarifying agents, especially those derived from animal or plant products, may cause human allergies, and also pollute the environment.

The removal of yeasts during the racking process is likely to leave no trace of yeast DNA in the wine. This eliminates any risk to human health.

Developing an alternative and cost-effective method to remove the grape proteins from wine thought to cause wine haze formation would benefit the wine maker as well as the wine industry.

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