Ageing of sweet wines: oxygen evolution according to bung and barrel type

From the standpoint of wine aroma oxidation there are two effects observed: aroma degradation of oxygen sensitive compounds (polyfunctional mercaptans) and the appearance of new substances with high aromatic power (acetaldehyde, methional, phenylacetaldehyde, sotolon, alkenals, isobutanal and 2, 3-metylbutanals) (1-5). According to our experience, Strecker aldehydes are compounds with highest sensory relevance in the oxidative degradation of many wines (5-7).

3-Isobutyl-2-methoxypyrazine (IBMP) is one of the key molecules in wine aroma with a bell pepper aroma and a very low threshold in wine, 1-6 ng/L for white wine and 10-16 ng/L in red wine1. The differences in these thresholds are likely due to IBMP-non volatile matrix interactions. It has indeed been shown that polyphenols may influence the volatility of flavor compounds2. In the present study, we focus on IBMP-polyphenols interactions in relation to volatility and sensory perception in model wine solution. Methods: 1. GC-MS Static Headspace Analysis: Samples were analyzed by Static headspace analysis with an Agilent 7890A gas chromatograph coupled to HP 5975C mass spectrometry detector (Agilent Technologies, Santa Clara, CA, USA).

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).

Phenolic compounds are important quality indicators in red wine. A large number of polyphenols play an important role in wine development, contributing to the colour and the sensory perception of the wines. Anthocyanins are the pigments responsible for the colour in young red wines while tannins are the principal contributors to the bitterness and the astringency of the wines. Wine polyphenols are considered more complex molecules than grape phenolics, due to the enormous number of chemical reactions which take place during the entire winemaking process and storage, forming more stable compounds.

Nutrient availability – nitrogen, lipids, vitamins or oxygen – has a major impact on the kinetics of winemaking fermentations. Nitrogen is usually the growth-limiting nutrient and its availability determines the fermentation rate, and therefore the fermentation duration. In some cases, in particular in Champagne, grape musts have high nitrogen concentrations and are sometimes clarified with turbidity below 50 NTU. In these conditions, lipid deficiencies may occur and longer fermentations can be observed. To better understand this situation, a study was realized using a synthetic medium simulating the composition of a Champagne must : 180 g/L of sugar, 360 mg/L of assimilable nitrogen and a lipid content ranging from 1 to 8 mg/L of phytosterols (mainly β-sitosterol).