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Non-Saccharomyces yeasts are prevalent at the onset of grape must fermentations and can have a significant influence on the final wine product. In contrast to Saccharomyces cerevisiae, the biosynthetic pathways leading to aroma compound formation in these non-conventional yeasts, in particular those that are derived from amino acid metabolism, remains largely unexplored. Within a synthetic must environment, we investigated the amino acid utilization of four species (Hanseniaspora uvarum, Hanseniaspora osmophila, Zygosaccharomyces rouxii, Starmerella bacillaris) and S. cerevisiae. We report on the differential uptake preferences for amino acids with H. uvarum displaying the most rapid uptake of most amino acids. To investigate the fate of amino acids and their direct contribution to aroma synthesis in H. uvarum, H. osmophila and Z. rouxii, musts were supplemented with single amino acids. Aroma profiling undertaken after three days showed the synthesis of specific aroma compounds by the respective yeast was dependent on the specific amino acid supplementation. H. osmophila showed similarities to S. cerevisiae in both amino acid uptake and the synthesis of aroma compounds depending on the nitrogen sources. This study shows how the uptake of specific amino acids contributes to the synthesis of aroma compounds in wine fermentations using different non-Saccharomyces yeasts. [ABSTRACT FROM AUTHOR]

The site specific influence on wine (Terroir) is an often by wine producers, consumers and scientists discussed topic in the world of wine. A study on grapes and (spontaneous) fermentations from six different vineyards was done to investigate the biodiversity of yeasts and to answer the question if there is a terroir of yeast and how it could be influenced. Randomly isolated yeasts were identified by FTIR-spectroscopy and molecular methods on species and strain level. Vineyard specific yeast floras would be observed but they are not such important as expected. Only a few overlapping strain patterns would be identified during both vintages. The yeast flora of the winery had a huge impact on the spontaneous fermentations, but is not really constant and influenced by different factors from outside.

In this paper, we study model predictive control (MPC) of the cooling process during wine fermentation. A strategy to solve nonlinear control problems with changing model parameters and changes in the states is presented. The parameters and states determining the fermentation dynamics are regularly estimated from measurements and the optimal cooling profile is computed and if necessary adjusted. The process of wine fermentation is described by a modified version of the novel model including a death phase for yeast and the influence of oxygen on the process published in Borzi et al. (2014). This modification guarantees that nutrients can still be consumed in an anaerobic environment. The numerical results regarding the control inputs and the development of the substrates and the product for an industrial controller and for this MPC controller are compared. It arises that the usage of this MPC cooling strategy results in considerable savings for the energy consumption in the process of wine fermentation. [ABSTRACT FROM AUTHOR]