Teasing apart terroir: the influence of management style on native yeast communities within Oregon wineries and vineyards

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.

The overall quality of aged wines is in part due to the development of complex aromas over a long period (1.) The apparition of this aromatic complexity depends on multiple chemical reactions that include the liberation of odorous compounds from non-odorous precursors. One example of this phenomenon is found in dimethyl sulphide (DMS) which, with its characteristic odor truffle, is a known contributor to the bouquet of premium aged wine bouquet (1). DMS supposedly accumulates during the ten first years of ageing thanks to the hydrolysis of its precursor dimethylsulfoniopropionate (DMSp.) DMSp is a possible secondary by-product from the degradation of S-methylmethionine (SMM), an amino acid iden- tified in grapes (2), which can be metabolized by yeast during alcoholic fermentation.

In France, the definition of appellations of origins is entrusted to the Institut National des Appellations d’Origine. (‘NAO). With the increase in price of appellations of origin vine­yards and considering the interests at stake, Institut National des Appellations d’Origine and the Institut National de Recherche Agronomique (INRA) established a work group in 1993 in order to study the “terroir-wine” relationship as precisely as possible, taking into account the knowledge acquired by researchers of the INRA and the experience in the field of the agents of the INAO.

The chemistry of wine oxidation is captured in the reactions between the oxidation products, mostly reactive electrophiles, with other wine constituents. An understanding of both components and their reactions can lead to ideas and techniques to control and mitigate or enhance these reactions to allow for the desired development of the wine. Current investigations are yielding much useful information about oxidation reactions in wine.

The ongoing challenge of climate change is driving the need for novel oenological approaches aimed at finding effective environmental solutions.