Grape and wine quality of V. vinifera L. cv. Cabernet Sauvignon/99R in response to irrigation using winery wastewater

[摘要] ENGLISH ABSTRACT:Grapevine performance and wine quality are influenced by various factors, two of the most important being the availability and quality of irrigation water. In relatively dry countries such as South Africa the conservation and effective use of water is of utmost importance. Expected increases in temperature and decreases in rainfall in the future due to climate change impacts highlights the importance of water conservation. This inspired investigations into possible alternative irrigation water sources and therefore the possibility of vineyard irrigation using winery wastewater is of utmost importance for the sustainability of the wine industry.Winery wastewater contains higher concentrations of certain elements other than water generally used for vineyard irrigation, the most important differences being Na and K levels. Furthermore, winery wastewater contains larger populations of microorganisms such as yeasts, lactic acid bacteria and acetic acid bacteria, typical associated with wine production. If irrigation using winery wastewater affects the uptake of certain elements or alters grapevine water status, it may affect grapevine growth, juice and wine composition. Furthermore, if juice and wine composition is affected wine composition and sensorial quality may be affected.Cabernet Sauvignon/99R grapevines, growing in a sandy soil in the Breede River Valley, were subjected to eight irrigation treatments using augmented winery wastewater in addition to irrigation using raw river water as control. The study was carried out during the 2010/11 and 2011/12 seasons. The various wastewater irrigation treatments were made up by augmenting winery wastewater with raw river water to obtain a target chemical oxygen demand (COD) concentration. In this study, the level of COD in the irrigation water is a direct indication of water quality, the two being indirectly proportional. The eight wastewater irrigation treatments ranged from 100 mg/L COD up to 3000 mg/L COD.The first objective of the study was to determine the effect of irrigation using augmented winery wastewater on grapevine response, with regards to vegetative growth, berry development and berry composition. The various wastewater irrigation treatments did not affect grapevine vegetative growth or reproductive growth, including yield, throughout berry development up to harvest. Berry sugar accumulation and evolution in acid concentrations were also not affected. An increase in berry juice pH was observed with an increase in the level of COD in the augmented winery wastewater only in the second season. The amount of elements, ions and heavy metals in juice was not affected by wastewater irrigation, indicating that there was no absorption by the grapevines. Berry skin thickness, colour and phenolic content as well as yield and its associated components were not affected by irrigation using augmented winery wastewater.The second objective of the study was to determine the effect of irrigation using augmented winery wastewater on wine microbial and chemical composition, fermentation performance and wine sensorial characteristics. The natural yeast and bacteria flora of juice was not affected by the various wastewater irrigation treatments. In addition, the ability of the inoculated yeast and lactic acid bacteria strains to conduct their respective fermentation processes were not affected. With the exception of total titratable acidity (TTA) and pH, irrigation using augmented winery wastewater did not affect wine chemical composition with regards to basic wine parameters as well as colour, phenolic and tannin composition. Similar to juice, phosphorus and selected ions were not affected. None of the measured wine sensorial characteristics were affected by irrigation using augmented winery wastewater.The third objective of the study was to investigate the effect of direct contact between berries and winery wastewater on wine sensorial characteristics. The study focussed on the transference of off-flavours from the wastewater into the wine and the occurrence of off-flavours as a response to contact with winery wastewater. Wine colour and general sensory wine descriptives were not affected by direct contact with winery wastewater. The presence of a winery wastewater-like off-odour and volatile acidity was, however, more detectable in wines made from berries that were in contact with the most concentrated wastewater. Therefore, it may be possible for off-odours to be transferred from the winery wastewater into the wines, or that off-odours are formed as a direct or indirect result of contact with winery wastewater.Under the given conditions, results obtained in this two seasons of the study suggest that irrigation using augmented winery wastewater does not affect grapevine performance or wine quality substantially. The major impact that was observed was an increase in wine pH and a decreasing trend in TTA. Both these parameters could be rectified by simply adding acid to the wines. Therefore, irrigation using augmented winery wastewater may be considered as a possible future alternative source for vineyard irrigation. It is, however, important to remember that some of the effects of wastewater irrigation may be cumulative and could possibly arise only after several years. Furthermore, different field conditions and cultivars may respond differently.

[发布机构] Stellenbosch University