Influence of vineyard posts type on the chemical and sensorial composition of Sauvignon blanc and Merlot noir wines

[摘要] ENGLISH ABSTRACT: In recent years South African wines have been under the spotlight due to references in theinternational wine media to a distinctive 'burnt rubber' character. Many winemakers and wineexperts argued that the peculiar character could be ascribed to winemaking errors linked tomismanaged fermentation. An alternative possible source of the taint was identified in the coal tarcreosote used as a wood preservative in vineyard trellis systems. South African regulations allowfor the use of creosoted utility poles in agricultural land, but in Europe and USA their usage hasbeen highly regulated and even banned for certain applications. Contamination of foodstuff bypolycyclic aromatic hydrocarbons (PAHs) is one of the major motives for the banning of creosote inEurope and USA. Some of the compounds in the creosote mixture display very strong odourcharacteristics and for this reason it became the focus of attention for the present study.The overall aim of this study was to determine if vines trellised with creosoted posts couldaccumulate or absorb the various malodorous compounds deriving from the wood treatment ontothe grape berries. These compounds could then be extracted from the grape berries into the wineduring alcoholic fermentation, creating quality and sensory problems. Chapter 2 of this thesis givesan overview of the extensive literature that deals with methods of analysis of PAHs andmalodorous phenols using both Gas Chromatography (GC), as well as High Performance LiquidChromatography (HPLC). New methods for sample preparation, as well as analysis of PAHs usingHPLC-Diode Array Detector (DAD), were developed and the results reported in Chapter 3. It wasdemonstrated that Sauvignon blanc experimental wines contained only chrysene at very low levels.The concentrations of chrysene found in the experimental wines are within the prescribedparameters as established by The Commission of the European Communities. Since no other PAHcompounds were found in the samples analysed, it was concluded that the experimental wineswere safe for human consumption and complied with EU regulations. The effect of vineyard postson the sensorial characteristics of wine is discussed in Chapter 4. Creosoted poles were found tobe responsible for an off-flavour described as 'burnt rubber' and 'tarry' in Merlot wines producedfrom grapes grown in close proximity to the posts.Following some of the reported findings, new guidelines have been introduced in theIntegrated Production of Wine certification, which advise against the use of creosoted poles forvineyard trellising. This preliminary but important guideline will bring the South African wineindustry a step closer to the fulfilling the obligations for food safety as required by the legislation ofour major export partners. Future investigations are recommended to completely understand andevaluate the cumulative effect of creosoted posts in a fully trellised vineyard.

[发布机构] Stellenbosch University