Influence of toasting oak wood on ellagitannin structures

This study investigates the effect of wood chips addition during the alcoholic fermentation on the phenolic
composition of the produced wines. A series of wood chips, originating from American, French, Slavonia
oak and Acacia were added at the beginning of wine alcoholic fermentation. Besides, a mixture consisting
of 50% French and 50% Americal oak chips were added during the experimentation. The wine samples
were analyzed one month after the end of malolactic fermentation, examining various chemical
parameters such as total anthocyanins, total phenolic content, tannins combined with protein (BSA) and
ellagitannin content.

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.

Malolactic fermentation (MLF) is a secondary step in the vinification process and it follows alcoholic fermentation (AF) which is predominantly carried out by Saccharomyces cerevisiae. These two processes result in the degradation of metabolites to produce secondary metabolites which also contribute to the final wine flavour and quality. AF results in the production of ethanol and carbon dioxide from sugars and MLF stems from the degradation of L-malic acid (a dicarboxylic acid) to L-lactic acid (a monocarboxylic acid). The latter process results in a smoother texture as the acidity of the wine is reduced by the process, it also adds to the flavour complexity of the wine.

Wine aroma is influenced by several viticultural and oenological factors. In this study we used experimental wine making in a full factorial design to determine the impact of grapevine age, must turbidity, and yeast strain on the aroma of Vitis vinifera L. cv. Riesling wines. A recently developed, non-targeted SPME-GC-MS fingerprinting approach for wine volatiles was used. This approach includes the segmentation and mathematical transformation of chromatograms in combination with Parallel Factor Analysis (PARAFAC) and subsequent deconvolution of important chromatogram segments.

The grapevine is an important economical crop that is very sensitive to climate changes and microclimate. The observations made during the last decades at a vineyard scale all concur to show the impact of climate change on vine physiology, resulting in accelerated phenology and earlier harvest (Jones and Davis 2000). It is well-known that berry content is affected by the ambient temperature. While the first experiences were primarily conducted on the impact of temperature on anthocyanin accumulation in the grape, few studies have focused on others component of phenolic metabolism, such as tannins.