Volatile compounds and wine aging

Abstract

Oak wood barrel aging of wine fromthe end of fermentation to bottling is a common practice at wineries, chiefly for red wines but sometimes also for white wines. Bottle aging usually takes place after the barrel aging period, especially in the case of red wines. Although some white wines like Riesling, Chenin Blanc or Colombar wines are consumed one or two years after bottling, achieving during this time a characteristic "bouquet of aging". The same is not true for wines from other varieties in which oxidation of the terpenes and hydrolysis of acetates and ethyl esters of fatty acids contribute to the loss of the flowery and fruity character of young white wines (Rapp and Marais 1993; González-Vinas et al. 1996). Generally speaking, aged wines are associated with wines that have spent a period of time in an oak barrel acquiring a special aroma that is well appreciated by the consumer, reaching a high price in the marketplace. For these reasons, this chapter is focussed on all those aspects that may affect the volatile composition of oak wood, and consequently of oak aged wine. Oak barrels are regarded as being conducive to the sensory development of wines, though the events taking place in the barrel are extremely complex. A series of stabilizing reactions that affect wine colour and clarity, structural changes in the phenolics and new aroma formation all take place during oak wood aging. None of these reactions occurs in tanks or bottles, which are inert, do not interact with the wine, and do not allow the controlled oxidation that takes place in oak barrels. The release of oak wood aromas is one of the primary reasons why wines are made to undergo aging in the wood. This makes it necessary to take into account the different factors regulating the release of volatile components from the oak to the wine. These factors include the type of oak employed and the geographical origin of the oak (Mosedale and Ford 1996; Chatonnet and Dubourdieu 1998; Pérez-Coello et al. 1999; Fernández de Simón et al. 2003), the drying treatment to which the oak has been subjected (Sefton et al. 1993; Masson et al. 2000b; Doussot et al. 2002), the degree of toasting (Chatonnet 1999; Hale et al. 1999; Cadahá et al. 2003), and the length of time a wine spends in the barrel, along with barrel age and usage, i.e., the number of times a barrel has been used (Singleton 1995; Escalona et al. 2002; Pérez-Prieto et al. 2002). Several chemical reactions that happen in the barrel during aging can also affect the final volatile composition of wines. Among these reactions is found the oxidation due to the entry of oxygen across the pores of the wood, which modify both the wine volatile compounds and those extracted from wood. On the other hand, microorganisms, proceeding from the wine or from the barrel, especially lactic bacteria and yeasts, can produce important volatile compounds from a sensorial point of view, like vinylphenol and vinylguaiacol (Jarauta et al. 2005). Finally, the adsorption of certain wine volatiles by the lees and the barrel itself (Chatonnet et al. 1992a; Ramŕez Ramŕez et al. 2001; Jiménez Moreno and Anćn Azpilicueta 2007), together with the possible changes that can occur during the additional bottle aging period (Pérez-Prieto et al. 2003), will also cause modifications in the final aromatic composition of the wine. The long aging process normally increases the price of the final product, since the wine has to be left in the barrels before it can be brought to market. For this reason, the use of oak chips or staves as an alternative for the aging process has been widely considered in the last few years (Ducournau et al. 1999; Gutiérrez Afonso 2002; Frangipane et al. 2007). However, since oak barrel aging involves something more than the simple transfer of compounds from the wood to the wine, this new type of skill will have to be optimised to obtain a quality product. © Springer Science+Business Media, LLC 2009.