Characterization of commercial enological tannins and its effect on human saliva diffusion

Chemical studies aiming at assessing how a wine reacts towards oxidation usually focus on the characterization of wine constituents, such as polyphenols, or oxidation products. As an alternative, the key oxidation intermediate hydrogen peroxide H2O2 has never been quantified, although it plays a pivotal role in wine oxidation. H2O2 is obtained from molecular oxygen as the result of a first cascade of oxidation reactions involving metal ions and polyphenols. The produced H2O2 then reacts in a second cascade of oxidation to produce reactive hydroxyl radicals that can attack almost any chemical substrate in wine.

For characterization, sensory designing and authentication rapid analytical technologies have become available. Some, like Proton Transfer Reaction Mass Spectrometry allow a rapid spectrum of the volatile compounds of wines. Combined with chemometrics wines can be characterized. The same approach can be used to calculate the results of virtual mixtures and allow formulation of constant quality blends. Other new techniques and portable devices based on spectroscopy allow measurements on production sites and in grocery stores, even for the smart consumer. We will present some examples of the application of these techniques for authentication of wines, both in the laboratory and on site.

Light-struck taste is a defect prevalent in white wines bottled in clear glass light-exposed for a considerable amount of time leading to a loss of color and appearance of sulfur-like odors. The reaction involves riboflavin (RF), a highly photosensitive compound that undergoes to intermolecular photoreduction by the uptake of two electron equivalents from an external donor, the methionine. The reaction includes different steps forming methional which is extremely unstable and decomposes to methane thiol and acrolein. The reaction of two molecules of methane thiol yields dimethyl disulfide. Methane thiol is highly volatile, has a low perception threshold (2 to 10 µg/L in wine) and confers aroma-like rotten eggs or cabbage.

Wooden barrels have been the preferred method for oak maturation for wines, but the use of alternative oak products, such as staves and oak chips have increased in South Africa due to lower production costs. This study investigated the effect of different oak products used during fermentation and ageing on the sensory profile, degree of liking and perceived quality of a South African Chenin blanc wine. The different wine treatments included an unoaked tank control wine, wines matured in 5th fill barrels, wines matured in new barrels from three different cooperages, and wines matured in 5th fill barrels with stave inserts from two different cooperages.

The effects of anthropogenic activities on vineyard (different plant protections) and in winery
(pressing/clarification step, addition of sulfur dioxide) on fungal populations from grape to wine were studied. The studied anthropogenic activities modify the fungal diversity. Thus, lower biodiversity of grapes from organic modality was measured for the three vintages considered compared to biodiversity from ecophyto modality and conventional modality. The pressing / clarification steps strongly modify fungal populations and the influence of the winery flora is highlighted.