Metabolomics of Red Wines Aged Traditionally, with Chips or Staves.

Traditionally and alternatively aged wines' odour activity values (OAVs) are investigated to differentiate and highlight the differences between the selected methods. An analysis of the volatile aroma compounds of wines derived from ageing in barrels, oak chips, and staves was performed using stir bar sorptive extraction chromatography-mass spectroscopy (SBSE-GC-MS). The results showed that alcohols, esters, and oak compounds were the main contributors to aroma, and their OAVs were higher in the stave samples after 3 months than in the samples from the other two systems of ageing. Furthermore, wines aged with staves have stronger fruity, spiced, and woody aromas, while samples aged in barrels present more chemistry-driven, floral, caramelly, and creamy aromas. The staves-medium plus toast (SMPT at 3 months > 225) and chips-medium plus toast (CMPT at 3 months > 170) showed the highest levels of aromatic series, suggesting that alternative systems provided more powerful aromas than traditional systems, such as barrels-medium plus toast (BMPT at 3 months > 150). A principal component analysis (PCA), orthogonal partial least squares (OPLS) analysis, and cluster analysis allowed for a clear differentiation to be made between red wines according to ageing systems and ageing times. The odour activity values fingerprint in winemaking is a feasible approach to characterise and distinguish wines. Moreover, OAVs provide important information on the effects of production methods on wine quality and aroma profile.

Sweet wine production by two osmotolerant Saccharomyces cerevisiae strains.

The use of Saccharomyces cerevisiae to produce sweet wine is difficult because yeast is affected by a hyperosmotic stress due to the high sugar concentrations in the fermenting must. One possible alternative could be the coimmobilization of the osmotolerant yeast strains S. cerevisiae X4 and X5 on Penicillium chrysogenum strain H3 (GRAS) for the partial fermentation of raisin musts. This immobilized has been, namely, as yeast biocapsules. Traditional sweet wine (that is, without fermentation of the must) and must partially fermented by free yeast cells were also used for comparison. Partially fermented sweet wines showed higher concentration of the volatile compounds than traditionally produced wines. The wines obtained by immobilized yeast cells reached minor concentrations of major alcohols than wines by free cells. The consumption of specific nitrogen compounds was dependent on yeast strain and the cellular immobilization. A principal component analysis shows that the compounds related to the response to osmotic stress (glycerol, acetaldehyde, acetoin, and butanediol) clearly differentiate the wines obtained with free yeasts but not the wines obtained with immobilized yeasts.