Impact of drought stress on concentration and composition of wine proteins in Riesling

Del Barrio-Galán, R.a, b, Gómez-Parrini, A.a, Peña-Neira, A.b a Lallemand Inc. Chile y Compañía Limitada, Rosario Norte 407, piso 6, Las condes, Santiago, Chile b Department of Agro-Industry and Enology, Faculty of Agronomical Sciences, University of Chile, Post Office Box 1004, Santa Rosa 11315, La Pintana, Santiago, Chile It is well known that polysaccharides, mainly mannoproteins, play an important role on physical, chemical and sensory quality of wines. The ageing of white wines on lees is used in order to release higher amounts of polysaccharides by the autolytic processes in order to obtain higher-quality wines. However, this technique is too slow, because the temperature and pH conditions are not the most suitable for this process. In addition, it can also involve certain disadvantages such as a greater demand on winery resources, a longer period of wine storage, the appearance of reduction notes and some microbiological alterations.

The chemical mechanisms involved in oxidation/reduction potential of wine during winemaking and aging are affecting its color, aroma and taste. Chemical oxidation is one of the major causes of development of off-flavors during ageing1. Thus, the chemical changes in wine during storage should be controlled to ensure the sensory quality of the product and avoid consumer rejection that will compromise the economic value of the product. The 1-hydroxyethyl radical has been recognized as the key radical intermediate in the oxidative reactions in wine2. Based on the kinetic study of POBN-1-hydroxyethyl spin adduct formation in wines initiated via the Fenton reaction, a novel tool was recently developed in our laboratory to quantify the resistance of wines against oxidation3.

Varietal Riesling aroma relies strongly on the formation and liberation of bound aroma compounds. Floral monoterpenes, green C6-alcohols, fruity C13-norisoprenoids and spicy volatile phenols are predominantly bound to disaccharides, which are produced and stored in the grape berry during berry maturation. Grape processing aims to extract maximum amount of the precursors from the berry skin to increase the potential for a strong varietal aroma in the wine. Subsequent yeast selection plays an important part in this process.

Prefermentation steps of white winemaking are very important for controlling the stability and the sensory attributes of wines. Usually musts are clarified by cold settling to prevent the start of the fermentation, before racking big lees and thus limiting the appearance of vegetable or reduction off flavour while favouring an aromatic expression with low turbidity. Besides, to reach the protein stability, some white wines further require a bentonite fining, sometimes associated with negative effects on the sensory quality. This study aims to know the impact of musts heating after pressing on a Chardonnay wine in northern conditions by comparison with a classic cold racking of the must.

Commercial oenological tannins (TECs) are widely used in the wine industry. TECs are rich in condensed tannins, hydrolyzable tannins or a mixture of both. Wine grapes are a important source of proanthocyanidins or condensed tannins while oak wood possess a high concentration of hydrolyzable tannins (Obreque-Slier et al., 2009). TECs contribute with the antioxidant capacity of wine, catalyze oxide-reduction reactions and participate in the removal of sulfur compounds and metals.