Analysis of peptide fraction from white wines

Must oxidation is a complex process involving multiple enzymatic transformations, including the oxidation of phenolics containing an ortho-diphenol function. The latter process has a primary influence on wine aroma characteristics and stability, due to the central role of ortho-diphenols in the non-enzymatic oxidative reactions taking place during winemaking and in finished wine. Although oxidation of must is traditionally avoided, in recent years its contribution to wine quality has been revisited, and in some cases improvements to wine aroma have been observed with the application of controlled must oxidation. Nowadays there is a great interest in the wine industry towards the identification of specific markers or patterns to characterize and classify the response of grape must to oxidation.

The aromas found in young Bordeaux red wines made with Merlot and Cabernet Sauvignon suggest a complex mixture of aromas of fresh red fruits such as cherry or blackberry for Merlot, and strawberry or blackcurrant for Cabernet Sauvignon. The aromas of these wines are closely linked with the maturity of the grapes. The climate change that has occurred during the last decade in Bordeaux has induced changes in the ripening conditions of grape berries. It is now widely admitted that over-ripening of the berries during hot and dry summers results in the development of characteristic flavors reminiscent of cooked fruits (fig, prune). The presence of these overriding odors found in both musts and young wines affects the quality and subtlety of the wine flavor and may shorten its shelf life.

A new process for vacuum evaporation was developed where evaporation takes place near the inner surface of a vortex produced by a rotor submerged in the liquid. Contrary to the state of the art the Vortex rotor process does not need a vacuum vessel but the rotating liquid creates a geometrically stable low pressure void surrounded by a vortex stabilized by the equilibrium between centrifugal forces and the pressure difference. First tests with water and sugar solutions at concentrations similar to grape must were conducted to verify the theoretical predictions, test the performance under different conditions and study the effect of various process parameters (Rösti et al 2015).

The assessment of red wine mouthfeel relies primarily on the sensory description of its tannic properties. This evaluation could be improved by gaining a better understanding of the physicochemical properties of these tannins. Hence, the objectives of the present study were threefold: (1) to gain an insight into the sensory properties of subpopulations of proanthocyanidic tannins of different molecular sizes obtained through several ultrafiltration steps, (2) to quantify the kinetics of haze formation of these proanthocyanidic tannins in a dynamic polyvinylpyrrolidone (PVP) precipitation test, (3) to determine whether a correlation exists between the sensory and the precipitation data.

Not only vintner’s decisions in the vineyard, but also winemaker’s choices of technology approaches in the cellar play a significant role in the final wine style and quality. Whereas traditional technologies within chosen terroir are quite well explored and thus somehow predictable, there is no proper knowledge available on possible outcomes in case of implementing novel, alternative winemaking strategies. To reveal their effects on wine aroma compounds and sensory characteristics, two alternative strategies
(cryoextraction or addition of whole grape berries during last stages of fermentation) were compared to classical Vipava valley winemaking approach as normally used for an autochthonous variety Zelen. After separate vinification and bottling, all the experimental wines were subjected to semiquantitative metabolic profiling of volatile compounds (VOCs) by means of GC/MS and were then also sensorialy evaluated by pre-trained panel.