WINETECH Technical Yearbook 2021

PRACTICAL IN THE CELLAR | DECEMBER 2021

IRRESPECTIVE OF ORIGIN, CULTIVAR, STYLE OR PRIZE winners, all wines share one common factor, namely alcoholic fermentation. The sugar present in the grapes must be converted to alcohol and carbon dioxide, which requires yeast. The yeast can be received with the grapes or it can be added as pure culture yeast. Louis Pasteur already confirmed the existence and role of yeast in alcoholic fermentation in 1863. Before his observation, yeast had already played a role and spontaneous fermentation was the primary source of fermentation. With the development of yeast technology, it became possible to determine the weak and strong points, opportunities and threats of spontaneous fermentation with a SWOT analysis. In order to do this, it is important to define natural yeast. Natural yeast originates from the grapes, cellar surfaces or atmosphere and can also be seen as wild or indigenous yeast. These yeasts will commence alcoholic fermentation spontaneously, which is usually applied without sulphur dioxide additions. The microflora of yeasts is very area bound and also differs between vintages. Uncertainty exists concerning the vintage influence, but the region, cultivar, vineyard age, viticultural practices, environment and climate all have an influence on the microflora. Species of Hanseniaspora , Candida , Pichia , Kloeckera ,

Metschnikowia , Brettanomyces and Saccharomyces , with the ability of alcoholic fermentation have been isolated from vineyards. The spontaneous fermentation of grape juice therefore consists of different populations of different yeast flora. Different species will thus play a decisive role at the different stages of alcoholic fermentation. The temperature and alcohol concentration will especially influence it. The fermentation will also not necessarily be executed by the yeasts occurring on the grapes, but can rather be executed by the Saccharomyces population of the cellar. The accepted pattern of a spontaneous fermentation is often that the non-S accharomyces species initiate the fermentation, but Saccharomyces yeasts complete it. It is however not necessarily the Saccharomyces cerevisiae species, used by the cellar for other fermentations. An inoculated fermentation is using a wet culture or dried yeast to initiate and complete the alcoholic fermentation. In most cases it is a yeast strain of the known alcohol resistant, Saccharomyces cerevisiae. It is generally known as wine yeast. As a result of its sunlight sensitivity, it does not occur much on grapes, but usually has big populations in cellars. The strong points of spontaneous fermen- tation are the complexity and structure, which it can impart to wine. It is also more

Inoculated yeast ensures a sound fermentation.

The advantages and disadvantages of spontaneous fermentation

CHARL THERON: Private Consultant KEYWORDS: Spontaneous fermentation management.

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