Ethyl esters interact with the major wine Thaumatin Like Protein VVTL1

The above-ground parts of plants, which constitute the phyllosphere, have long been considered devoid of bacteria and fungi, at least in their internal tissues and microbial presence there was long considered a sign of disease. However, recent studies have shown that plants harbour complex bacterial communities, the so-called “microbiome”[1]. We are only beginning to unravel the origin of these bacterial plant inhabitants, their community structure and their roles, which in analogy to the gut microbiome, are likely to be of essential nature. Among their multifaceted metabolic possibilities, bacteria have been recently demonstrated to emit a wide range of volatile organic compounds (VOCs), which can greatly impact the growth and development of both the plant and its disease-causing agents.

Fermentative aromas (especially esters and higher alcohols) highly impact the organoleptic profile of young and white wines. The production of these volatile compounds depends mainly on temperature and Yeast Available Nitrogen (YAN) content in the must. Available dynamic models predict the main reaction
(bioconversion of sugar into ethanol and CO2 production) but none of them considers the production kinetics of fermentative aroma compounds during the process of fermentation. We determined the production kinetics of the main esters and higher alcohols for different values of initial YAN content and temperature, using an innovative online monitoring Gas Chromatography device.

Recent studies have demonstrated the role of certain lactones, particularly 2-nonen-4-olide, and volatile thiols (3-sulfanylhexan-1-ol) in the over ripped aromas of noble rot sweet wines (Stamatopoulos et al. 2014ab). These compounds are partly formed during the maturation and under the activity of B. cinerea on grapes. This research was carried out in the vineyard of Sauternes with aim to better understand their genesis depending on the grape over-ripening on two different soil types during 3 vintages. Thus, the study was conducted, with the Sémillon grape, during vintages 2012, 2014 & 2015, at 4 stages of over-maturation of the grapes (healthy, pourri plein, pourri roti, pourri roti + 15 days) considering two vineyard plots with different soil characteristics (calcosol & peyrosol) planted with the 315 Sémillon clone and grafted on 101-14 rootstock respectively in 1981 and 1980 and cultivated with the same vineyard management. Volatile lactones were assayed by liquid-liquid extraction followed by GC/MS analysis and the precursors of 3-sulfanylhexanol by an adaptation of the method by Capone et al. 2010 (SPE-
UPLC/FTMS).

Climate change and harvest date decisions have led to the evolution of must quality over the last decades. Increases in must sugar concentrations are among the most obvious consequences, quantitatively. Saccharomyces cerevisiae is a robust and acid tolerant organism. These properties, its sugar to ethanol conversion rate and ethanol tolerance make it the ideal production organism for wine fermentations. Unfortunately, high sugar concentrations may affect S. cerevisiae and lead to growth inhibition or yeast lysis, and cause sluggish or stuck fermentations. Even sublethal conditions cause a hyperosmotic stress response in S. cerevisiae which leads to increased formation of fermentation by-products, including acetic acid, which may exceed legal limits in some wines.

The impact of minute amounts of headspace oxygen on the post-bottling development of wine is generally considered to be very important, since oxygen, packaging and storage conditions can either damage or improve wine quality. This is reflected in the generalised use of inert bottling lines, where the headspace between the white wine and the stopper is filled with an inert gas. This experiment aimed to address some open questions about the chemistry of the interaction between wine and oxygen, crucial for decisions regarding optimal closure. While it is known that similar amounts of oxygen affect different wines to a variable extent, our knowledge of chemistry is not sufficient to construct a predictive method.