Less alcohol, more flavour with special yeast

Friday, 17 January, 2014

While more alcohol in your wine doesn’t necessarily sound like a bad thing, the gradual increase of the alcohol content of Australian wines over the last decade is concerning to some. Alcohol levels have crept up to around 12.5% - and even as high as 15% - which some wine buffs say threatens the flavour and character of wine.

In addition, increased alcohol content in wine raises concerns around public health and taxes. (In some countries, tax is imposed based on alcohol content.)

A team of researchers at the Australian Wine Research Institute (AWRI) has identified a strain of yeast that produces a lower level of alcohol, while preserving the flavour. Their research is due to be published in the March 2014 issue of Applied and Environmental Microbiology.

The researchers began by systematically screening non-Sacchromyces yeasts, evaluating 50 isolates from 40 species and 24 genera, assessing them for their capacity to produce wine with reduced ethanol concentration. They found the most successful of these yeasts was Metschnikowia pulcherrima AWRI1149.

The Metschnikowia was set to work on Chardonnay and Shiraz musts. Once it had consumed 50% of the sugar, Sacchromyces cerevisiae were added to the mix to complete the process. This ‘sequential inoculation’ reduced the alcohol content in Shiraz from 15 to 13.4%. The effect was less pronounced in Chardonnay, but still significant.

“The reduction isn’t all that great, but it’s in the right direction, and with more work, they might get that even lower, perhaps by letting the non-Saccharomyces yeast go longer before they throw in the Saccharomyces,” commented Alan Bakalinsky of Oregon State University. (Bakalinsky was not involved in the research.)

According to Louisa Rose, a director of the AWRI, this reduction in alcohol will be of great benefit to the industry. “It is using techniques - sequential fermentation - that can easily be used in the winery on a commercial scale,” Rose said.

The rise in alcohol content has been attributed to the later harvesting of red wine grapes. This allows the tannins to soften and, in some varieties, minimises the presence of off-flavours such as methoxypyrazines. However, the increased alcohol content reduces aroma and flavour intensity, as well as otherwise impairing the oenological experience, the AWRI says.

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