Finding Beauty in the Yeast

If sugar is the ‘Beauty’ in the fairy-tale of winemaking, yeast is the ‘Beast’ that transforms grape juice into wine by converting sugar into alcohol and aroma compounds

If sugar is the 'Beauty' in the fairy-tale of winemaking, yeast is the 'Beast' that transforms grape juice into wine by converting sugar into alcohol and aroma compounds.

The vineyard endows grapes with nature's beauty, but microorganisms involved in wine fermentation are predominantly found in the winery. Yeasts love sugars so when sweet, ripe grapes are brought into the winery, yeasts gobble up the grapes' natural sugars metabolising them into alcohol. This process is called alcoholic fermentation. According to Sam Harrop MW and Lallemand Australia's Dr Eveline Bartowsky, we should all learn to love the beast, for without yeast there would be no wine.

Speaking at a WineSPIT Master Class on fermentation and microbiology at MWM Wine School, Harrop and Dr Bartowsky told members of the Hong Kong and Greater China wine trade that understanding yeast is critical to winemaking because yeast selection can influence the style of a wine. In fact, if you used four different selected yeasts in the same grape juice, you would most likely have four distinctive wines. The wines would still respect the grape variety and the terroir - as yeast can't create flavour - but yeasts will take what the grapes have to offer, and transform them into

perceivable aroma compounds. Each yeast has a different metabolism and via its unique metabolism will transform the grapes' non-aromatic compounds into aromatic ones. Yeast helps winemakers interpret the desired characteristics of terroir and grape variety and expresses this in their wines. It also helps to control other aspects of winemaking, such as regulating microorganisms, including those that cause spoilage and wine faults.

Harrop said it is important for a winemaker at the top of his/her game to really understand which selected wine yeast can provide the characteristics the winemaker is seeking, not just generally assuming one size fits all.

"The best winemakers are like the best architects – with just the right amount of intervention, they must accept a certain level of control is vital if their wines are to show a true sense of place. They must strike a balance between methodology and intuition if nature is to be reflected in their work," he said.

All yeast is natural, and is part of the winemaking process, Dr Bartowsky clarified. Yeasts are selected from grape must and cultivated. These selected yeasts can impact wine technologically (less sulphur dioxide (SO2), for example) and winemakers can use different yeasts based on their wine conditions. Lallemand