Better wine through chemistry

Every time you open a bottle of sparkling wine, you are uncorking a bit of mystery. There is still a lot we don’t know about the chemistry of sparkling wine and how that chemistry is achieved, according to Fiona Kerslake at the University of Tasmania.

In a joint venture funded by Wine Australia, she and her colleagues at the Tasmanian Institute of Agriculture have teamed up with winemakers to develop a way to analyse the chemical composition of sparkling wine more rapidly, and perhaps even to speed up production.

The complex puzzle begins on the vine, she explains. Soil, climate, irrigation, fertilisation and pruning each influence the outcome, as do winemaking practices from juice-extraction techniques through to storage temperature.

However, Kerslake says: “Knowledge of the chemistry of sparkling wines is quite limited, and so are the ways we can potentially analyse sparkling wines.”

In red wine, many important chemical compounds are large and have colour, so they can be studied by measuring how the wine absorbs visible light. However, many compounds in white and sparkling wines are smaller and colourless, making them difficult to examine, Kerslake says.

To address this, Kerslake has been analysing juice destined for sparkling wine with visible, infrared and ultraviolet light. This process, done as the grapes are pressed, is letting wine makers understand their wine at the molecular level.

Long maturation times are also a challenge for wineries racing to keep up with high demand, says Kerslake: “You have to be pretty patient if you’re into sparkling wine.”

First, juice is fermented to create a still wine. Then yeast and sugar are added. As yeast consumes sugar, alcohol is produced along with bubble-making carbon dioxide. But something else is going on, too.

Around three months after this secondary fermentation begins, the yeast cells begin to release compounds associated with desirable flavours, such as toasty, nutty or sweet notes. This process usually takes around 18 months.

Kerslake wondered if preemptively damaging some of the yeast would trigger early release of desirable compounds.

To find out, she and PhD student Gail Gnoinski added damaged yeast to still wine, and preliminary results suggest it is gaining the characteristics of slightly older wine.

Meanwhile, they are also trying to figure out exactly what happens to yeast during fermentation.

“There’s a bit of a question around whether the yeast cells actually die or whether they just go to sleep or… leak,” says Kerslake.

So Gnoinski is opening wine at different stages and examining the yeast under the microscope. Her findings could reveal which cellular mechanisms are active, and help to identify the molecular pathways responsible for a nice glass of bubbly.