The effect of Nitrogen and Sulphur foliar applications in hot climates

The chemical mechanisms involved in oxidation/reduction potential of wine during winemaking and aging are affecting its color, aroma and taste. Chemical oxidation is one of the major causes of development of off-flavors during ageing1. Thus, the chemical changes in wine during storage should be controlled to ensure the sensory quality of the product and avoid consumer rejection that will compromise the economic value of the product. The 1-hydroxyethyl radical has been recognized as the key radical intermediate in the oxidative reactions in wine2. Based on the kinetic study of POBN-1-hydroxyethyl spin adduct formation in wines initiated via the Fenton reaction, a novel tool was recently developed in our laboratory to quantify the resistance of wines against oxidation3.

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.

Barrel ageing is a crucial step in the wine process because it allows many changes to the wine as enrichment, colour stabilization, clarification and also a slow oxygenation. Effects of the oak barrel have to be known to prevent oxidation of the wine. The type of bung used during ageing is also a parameter to consider. Ageing sweet wines in barrel is a real challenge. These wines may need some oxygen at the beginning of ageing but they should be protected at the end of their maturation, to avoid oxidation.

Viura is a synonym for Macabeo and currently it is the most widely planted white grape variety in D.O.Ca. Rioja, with 3,569 ha, representing 84% of the white grape cultivated area. It is a generous-yielding grape, presenting low values of titratable acidity and with large and compact clusters which makes it susceptible to Botrytis cinerea. Thus, this variety not always satisfies the wine grower’s prospects. Nowadays, the available plant material is scarce, moreover, it was selected on the basis of other quality criteria, not currently requested.

Bases on oxoluminescence, we have developed an innovative device for measuring dissolved oxygen in wines in barrels without opening the bung. This system is directly inserted into the wood during the barrel elaboration and can be positioned at different locations of the barrel (the head, the hull …). During two successive vintages we have used this device notably to follow the oxygen dissolved of whites wines elaborated in barrels. This allowed us initially to monitor the oxygen levels of the harvest to bottling the whole elaboration process in barrels of white wines without using techniques of measurement suitable to modify the real values in wines (opening the bung to plunge an oximeter).