Overview

High alcohol content has several important consequences:  wine flavour is often compromised; costs are inflated in countries where taxes are levied according to ethanol content; and excessive consumption of alcohol is associated with health issues. 

The Big Picture - Response and Responsibility

The wine industry is developing and evaluating strategies to reduce the alcohol/ethanol content of wine without compromising quality.   Harvesting grapes before they reach maturity, when sugar concentration in the berries is low, leads to wines with lower alcohol content.  However, this can compromise the full-bodied character and ripe fruit flavours that are desirable in many wines. Removal of sugar from must before fermentation will similarly lead to less ethanol production but this approach adds to production costs.  A third strategy is to remove alcohol from wine following fermentation (Spinning), but this approach also adds to the production costs and has the potential to affect wine flavour.

Alternative Solutions

An alternative strategy is to modify the fermentation process so that products other than less ethanol is produced from some of the grape sugars:  in other words, persuade wine yeast to make less alcohol.  Some yeast strains that have lower fermentation efficiencies have been identified but such yeasts typically alter the sensory properties of wine or are prone to other fermentation difficulties.  Researchers at The Australian Wine Research Institute (AWRI) are attempting to generate novel Saccharomyces cerevisiae wine yeast strains to redirect sugar metabolism to make less ethanol, whilst retaining the ability to make high quality wine.

Two approaches are being used to achieve this end.  One uses traditional breeding and selection techniques that will generate low-ethanol wine yeast variants and once developed these will be suitable for immediate adoption by the wine sector.   The second approach involves the generation of Genetically Modified (GM) research yeasts that divert sugar metabolism away from ethanol production.  While GM yeasts are not used or trialled for commercial production in Australia at this time, knowledge gained from this work can be used to better inform researchers what is possible in wine yeasts, and help develop improved strategies for generating suitable wine yeasts using traditional ‘breeding’ approaches in a targeted manner.

GM and Non-GM Reviewed

The GM approach builds on experimental work performed in several laboratories around the world which is mainly based on the following strategies: in one of these the modified yeast is engineered to convert sugars in grape must into metabolites that cannot be fermented, thereby rendering it ‘unavailable’ for ethanol production. 

The second strategy aims to enable wine yeast to divert some of its metabolites away from ethanol production, thereby generating different end-products.

The immediate challenge for the wine sector is to make ‘low-alcohol producing yeasts’ using traditional breeding and selection processes that are acceptable to the consumer and which can be adopted by winemakers.  Considerable commercial advantage will benefit the category or country which delivers the successful outcome first.

Crates

A Case In Point - Dr Tony Jordan, CEO and winemaker of Cape Mentelle and Domaine Chandon

“Winemakers are addressing the higher alcohol issue, and yes it’s to do with the health question, but more so it‘s purely and simply to do with what is the optimum balance for the wine. Technology has rapidly improved viticultural knowledge, just in the last 20 years. In adopting new canopy management techniques we have produced a virtual sugar factory in the vine. Perhaps we should also be looking at ways to reverse that and still get ripe tannins and fruit flavours?”

“There are several ways of making lower alcohol wines in the winery, from simple dilution through to de-alcoholising using spinning cone technology. Reverse osmosis followed by osmotic perstraction technology is a particularly good method. Reverse osmosis removes alcohol and water and then the osmotic perstraction separates the alcohol and water and you just take the water stream and add it back.”

“The day we allow genetically modified material into the winery is the day we might as well become Coca-Cola. That’s definitely the beginning of the end, it’s not terroir-based technology. I believe we need to be a bit atechnical here and wait for traditional selection techniques to come through. Some people say that if we don’t explore GM then the wine industry will be left behind – well, so be it!”

Summary

The Australian wine sector is responding to the challenge of producing rich and expressive wines that retain their positive attributes while minimising the potential for excessive alcohol.  Whilst research is looking into the benefits gained by development of genetically modified yeasts, use of such yeasts is not endorsed by the Australian wine industry and unlikely to occur in Australian wine making practice in the foreseeable future.  Targetted traditional breeding of yeasts that facilitate lower alcohol levels will deliver beneficial outcomes for producers and wine consumers.

Glossary

Alcohol, Genetically Modified, Grape Must, Fermentation, Ethanol, Metabolites, Saccharomyces cerevisiae, Spinning, Yeast strains, perstraction

Acknowledgements

This item has been written based on an extract of an article which appeared in ANZWIJ July 03 The connection between yeast and alcohol reduction in wine (authored by Miguel de Barros Lopes, Jeff Eglinton, Paul Henschke, Peter Høj and Isak Pretorius), a complete copy of this article may be ordered from Winetitles by visiting info@winetitles.com.au