Altered lignans accumulation in a somatic variant of Tempranillo with increased extractability of polyphenols during winemaking

Rapid and accurate quantification of grape berry phenolics, anthocyanins and tannins, and identification of grape varieties are both important for effective quality control of harvesting and initial processing for wine making. Current reference technologies including High Performance Liquid Chromatography (HPLC) can be rate limiting and too complex and expensive for effective field operations

ln the Mid-Loire Valley, in France, for the fast twenty years a network of experimental plots has been used to analyse the terroir effect on the behaviour of the Cabernet franc variety of grape. The study of the primary leaf area (SFI) for several vintages shows that it differs greatly from one terroir to another.

This study investigated if compositional differences between Shiraz and Cabernet Sauvignon grape varieties could influence the production of yeast-derived compounds. This work was based on the analysis of 40 experimental red wines made in triplicate fermentations from grapes harvested from two consecutive vintages in New South Wales (Australia). Grapes were picked at three maturity stages using berry sugar accumulation as physiological indicator, from nine commercial vineyards located in three different climatic regions (temperate, temperate-warm and warm-hot). A range of 30 yeast-derived wine volatiles including esters and alcohols were quantified by HS/SPME-GC/MS. Ammonia, amino-acids and lipids were analysed in the corresponding grapes. The juice total soluble solids (°Brix) in addition to the wine alcohol and residual sugar levels were also measured. The influence of grape maturity on wine ester composition was also variety dependent, particularly for higher alcohol acetate and ethyl ester of branched acids. This study highlights that varietal differences observed in Shiraz and Cabernet Sauvignon wines involve fermentation-derived compounds irrespective of the site (soil, climate, viticultural practices).

During wine alcoholic fermentation, yeasts produce volatile aroma compounds from sugar and nitrogen metabolism. Some of the metabolic pathways leading to these compounds have been known for more than a century.

Foliar application of urea may be an efficient way to alter grape and wine composition without increasing vine vigor. However, we know little about the impact of this practice on phenolic compounds and yeast assimilable nitrogen (YAN). Adequate YAN is required for an efficient and complete fermentation, while phenolics are particularly important for the sensory profile of red wines. The goal of this study is to test the impact of foliar urea application at veraison, compared to the traditional soil-applied nitrogen fertilization early in the season, on Syrah berry and wine composition in field conditions.