A new study has questioned standard thinking about the effects of dissolved carbon dioxide (C02) on sweetness, bitterness and astringency in still white and red wines.
The findings of the study – funded by Wine Australia and believed to be the first of its type on the taste and textural effects of dissolved CO2 at levels found in still wine – took its research investigators by surprise.
‘The findings were completely the opposite of what we expected’, said Dr Richard Gawel, Research Scientist at the Australian Wine Research Institute (AWRI).
Dissolved CO2 is a standard feature of all still wines, and excessive or insufficient levels in wine can have significant quality implications.
However, until now the impact of the dissolved CO2 on wine taste and texture has been unknown, as all research into the sensory effects of dissolved CO2 have involved levels more typical of sparkling or semi-sparkling (frizzante style) beverages.
In this study, a range of dissolved CO2 levels in Chardonnay, Viognier, Shiraz and Cabernet Sauvignon wines were produced by blending carbonated and nitrogen-sparged versions of the same wine. The wines were then re-bottled and re-sealed under screwcap.
‘The pH, alcohol, and (in the case of red wines) tannin levels of the wines were also varied in combination with dissolved CO2, as these matrix components are known to be primary drivers of mouth-feel in wine’, explained Dr Gawel.
The wines were tasted in conditions that reflected typical wine consumption – 150 mL pours into ‘restaurant’ style glasses and served chilled for whites and at room temperature for reds. Dissolved CO2 concentrations of the wine in the glass were then simultaneously measured using a modified ‘orbisphere’ system that took parallel measurements of dissolved CO2 from replicate wine glasses while the wines were being tasted by a trained sensory panel.
The study found that higher levels of dissolved CO2 consistently enhanced sweetness and reduced bitterness in both red and white wines and reduced the perception of astringency.
Dissolved CO2 levels did not consistently influence the perception of acidity, or the mouth-feel characteristics of perceived viscosity/fullness, or palate warmth due to alcohol.
‘We also found that pouring a wine into a glass results in a significant loss in dissolved CO2 compared with that measured in-bottle’, Dr Gawel said. Dissolved CO2 further decreased during the time in which a wine is typically consumed.
‘In total, up to 45 per cent losses in dissolved CO2 were observed from the beginning of pouring to when a wine may be consumed.’
Dr Gawel said he and the team were surprised by the findings.
‘The standard way of thinking is that increasing dissolved CO2 will make the wine taste more acidic and therefore less sweet and less bitter due to taste masking. Higher acidity from dissolved CO2 would also be expected to enhance astringency. In all cases we found the opposite of what was expected.’
‘We also expected that levels of dissolved CO2 resulting in a ‘spritz’ sensation would affect the perception of alcohol ‘warmth’ and perceived viscosity, as a single family of oral receptors are thought responsible for tactile and irritation perception in the mouth. But we didn’t see that either.’
Dr Gawel said the findings of the study could be helpful for future winemaking practice.
‘Achieving the correct balance in the taste and texture of wine is a crucial aspect of wines’ overall quality. This research gives guidance to winemakers as to how to factor in the effect of dissolved CO2 into the balance ‘equation’.’