Searching for indigenous yeasts to create tastier wine
Yeasts are everywhere. These blessed creatures are the building blocks for a party and they let us enjoy mouth-watering food and drinks, writes University of Adelaide scientist Natalia Caliani.
Many of our favourite treats are produced by microscopic workers known as yeast.
Some of us enjoy baking a crunchy loaf of sourdough; while others enjoy home-brew and experimenting with different malts, fruits or hops to get a perfect beer. And that bottle of Barossa Shiraz you’re enjoying with your friends... bingo, yeast were also involved to produce it!
Fermentation processes of baking, brewing and winemaking rely on different Saccharomyces yeast which produce ethanol and carbon dioxide (CO2) as the main metabolites.
For example, this CO2 is responsible for rising our bread dough - but don’t worry, the ethanol produced evaporates during the baking process.
What is yeast?
Yeasts are single-celled micro-fungi, and there are over 1000 different species. The baker’s yeast (Saccharomyces cerevisiae) is the most commonly used in food and beverage production. If you have ever made bread, beer or wine at home it is likely you used a little packet of Saccharomyces cerevisiae yeast.
Even commercial winemakers can go to specialist manufacturers to buy yeast specifically selected for winemaking.
What about the other 1000 species of yeast? While Saccharomyces is the most common, there is an increasing number of other species being used in winemaking.
Some of these are indigenous or native yeasts which have been found on, and isolated from, grapevines, bunches and winery equipment. They have been found to be useful in winemaking.
These non-Saccharomyces yeast have fancy-sounding species names like Torulaspora delbrueckii, Lachancea thermotolerans, Hanseniaspora uvarum, and the list keeps going.
When creating wine, some winemakers prefer to leave the grape juice and let indigenous or native yeast ferment the juice into wine without adding any packaged yeast.
The indigenous yeast, usually non-Saccharomyces species, come from the grapes in the vineyard and when these grapes are crushed, they are transferred to the juice. Some winemakers call the this ‘wild’ wine.
An example of this is the Wild Ferments range from the Yalumba winery, produced by University of Adelaide alumni Louisa Rose.
Interestingly, research shows that non-Saccharomyces can be an innovative tool for winemakers willing to produce distinctive wines with richer aroma, mouthfeel, texture and wine length.
There can be some downsides to indigenous yeast though, as they may not be able to complete the job - fermentation - as well as Saccharomyces.
My research at the University of Adelaide’s School of Agriculture, Food and Wine involves working with indigenous, non-Saccharomyces yeast isolated from vineyards to screen them for useful winemaking characteristics including:
- Ethanol resistance: most wines are fermented until all the sugars in the fruit have been consumed and transformed into ethanol. As ethanol is a toxic substance for yeast, some struggle to remain alive as fermentation progresses and ethanol levels rise.
- Sulphur dioxide resistance: Sulphur is used as the main antimicrobial and antioxidant agent in winemaking and can be toxic to yeast at high concentrations. However, we need our new yeast to resist at least the concentrations used during fermentation to protect the wine.
- Nutritional requirements: if their nitrogen nutritional needs are low, we know they will finish fermentation without the need for extra nitrogen to be added.
- Desirable aroma compound production: we all like finding those beautiful floral or fruity aromas in wine, right?
I hope my work will find a new winemaking superstar to add to the winemaker’s arsenal of yeast to produce more interesting and delicious wines in the years to come.
About the author: Natalia Caliani
The growing interest in more interesting and innovative wine production has led us to investigate wild yeast populations found on grape surfaces. These species known as non-Saccharomyces, seem very promising as they can contribute to improving aromas and global perception of wine.
However, there are still many aspects of their metabolism that we do not know. My research aims to investigate their resistance to different wine stressors such as fungicides, ethanol and sulphur dioxide; and then determine how they could be used to benefit the wine industry.
Natalia acknowledges her PhD supervisors, the Australian Research Council Training Centre for Innovative Wine Production, the centre’s industry partners and Yalumba winery for their contributions to the project.