AN AWARD-winning young WA researcher is investigating how climate influences the effectiveness of the 'cold soak' technique on red wines.
Bunbury-based Department of Agriculture and Food wine and grape research officer Richard Fennessy is comparing shiraz, cabernet sauvignon and merlot from warm and cool wine regions to evaluate the effect that climate and variety have on the pre-fermentative cold maceration or 'cold soak' process.
Cold soak is a technique some winemakers apply to freshly pressed grape skins, seeds and pulp, known as 'must'.
The must is chilled to allow slower extraction of colour and flavour before yeast is added to begin fermentation, which Mr Fennessy says encourages a gentler extraction of polyphenols—chemical compounds that contribute to a wine's taste, colour and aroma.
"You get a softer extraction of compounds in an aqueous rather than an alcoholic solution and those compounds tend to be polyphenols and aroma precursors," he says.
'Blind' taste test considers varieties
A panel of nine winemakers 'blind' tasted 24 wines from the Swan Valley and Mt Barker in December to assess colour, aroma and palate of the three varieties.
Mr Fennessy says the results were unexpected.
"The panel found the Swan Valley control shiraz were better quality...and there were no perceived differences between the cool climate shiraz," he says.
"The hot climate cabernet sauvignon was the polar opposite—the cold soak greatly benefited the cabernet quality, in particular a huge improvement in colour, while the Mt Barker cabernet sauvignon cold soak wines showed a higher intensity of dark berry aromas."
Mr Fennessy says merlot showed the most dramatic difference between treatment and climate.
"The Swan Valley control merlot had a greater intensity in colour and the sensory panel interestingly described the Mt Barker merlot as the same quality but stylistically different," he says.
Wine's individual imprint analysed
The wines were also chemically analysed at the Australian Wine Research Institute in South Australia to create a 'fingerprint' from the presence of 18 aromatic compounds.
"Qualitative analysis of volatile compounds by gas chromatography-mass spectrometry was undertaken on all wines," Mr Fennessy says.
"This non-targeted profiling technique discriminates samples based on their metabolic profile specific to a range of 18 volatile fermentation-derived compounds.
"That profile allow us to discriminate between treatments; we can compare those profiles against the different treatment between region and variety."
A second sensory panel assessment was conducted in July to evaluate differences in wine quality after six months in the bottle.
Mr Fennessy anticipates the findings will be finalised this month.