Mixed fermentations to reduce ethanol content in wine

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The aim of this project was to investigate the possibility of doing co-inoculation or sequential inoculation with Starmerella bacillaris (Candida zemplinina) and Saccharomyces cerevisiae in order to achieve lower alcohol wines.

Project layout
       Three S. bacillaris strains and two S. cerevisiae strains were used in the study.
       Fermentations were carried out in Barbera must;
       Pure fermentations (each strain on its own) as well as five inoculation strategies were carried out: co-inoculation of the two species and 7, 24, 41 and 48h after S. bacillaris inoculation;
       The best performing (in terms of alcohol reduction) couple and inoculation strategy were evaluated in 200 L must – 250.4 g/l sugar.

Results
       In pure fermentations S. bacillaris did not ferment to dryness (in 233.2 g/l Barbera must) and produced up to 12% alcohol, with only residual glucose – confirming its fructophilic nature;
       S. bacillaris produced slightly higher glycerol than S. cerevisiae and used slightly more sugar to produce 1% alcohol;
       The highest delay sequential inoculation in some cases affected S. cerevisiae growth;
       Acetic acid (still within normal range) and glycerol production increased with inoculation time delay;
       Laboratory scale fermentations demonstrated an up to 0.7% alcohol reduction.

Significance of the study
Only a 0.7% reduction in alcohol was achieved, which is similar to what has been achieved by other microbial alcohol reduction strategies. However, the fructophilic nature of S. bacillaris is very interesting and could potentially lower the incidence of stuck fermentations when mixed fermentations are used. This research focussed on five strains only. Further studies are needed with a wider range of strains and combinations, as well as inoculation strategies, in order to explore possibilities.

Reference
Vasileios Englezos, Kalliopi Rantsiou, Francesco Cravero, Fabrizio Torchio, Anne Ortiz-Julien, Vincenzo Gerbi, Luca Rolle, Luca Cocolin, 2016. Starmerella bacillaris and Saccharomyces cerevisiae mixed fermentations to reduce ethanol content in wine. Applied Microbiology and Biotechnology, Vol 100:12, pp 5515–5526


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