VINEYARD PRACTICES INFLUENCE MICROBIAL DIVERSITY IN SPONTANEOUS FERMENTATIONS

by Karien O'Kennedy - 05 Apr 2016

PRESS RELEASE

By Karien O’Kennedy

2 November 2015

For immediate release

 

VINEYARD PRACTICES INFLUENCE MICROBIAL DIVERSITY IN SPONTANEOUS FERMENTATIONS

STELLENBOSCH - Dr Evodia Setati and her team at the Institute for Wine Biotechnology, Stellenbosch University, have found distinct differences in the diversity of yeast populations in three neighbouring Cabernet Sauvignon vineyards cultivated using different agronomic practices. The researchers found that some of these yeast species may occur in relatively large populations during fermentation and may consequently make a significant contribution to the wine’s eventual sensorial quality.

The investigations were conducted in 2012 and 2013 on three Cabernet Sauvignon vineyards adjacent to each other in the Polkadraai, Stellenbosch area. Management of the three vineyards differs, namely biodynamic, IPW (integrated production of wine – practices according to environmentally friendly guidelines) and conventional (generally more chemical treatments used). All three vineyards are more or less the same age and the same trellis system was used for all three. Fermentation kinetics and yeast population dynamics were monitored from the start to the end of fermentation. The following findings emerged:

  • Different viticultural cultivation practices, as well as different vintages, resulted in large differences in microbe population. There were also large differences within the same vineyard.
  • The most commonly found microbes on the grapes of the three vineyards were the oxidative (require oxygen to grow) yeasts: Aureobasidium, Cryptococcus and Rhodotorula. They disappeard as soon as fermentation began.
  • Before fermentation Saccharomyces cerevisiae, the main fermentative wine yeast, could only be isolated from the juice deriving from the biodynamic vineyard.
  • The must from the biodynamic vineyard displayed the biggest microbial population as well as microbial diversity.
  • Each must comprised different combinations of non-Saccharomyces yeasts with significantly different assortments of dominant species that included Starmerella, Lachancea, Hanseniaspora, Candida and Wickerhamomyces species.
  • In all three fermentations Saccharomyces cerevisiae was the dominant yeast from the middle of fermentation onwards.
  • Non-Saccharomyces yeasts with known potential to affect wine’s sensory quality persisted in high numbers for a significant part of the fermentation. None of them appeared to affect the growth of S. cerevisiae.
  • Glucose and fructose consumption rates indicated active participation from both glucophilic and fructophilic yeasts (such as Starmerella bacillaris / Candida zemplinina). The researchers conculded that the manner in which we cultivate vineyards is one way to manipulate the grape must microbial population. “Knowledge of the initial microbiome can be an important future management tool for winemakers. It can allow them to enhance or suppress dominant species in order to achieve a positive spontaneous fermentation outcome” according to Dr. Setati. Spontaneous fermentations, as opposed to inoculating with commercial starter cultures, are winning favour again worldwide in the strive for authenticity, terroir expression, minimising one’s carbon footprint and sustainability. The South African wine industry has the major advantage of an incredible diversity of soil and climate since most of the wine industry is located in the Cape Floral Kingdom, a UNESCO world heritage site. It is the smallest but richest in the world and contain more plant species than the whole northerm hemisphere. Research into the uniquely South African microbiome is ongoing.

The projects were funded by Winetech and the National Research Foundation.

The Institute for Wine Biotechnology (IWBT), part of the Department of Viticulture and Oenology, was established at Stellenbosch University in 1995. The IWBT is an internationally recognised postgraduate training and research institute offering visionary training and innovative research to support the South African wine and grapevine industries

Bagheri, B., Bauer F. And M.E. Setati*. 2015. The diversity and dinamics of indigenous yeast communities in grape must from vineyards employing different agronomic practices and their influence on wine fermentation. S. Afr. J. Eno. Vit. Vol. 36, No.2

 

Corresponding author: Dr. Evodia Setati (setati@sun.ac.za)

Press officer: Karien O’Kennedy (kennedy@sun.ac.za)

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