Botrytized wines oxidation

Numerous y- and 8-lactones were identified in Tokaji aszu grapes (Miklosy and Kerenyi, 2004 Miklosy et al., 2004). The odor notes of the y-lactones were described as resin- and caramel-like, roasted, or honey, while the 8-lactones exhibited characteristic notes of coconut, chocolate, and peach. The same lactones had been identified earlier from botrytized wines but not from normal wines (Schreier et al., 1976). Lactones are mostly found in oxidatively aged wines but seem to develop in fruit due to the oxidizing effect of B. cinerea, water loss, or Maillard reactions (Miklosy et al., 2004). 

Cessation of fermentation is one of the technical problems in botrytized wine production that needs further research and development. Dimethyldicarbonate (DMDC) is now considered a reliable inhibitor which could replace some of the S02. Although DMDC has proven suited for treating wines especially just before bottling, its use in Sautemes production has been investigated (Divol et al., 2005). The results showed that DMDC at a rate of 100-200 mg/1 stopped fermentation but did not replace the antioxidant functions of SO2. Sulfite addition was necessary to limit wine oxidation and yeast reactivation. 

The infection with Botrytis cynerea is responsible for certain changes in the carbohydrate composition of musts and wines, mainly by oxidation. Botrytized wines contain xylosone and 5-oxo-fructose (Ribereau-Gayon 1973), a hexodiulose which is formed by oxidation of fructose it has been found in botrytized musts varying within 80-150 mg/L (Barbe et al. 2000, 2002). Acid sugars also increase (see below). 

On the basis of these findings, DMDC was initially authorized in the United States, then in other countries. Like ethyl pyrocarbonate, DMDC is most effective at the time of bottling, although it has also been suggested for use in stopping the fermentation of sweet (botrytized) wines (Bertrand and Guillou, 1999), thus reducing the amount of SO2 required. In any case, a certain quantity of free SO2 is always necessary to protect the wine from oxidation. 

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. 

Pour Nikfardjam, M., Laszlo, G., and Dietrich, H. (2006). Resveratrol-derivatives and anti-oxidative capacity in wines made from botrytized grapes. Food Chem. 96, 74-79. 

Fedrizzi, B., Zapparoli, G., Finato, F., Tosi, E., Turri, A., Azzolini, M., and Versini, G. (2011). Model aging and oxidation effects on varietal, fermentative, and sulfur compounds in a dry botrytized red wine. J. Agric. Food Chem. 59,1804—1813. 

The most abundant SO2 combination due to Gluconobacter results in 5-oxofhictose, which is not metabolized by yeast, so it remains unchanged in Ihe wine. It is formed by oxidation of any fructose in the medium, as is the case in grape must. In a botrytized must where the fungus has developed to its most advanced stage, Ihis compound alone... 

The oxidation affecting sulfurous acid forms sulfuric acid. At the pH of wine, it is almost entirely in the form of sulfate. In botrytized and non-botrytized sweet wines with elevated free SO2 concentrations, a considerable amount of sulfate can be formed (0.5 g/1). Less is formed in dry white and red wines, especially those stored in tanks. In the case of barrel-aged wines, the formation of sulfate by the oxidation of free SO2 accumulates with the amount resulting from the combustion of sulfur in the empty barrels. This formation lowers the pH and harshens the wine. This phenomenon contributes to the decrease in quality of wines stored in barrels for an excessively long time. 

Sulfiting juice intended for botrytized sweet wine production has often been criticized. This operation leads to increased concentrations of bound sulfur dioxide, which remains definitively in the wine. Subsequent SO2 additions must therefore be limited to remain within legal total SO2 limits, thus compromising the microbiological stabilization of wine. In practice, this inconvenience of sulfiting is attenuated by the fact that only 40-60% of the SO2 added in juice is found in the bound form in wine. The rest is oxidized into SO3. 

As with dry white winemaking, overclarification can lead to large fermentation problems and increased acetic acid production. Must turbidity should not be as low as in dry white winemaking (100-200 NTU) 500-600 NTU or even a slightly higher turbidity is perfectly acceptable. Moreover, botrytized sweet wines are not subject to the same problems related to insufficient clarification as dry white wines—the development of reduction odors and vegetal tastes, oxidability, etc. 

The organoleptical quality of botrytized sweet wines improves considerably after several months of barrels maturation and several years of bottle aging. The bouquet takes on finesse and complexity—reminiscent of confect fruit and toasted almonds. The wine becomes harmonious on the palate. The sweetness is perfectly balanced by the alcohol and a note of acidity gives a refreshing finish. The wines are not heavy and syrupy, in spite of their high sugar concentration. These transformations remain poorly understood even today. They occur in conditions, particularly oxidation-reduction conditions, reminiscent of red wine maturation and aging. 

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