Unravel the underlying mechanisms of delaying ripening techniques in grapevine

Red wines constitute the majority of the wines produced in Bordeaux. All along the winemaking process, many microorganisms may develop in wine. A lot of them are useful but a common defect found in wine is linked to the development of Brettanomyces bruxellensis, a yeast that produces volatile phenols. These molecules are responsible for an unwanted sensorial defect described as similar to “horse sweat”, “burnt plastic” or “leather”. It has been shown that while some wines are very permissive and easily contaminated, others are pretty resistant to Brettanomyces development. However, common parameters such as pH, alcohol or sugars composition cannot fully explain the differences observed in wine permissiveness.

Polyphenolic compounds are considered to have a major impact on the quality of red wines. Sensory impact, such as astringency and bitterness, stems directly from tannin composition. Thenceforth, quick analytical measurement of phenolic compounds appears to be a real challenge for winemaking monitoring and process control. Many methods were developed to analyzed polyphenols in wine, but they are time-consuming and require chemistry skills and equipment, not suitable for a rapid routine analysis. A reliable and rapid method to obtain this kind of measurement is Fourier Transform Infrared (FTIR) spectroscopy.

The interactions among aromatic compounds and proteins is an important issue for the quality of foods and beverages. In wine, the loss of flavor after vinification is associated to bentonite treatment and this effect can be the result of the removal of aroma compounds which are bound wine proteins. This phenomenon was recently demonstrated for long chain fatty acids and their ethyl esters (1). Since these latter compounds are spectroscopically silent, their association with proteins is not easy to measure.

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.

Over the years, microoxygenation (MOX) has become a popular vinification technique to improve wine sensory qualities. However, among the impacting factors reported