Holding a glass of wine by its stem, careful not to warm the liquid with body heat, you raise it to the light above your head. The bright, clear liquid is the shade of pale straw, informing you of its youth and pure character.
You bring your nose to the rim of the glass and lower it in, inhaling deeply. Its aroma is inviting and fresh, full of fruit with strong notes of apple and citrus.
As you finish inhaling, you begin to sense the more subtle hints woven into the complex mixture like mango, rose petal and an undertone of lime zest. The first drink allows for the playful acidity to tease your palate, creating a medley of crisp blossom flavours and a mineral backbone that lingers to a finish.
This is the experience of a 2009 Heggies Eden Valley Riesling. This vintage won a gold medal at the Royal Queensland Wine Show in 2009. The Eden Valley is just one of Australia’s 60 wine regions which supply the Australian people with table wines.
Creating the perfect wine experience is a huge industry in Australia.
Each Australian consumes 21.1 L of wine each year, on average. It is a $3.02 billion industry that employs 28,000 people.
Australia is fourth largest exporter of wines in the world and the 16th biggest wine drinking country. Due to its popularity as a household product, wine is the third most lucrative product to Australian agricultural exports behind meat and wheat.
But there is still a lot of uncertainty in the wine making process. Factors such as the amount of water available during the grape-growing season, the time the grapes are picked when ripening and the type of yeast used in the fermentation process can all affect the elusive qualities that winemakers try to draw out of the wines.
Researchers based at the Australian Wine Research Institute, the National Wine and Grape Industry Centre and the CSIRO are trying to reduce that uncertainty. One way is by sequencing the genomes of different yeasts and measuring their effects upon the developing characters in wine such as aroma and flavour.
“This research gives winemakers much more control over a process that is becoming increasingly challenging due to climate change and restricted availability of water,” said Vladimir Jiranek, Associate Professor in Oenology at the University of Adelaide.
Researchers believe wine aroma is dependent on volatile molecules and that many of these molecules are either enhanced or suppressed by the type of yeast used in the fermentation process.
A wine fermentation can become stuck or sluggish resulting in a failed vintage or poor quality wine. However, robust yeast strains are less likely to lead to this problem because of their resilience to harsher conditions.
“The problem is, some of the less robust yeast strains can produce magnificent wines,” said Paul Chambers, the Research Manager of Bioscience at The Australian Wine Research Institute (AWRI) in Urrbrae, South Australia.
Researchers are trying to understand how to make more stress tolerant yeasts so that greater quality wines can be made, researchers said. “Grape juice is a very inhospitable environment so yeast has to be able to handle a very stressful world,” said Chambers.
Most wine yeasts are from the species Saccharomyces cerevisiae but each strain has a different genetic composition that determines how robust it is and which flavours and aromas it will enhance in a wine, Chambers says.
But to discover which yeast strains enhance favourable aromas, researchers had to discover the identity of the molecules that contribute to wine.
To determine the identity of the aroma molecules that create fruity aromas David Jeffery, Senior Research Scientist from the AWRI, and his team screened small ferments by examining aroma compounds. The screening process required an instrument that separated aroma compounds based on their physical properties, such as boiling point.
Then the separated compound was sent to a port where an individual could sniff and describe the compound.
They discovered that the molecule rotundone is responsible for the pepper aroma in Shiraz. They also uncovered that sulphur-containing compounds known as thiols compose many of the fruit aromas in Sauvignon Blanc.
They made their results public, publishing the results in The Journal of Agricultural and Food Chemistry in 2008.
“This process utilises gas chromatography-olfactory which requires instrumental detection and human detection at the same time,” said Jeffery. And with definitive results from these experiments, the researchers are able to test exactly how these compounds are affected by different variables.
The variable that most noticeably impacts these aroma compounds is the type of yeast used in the fermentation process.
“Different yeasts can give vastly different wine aroma profiles so the choice of yeast can be crucial to arriving at a desired wine style,” Jeffery said.
Wine producers are in the business of creating interesting and complex wines that appeal to customers. In some cases, this means wines with fruity characters, says Chambers. To better understand how to achieve these fruity characteristics, researchers are trying to discern the origin of aromas during fermentation.
Researchers suspect that, in the evolution of yeast, alcohol production in fermentation was a selective advantage because it killed off competitors, and aroma production evolved to attract insects; a yeast’s survival depends on it being transported to new food sources, which researchers suggest may occur through insect transportation.
Because it is speculated by researchers that yeast evolved odour production capabilities to aide in its dispersal, its effects upon the concentration of aroma molecules in grape juice can be better understood.
Certain yeasts allow for aromas such as passion fruit to be released at different levels. Chambers and his team made a genetically modified yeast using an enzyme that they knew would release thiols, or sulphur compounds, which are responsible for fruity aromas when present in a small concentration.
“When this yeast was used to ferment juice from rather bland grapes that normally would not produce much aroma, it released a large concentration of thiols, resulting in a Sauvignon Blanc with an overpowering odour of passionfruit,” says Chambers.
This development, which was published in the journal Yeast, showed that yeast could influence the aromas in wine juice to a very large degree. “We aim to get yeast to massage grape juice in different ways, uncovering the potential tucked away in the juice,” said Chambers.
This chemical and biological research at the AWRI is combined in order to refine the product that winemakers produce.
Chemical research determines which molecular compounds there are in wine that influence aroma and biological testing determines how different strains of yeast effect those compounds in the fermentation process.
“We aim to create yeast strains for winemakers that will ensure fermentations proceed without a problem and at the same time creates quality wines,” says Chambers.
“We are also working on many other areas of wine aroma chemistry, such as the effect of eucalypt trees on wine aroma. This is a very interesting aspect of our work involving vineyard local environments with a truly Australian component,” says Jeffery.
“This approach [to research] is more informed because with the knowledge of what this wine chemistry consists of and how yeast affects that it is possible to make desired changes much more specifically,” says Jiranek.
Yeast manufactures that provide strains of yeast to winemakers are keen to identify and commercialise strains with novel properties to achieve specific flavour and quality outcomes.
Even as the knowledge and technology progresses, new challenges such as climate change will be harder to master. It is hard to say whether the art of making wine will ever become a science completely. It may be this quality of elusiveness which draws so many to the profession of winemaking and the drink it creates.