Aroma, wine oxidation

Silva Ferreira, A. C., Hogg, T., and Guedes de Pinho, P. (2003). Identification of key odorants related to the typical aroma of oxidation-spoiled white wines. /. Agric. Food Chem. 51, 1377-1381. 

Ferreira, A.C.S., Barbe, J.C., and Bertrand, A. (2003). 3-hydroxy-4,5-dimethyl-2(5H)-luranone, A key odorant of the typical aroma of oxidative aged Port wine. 1. Agric. Food Chem., 51, 4356 363. 

The taste improvement due to ascorbic acid depends on several factors. The first is the type of wine. Ascorbic acid is of little interest in the case of wines made from certain varieties or very evolved wines—for example, barrel-aged wines oxidized white wines, botrytized sweet wine, and fine red wines. On the contrary, it improves the stability of fresh and fruity wines (generally young wines), having conserved their varietal aromas. 

The winemaker is always facing problems due to the weakness of grapes which composition is variable and different for each vintage. He tries to prevent oxidation and to work with soft conditions to preserve grapes components important for the wine s equilibrium. The sanitary state of the harvest is of first importance Grapes composition depends on the variety, terroir, viticulture and climatic conditions. The main objective for the winemaker is to keep and valorize grape components like aromas which will determine the quality of the wine... 

White musts and wines made without maceration contain very low amounts of flavonoids. However, when making white wine from white grapes, skin contact at low temperature is sometimes performed before pressing and fermentation to increase extraction of volatile compounds and aroma precursors. After 4h of skin contact, the concentration of flavanol monomers and dimers in must was increased threefold. Delays between harvest and pressing, especially if sulfur dioxide is added to prevent oxidation, as well as thorough pressing, similarly result in increased concentrations of flavonoids in white musts and wines. " " ... 

The impact of oxygen on wine aroma is likely to involve several oxidation mechanisms. One pathway involves pol) henol quinones, particularly in the case of the removal of unwanted sulfur-containing off-odors (RSH Mestres et ah, 2000), as illustrated in Fig. 4.4A. 

The impact of MOX upon reductive odors was included in the study of McCord (2003) for MOX at 5-10 mL/L/month over 5 months on a Cabernet Sauvignon wine in commercial scale tanks. Lower concentrations of methyl mercaptan and ethyl mercaptan were observed in the oxygenated wines, but no impact was seen upon disulfides, in spite of the suggestion that concentrations of the disulfides could increase due to direct oxidation of sulfides. Dimethyl sulfide concentrations were not affected, except that lower concentrations were seen in wines with added toasted oak staves or segments, with or without MOX. The concentrations of various oak extracted compounds were also measured in this study, with similar levels seen with and without MOX alongside appreciable increases due to the presence of the oak staves or segments in some cases (e.g., lactones and vanillin), oxygenation appeared to enhance aroma extraction. 

Cullere, L., Cacho, J., and Ferreira, V, (2007). An assessment of the role played by some oxidation-related aldehydes in wine aroma. /. Agric. Food Chem. 55, 876-881. 

The required dose of S02 should be estimated conservatively and measured precisely because excessive amounts of S02 destroy the aroma and taste of the wine and can delay the onset of fermentation. Also S02 in excess interferes with the natural development of bouquet in red table wines and diminishes the intensity of the red color. One should always use only the minimum amount of S02 required to inhibit bacterial growth and counter oxidation—more definitely is not better. 

The wine yeast, Saccharomyces fermentati, is able to form a film or veil on the surface of dry white wines of about 15-16% alcohol. This yeast produces agreeable smelling and tasting substances which dissolve in the wine and give it the aroma and flavor characteristic of Spanish fino sherries. To provide itself with energy for growth while in the film form on the surface of the wine, the yeast utilizes some of the oxygen from the atmosphere above the wine in the partially filled butt or barrel to oxidize some of the ethyl alcohol from the wine. The ethyl alcohol of the wine is not completely metabolized to carbon dioxide and water, however, but is oxidized to acetaldehyde—probably the principal compound in the complex mixture responsible for the aroma of this type of appetizer wine. 

Czs- and (-)-frans-rose oxide 6 are industrially produced perfume additives from citronellol. Several comparative studies have dealt with fruit and Gewiirtztraminer wine aroma (99JAFC665, 08JAFC1371). Guth... 

---