Role of 3-methyl-2,4-nonanedione in the flavor of aged red wines.

GC-MS in chemical ionization mode (CI) was used as a simple, sensitive method for assaying 3-methyl-2,4-nonanedione (MND) in 67 red wines. MND content was shown to be lower in nonoxidized red wines and higher in oxidized red wines, that is, systematically exceeding the perception threshold (62 ng/L). Concentrations up to 340 ng/L in the most oxidized red wines were also evidenced. According to these quantitative data, the presence of MND alone was shown to modify significantly the flavor of the red wine as evaluated from fresh fruit flavor in red wine without MND to aromatic expression of rancio in wines with elevated concentrations (308.9 ng/L). Incidence of oxygen on its formation was also investigated. For the first time, elevated concentrations of this compound in various wines were demonstrated, that is, white, rosé, botrytized wines, and fortified wines made with over-ripened grapes. The lowest levels (2.9 ng/L) were found in nonoxidized white wines, whereas the highest levels were found in oxidized botrytized wines (293.8 ng/L). These results tend to demonstrate that MND is in general a good marker of oxidation in wines made with a maceration step between the skin and the pulp. These preliminary results provide a new analytical explanation of what is known in enology as the "vin de garde" concept.