Browsing by Author "Van Jaarsveld, F. P."
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- ItemThe effect of grape temperature at pressing on phenolic extraction and evolution in Méthode Cap Classique wines throughout winemaking(South African Society for Enology and Viticulture, 2018) Mafata, M.; Buica, A. S.; Du Toit, W. J.; Van Jaarsveld, F. P.Maintaining the chemical composition of a wine is essential for the wine industry. Although the sugar-acid balance of a wine is of primary sensory importance, individual acids and oenological parameters are equally important. The main focus of this study was to investigate the impact of grape temperature at harvest, on the oenological volatile acidity (VA), titratable acidity (TA), pH and alcohol levels and organic acid (citric, malic, pyruvic and succinic) characteristics of Méthode Cap Classique (MCC) wines during winemaking, produced from grape cultivars obtained from two regions. Chardonnay and Pinot noir grapes were obtained from Robertson (warmer) and Elgin (cooler) regions and were subjected to different temperature treatments, i.e. 0, 10, 25 and 30oC before further processing, including pressing, primary fermentation, blending, tirage, secondary fermentation, riddling and disgorging. Grape temperature was mostly responsible for a significantly higher pH of Robertson (0 and 10ºC) and lower pH (0ºC) of Elgin post-tirage wines. Chardonnay base wines from both regions that were vinified from grapes at lower temperatures (0 and 10oC) were richer in malic- and succinic acid, while Pinot noir wines from both regions were characterised by higher malic-, citric- and pyruvic acid. Pyruvic acid was only detected after the secondary fermentations in wines from both regions. To our knowledge, this study is the first to investigate the influence of grape temperature on the oenological and organic acid characteristics of MCC wines in different regions, and throughout different production stages.
- ItemThe effect of grape temperature on the sensory perception of Méthode Cap Classique wines(South African Society for Enology and Viticulture, 2017) Mafata, M.; Buica, A. S.; Du Toit, W.; Panzeri, V.; Van Jaarsveld, F. P.The production process of South African bottle-fermented sparkling wine, the Méthode Cap Classique (MCC), follows the traditional French method (méthode champenoise), although each cellar has its own unique additions to the method. South African winemakers use different techniques and blends to achieve their award-winning MCCs, but there have not been many scientific investigations of the science behind these wines. This project is one of the first scientific studies on MCC. MCC wines were made using Chardonnay and Pinot Noir grapes harvested over two vintages (2014 and 2015) from two regions (Robertson and Darling) and stored at 0°C, 10°C, 25°C and 30°C before processing. The study was aimed at investigating the effect of grape storage temperature on the sensory characteristics of MCCs. The aroma and taste of the final nine-month old MCCs were evaluated, with each region analysed separately. The study showed a grouping of the MCCs according to temperature treatments for both vintages. There were vintage differences in terms of the attributes cited and the frequency of citations. Based on the frequency of citation, the MCCs made 2014 from grapes stored at 0°C and 10°C were described by the judges as having a fruity, fresh and crisp aroma, whilst those made from grapes stored at 25°C and 30°C were described as having oxidised fruit, volatile acidity and solvent-like aromas. The judges perceived less oxidation and volatile acidity (VA) (in terms of the frequency of citation) in the aroma of the 2015 MCCs, although treatments at higher temperatures were still associated with less desirable attributes compared to treatments at lower temperature. This study shown that the temperature of the grape at the time of processing has a significant effect on the aroma of MCCs aged nine months, and not so much of an effect on the taste.
- ItemEffect of juice turbidity and yeast lees content on brandy base wine and unmatured pot-still brandy quality(South African Society for Enology and Viticulture, 2005) Van Jaarsveld, F. P.; Blom, M.; Hattingh, S.; Marais, J.The aims of this project were to identify a suitable grape juice clarification technique for the attainment of the optimal brandy base wine turbidity, to determine the importance of chemical components (volatile components and long-chain fatty acids) in brandy base wine and unmatured pot-still brandy quality, and to study the effect of yeast lees content on quality. Although common industry practice is to use the grape cultivars Colombar(d) and Chenin blanc for the production of brandy base wine, the optimal conditions for Chenin blanc have been defined in this study. The juice clarification treatments applied included no settling, cold settling, whisk, large- and small-scale centrifugation and bentonite. Yeast strain 228 was compared with VIN13, large-scale (L) distillation was compared with small-scale (s) distillation, and the use of no enzyme was compared with the use of pectolytic enzyme. The data for four vintages were compiled and evaluated. Settling with or without pectolytic enzyme, bentonite, small-scale centrifugation and whisk treatments gave clearer Chenin blanc juice, higher concentrations of certain volatile components and long-chain fatty acids, and higher quality brandy base wine and unmatured pot-still brandy. No settling and large-scale centrifugation yielded the most turbid and lowest quality products. There is a definite relationship between treatments, turbidity, concentrations of esters, higher alcohols and acids, and overall brandy base wine and unmatured pot-still brandy quality. The use of yeast strain VIN13 (as opposed to strain 228), in conjunction with an increased yeast lees content of 1.5x that is normally found in brandy base wine, yielded the best quality unmatured pot-still brandy. Based on the results of this study, it is possible to recommend the best juice clarification method(s) for optimal turbidity as well as optimal levels of yeast lees addition, and to identify chemical compounds that positively relate to quality.
- ItemPinking in white wines - a review(South African Society for Enology and Viticulture, 2020) Nel, A. P.; Du Toit, W. J.; Van Jaarsveld, F. P.In the late 1960s, a phenomenon was discovered in white wines. It was noted that certain white wines turned pink in the bottle. This phenomenon was dubbed as pinking. Research was done on the pinking to establish its cause and effect. Analysis of SO2, pH and polyvinyl polypyrrolidone (PVPP) showed that a minimum of 45 mg/L of SO2 were needed for the wine not to be susceptible to pinking. Tests on the decrease in pH showed that there was no increase in pink colour with a decrease in pH, which meant that monomeric anthocyanins were not the cause of pinking. Recent research claims that malvidin-3-Oglucoside is the most abundant monomeric anthocyanin found in pinked wines and could be the cause of pinking. This led to the theory that phenols contribute to pinking susceptibility, and this was accepted as fact in recent years. The establishment of a pinking assay in 1977 made the testing for pinking easier and cheaper for winemakers. The sales of PVPP increased as winemakers worked preventatively with their wine to decrease susceptibility to pinking. This review attempts to describe the history of pinking, the establishment of the assay, as well as to describe factors that could lead to pinking susceptibility in white wines.
- ItemRapid induction of ageing character in brandy products : ageing and general overview(South African Society for Enology and Viticulture, 2012) Van Jaarsveld, F. P.; Hattingh, S. M.Ageing is one of the most important and most costly factors determining the quality of distilled beverages. As part of a broader study that investigated techniques for the rapid induction of a desirable ageing character in brandy products, the effect of maturation for eight months at room temperature and below 0°C in glass bottles, and the relationship/correlation between treatment, chemical composition or wood-derived congener concentrations and pot-still brandy sensory quality, are reported on. Extracts representing different oak types (American or French), levels of toasting, suppliers (i.e. cooper or commercial), types of medium (ethanol or water), concentration types (open or reduced pressure) and concentration levels (by 45, 65 or 85%) were added to pot-still spirit and stored for eight months in glass containers. Matured and unmatured (control) pot-still brandy samples were analysed for wood-derived compounds by means of HPLC and GC. The different treatments brought about chemical changes with a noticeable impact on the acceptability of oak extracts and the overall quality of pot-still brandies. Through application and selection of the correct oak type and treatment combinations, it therefore was possible to rapidly produce good quality brandies without the use of expensive oak barrels. Maturation in glass bottles had a lesser impact on further improvement of the final product, not the same as the reported improvement from ageing in wooden barrels. The production of good quality brandies and the rapid induction of the ageing character through certain treatment combinations, with little need for further maturation, therefore was achieved in glass. The complexity of brandies aged in glass rather than wooden barrels might be different, since ageing in wooden barrels brings about all the characteristics, complexities and flavours that characteristically evolve over time under the more oxidative conditions in wooden barrels. Future research should focus on a combination of both technologies, using certain oak treatment combinations together with traditional barrel maturation for the improvement and rapid induction of the ageing character in brandy products.
- ItemRapid induction of ageing character in brandy products. Part I. Effects of extraction media and preparation conditions(SASEV, 2009-10) Van Jaarsveld, F. P.; Hattingh, S.; Minnaar, P.; Blom, M.The purpose of this study was to investigate the use of different wood types and treatments, and extraction media to induce rapid ageing of brandy. Extracts were prepared from American and French oak, specially prepared and supplied by a cooper, and from commercially obtained oak; both representative of different toasting levels, including untoasted, light, medium and heavy toasted. To extract the wood components, wood chips in either 55% (v/v) neutral wine spirits or water media were boiled under reflux. Distillation was followed by either open (higher boiling temperature) or closed (vacuum or reduced pressure - lower boiling temperature) concentration of the decanted solvent by 45, 65 and 85% (v/v). The concentrated extracts were fortified. Screened extracts were added to unmatured pot-still brandy and aged for eight months at room temperature in glass containers. Controls were stored below 0°C. Matured and unmatured (control) pot-still brandy samples were analyzed for wood-derived congeners by means of HPLC and GC. This article focuses on the effects of the extraction media, and on level and method of concentration (open and reduced pressure) on sensory quality and chemical composition. The treatments that gave acceptable extracts, and the best overall quality pot-still brandy were those that entailed (1) using ethanol instead of water as extraction medium, and (2) levels of concentration above 45% (v/v). Open and reduced-pressure concentrations showed little difference in the quality of the products yielded. Treatments yielding the most acceptable extracts and best overall quality pot-still brandy generally also contained higher concentrations of volatile and less volatile wood-derived congeners. Multivariate data analysis was conducted on the pot-still brandy samples representing the different treatments. Discriminate analysis provided better separation of samples than principal component analysis.
- ItemRapid induction of ageing character in brandy products. Part II, Influence of type of oak(SASEV, 2009) Van Jaarsveld, F. P.; Hattingh, S.; Minnaar, P.As part of a broader study that investigated techniques for the rapid induction of the needed ageing character in brandy products, the effect of oak type on quality and chemical composition of oak wood extracts and matured and unmatured potstill brandy, is reported on. Extracts, prepared from American and French oak chips supplied by a South African cooper, and from commercially obtained oak, and representing different levels of toasting, were added to 70% (v/v) unmatured pot-still brandy and stored for eight months in glass containers (Schott bottles) at room temperature, or in the case of controls, below 0°C. Matured and unmatured (control) pot-still brandy samples were analysed for wood-derived congeners by means of HPLC and GC. Although French oak initially yielded better quality products, these effects lost prominence and, after eight months maturation, yielded similar sensory quality to American oak. French oak samples had higher concentrations of wood-derived congeners (including eugenol, the furan derivatives and aromatic aldehydes). However, the American oak generally contained higher concentrations of oak lactones than their French counterparts, with higher proportions of the more sensorially potent cis-form of lactone than its trans-isomer.
- ItemRapid induction of ageing character in brandy products. Part III, Influence of toasting(SASEV, 2009) Van Jaarsveld, F. P.; Hattingh, S.; Minnaar, P.As part of a broader study that investigated techniques for the rapid induction of the needed ageing character in brandy products, the effect of oak wood toasting on quality and chemical composition of oak wood extracts and matured and unmatured pot-still brandy, is reported on. Extracts, prepared from oak chips supplied by a South African cooper, and from commercially obtained oak, and representing different oak types and levels of toasting (i.e. untoasted, light, medium and heavy), were added to 70% (v/v) unmatured pot-still brandy and stored for eight months in glass containers (Schott bottles) at room temperature, or in the case of controls, below 0°C. Matured and unmatured (control) pot-still brandy samples were analysed for wood-derived congeners by means of HPLC and GC. Toasted, as opposed to untoasted oak, gave acceptable extracts, the best overall quality pot-still brandies and generally higher concentrations of volatile (GC-determined) and less volatile (HPLC-determined) wood-derived congeners. Toasting provoked an important separation as indicated by discriminant analysis.