WINETECH Technical Yearbook 2020

The impact of sulphur dioxide additions at crush on wine yeasts, bacteria and sensory attributes

on the wine yeast, bacteria and sensory attributes. In 2014 Canadian research was executed with Pinot gris to ascertain this. Three different levels of sulphur dioxide, namely 0, 20 and 40 mg/L respectively, were compared. The traditional winemaking analyses of temperature, residual sugar, pH, volatile acidity and total acid were done after fermentation and microbial analyses were applied to identify yeasts and bacteria. After completion of the alcoholic fermentation, the wines were racked and bottled for the blind sensory evaluation by a panel of 10 trained members. The chemical composition of the different levels of sulphur dioxide additions was very similar. The bacteria community was also not influenced by the different levels and did not vary during the different fermentation stages. Enterococcus bacteria represented about 70% of the bacteria population, followed by 15% of a Bacillaceae bacteria. Both are lactic acid bacteria, which are commonly identified in wine fermentations. The traditional Oenococcus , Lactobacillus and Leuconostoc species did however occur in very low populations. This can possibly be attributed to the low pH (3,35-3,27) and the sulphur dioxide additions where applicable. Bacteria are sensitive to both factors. The fungal community was however significantly influenced by the sulphur dioxide additions. After completion of the cold settling of juice, the communities

DECEMBER 2020

CHARL THERON: Private consultant KEYWORDS: Sulphur dioxide additions, wine sensory attributes

Sulphur dioxide is probably the most common additive during winemaking. As result of its anti-microbial and anti- oxidative properties, it is unique and no substitute could yet be found to replace it. Increasingly more consumers push the wine industry to limit the additives during winemaking. Due to its potential health risks, sulphur dioxide is one of them. The addition of sulphur dioxide at the crushing of grapes and just before bottling is probably the most common stage of addition. Even if no sulphur dioxide is added during winemaking, some yeasts form small quantities thereof during fermentation and there is consequently not a sulphur-free wine. Grape juice contains different yeast species of which

Saccharomyces cerevisiae is usually dominant during alcoholic fermentation. It is however a cellar resident, which is rarely found on healthy grapes in the vineyard. It is also less sensitive to sulphur dioxide than the non- Saccharomyces species, which occur in the vineyard. A large variety of Saccharomyces cerevisiae species is commercially available, which can remain in cellars for a long time and dominate fermentations. Winemakers may however prefer to execute spontaneous fermentation with yeast occurring in the vineyards to express the terroir of the vineyard. They can also decide to decrease or limit the use of sulphur dioxide, but little research has been executed to determine the influence of such a decrease at crush

Sulphur dioxide adjustments can be done in liquid form by means of a SO 2 cylinder.

WINETECH TECHNICAL YEARBOOK 2020 176