Production of Botrytized Wines

Due to the particular raw material, making botrytized wines is major challenge for winemakers. In addition to the uncertain nature of noble rot development, low grape and juice yield, technological difficulties, and the high risk of spoilage, make producing these wines one of the world s most expensive. 

Various grape-picking strategies and techniques are applied in botrytized wine making. Regardless, a prolonged or late harvest is necessary a factor which implies risk of losing the crop to bunch rot, other infections or frost under adverse weather conditions. 

The less labor intensive, but still expensive, harvest method involves waiting for as long as possible, and then picking the botrytized and healthy grapes together as whole bunches. This method is used all over the world in the making new-style botrytized wines. 

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The production of botrytized wines is initially limited by the special conditions required for noble rot development. Noble rot develops concurrent with berry dehydration. In the process, compounds present in the overripe grapes and produced by B. drierea become extremely concentrated. The result is the generation of wines with very high sugar and extract contents, and exceptional aroma richness. 

Botrytized wines have been made for a very long time in Europe, and also are produced in increasing amounts in Australia, New Zealand and South Africa. Although only a few types of botrytized wines are regularly produced, their occasional production is possible in many regions, depending on the weather conditions. 

The unique chemical composition of botrytized must greatly impacts the products and by-products of alcoholic fermentation, as well as subsequent reactions. The changes have been extensively studied by German and French authors and have been reviewed by Dittrich (1977, 1989), Jackson (2008), Ribereau-Gayon et al. (2000), and Dittrich and Grossmann (2011). The chemical composition of some traditional (German and Hungarian) botrytized wine styles are illustrated in Table 6.5. 

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. 

Malolactic fermentation is often viewed as the main source of polyamines in wine production (Marcobal et al., 2006). Thus, their presence is more significant in red wines than in white ones. Of white wines, sparkling wines, biologically aged wines, and botrytized wines might be the most susceptible to biogenic amine formation. 

Nelson, K. E. and Nightingale, M. S. (1959). Studies in the commercial production of natural sweet wines from botrytized grapes. Am. J. Enol. Vitic. 10,135-141. 

The biology of Botrytis cinerea and its development in the form of noble or vulgar rot have been described in (Section 10.6). This overripening process, noble rot, permits the production of great botrytized sweet wines. These exceptional wines can only be made in specific conditions. Their production is therefore limited. 

The artificial induction of noble rot would greatly facilitate making botrytized sweet wine, extending their production to countries where conditions are unfavorable for the natural development of noble rot. Experiments have long been performed to this end. In the earliest work, Nelson and Amerine (1956) unsuccessfully tried to induce its development in the vineyard by inoculation. The necessary moisture condition after inoculation was impossible to reproduce under field conditions. In addition, the method creates the risk that other fungi (Penicillium, Aspergillus, Rhizopus), yeasts and, acetic acid bacteria could develop if unfavorable weather conditions arose (Dittrich, 1977). 

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. 

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