Effect of oxygen managment on white wine composition
Thesis (MScAgric)--Stellenbosch University, 2020.
ENGLISH ABSTRACT: Premature oxidation in white wine is a constant problem for winemakers. A number of studies have shown that dissolved oxygen and elevated temperatures have a negative effect on wine composition, but these were often done using extreme conditions such as very high temperatures and excessive oxygen additions. During wine oxidation, compounds associated with positive aromas decrease and those linked to aged and oxidized wines increase in concentration. There are numerous ways to combat oxidation using antioxidants and reductive winemaking techniques. However, a recent study has found wines in South Africa to be bottled at a total packaged oxygen level of between 1.5 and 7.5 mg/L. As these levels could reduce antioxidant capacity, understanding how these levels affect wine ageing is paramount. Furthermore, according to our knowledge, a study of dissolved oxygen concentrations representative of the industry at bottling in conjunction with different storage temperatures has not been done before. In this study, a Sauvignon blanc and Chenin blanc wine were exposed to no oxygen additions and additions of 3 and 6 mg/L and then aged at 15°C and 25°C for 12 months. These wines were analysed chemically and sensorially after six and twelve months ageing. Temperature and dissolved oxygen concentrations were found to significantly affect antioxidants such as glutathione and sulphur dioxide concentrations. Wine volatiles, such as 3-mercaptohexyl acetate, isoamyl acetate, diethyl succinate, hexanoic acid, octanoic acid and decanoic acid were often influenced by higher storage temperatures. Over time, storage temperature was found to significantly affect the sensory descriptors of the Sauvignon blanc wine more than the Chenin blanc wine. Furthermore, as winemakers seek to avoid oxidation in wine, removing dissolved oxygen from wine by sparging with inert gasses is a common industry practice. However, little research has been done to investigate the relevant parameters of sparging efficiency and the direct effects of sparging on wine chemical composition. This study sought to build upon limited previous research and, for the first time, investigate the effects of sparging on wine chemical composition. Various parameters of sparging such as temperature, flowrate, gas composition and application of a diffusion stone were investigated and found to affect sparging efficacy. Sparging with both nitrogen and a mixed gas of nitrogen and carbon dioxide significantly affected the concentrations of dissolved carbon dioxide in wine, where the amount of dissolved carbon dioxide lost was dependent on factors such as wine temperature, gas flowrate and gas composition. Sparging wine with inert gasses did not affect the measured white wine aromatic or antioxidant chemical composition.
AFRIKAANSE OPSOMMING: Geen opsomming