Cadmium Content of South African Table Wines

Red and white South African table wines from the major wine producing districts were analysed for cadmium content. Only three wines had a slightly higher concentration than 0,010 mg/ t The average cadmium concentration was 0,003 mg/ f, and no relationship between cadmium content and origin could be determined

The Effect of Juice Clarity and Several Conditions Promoting Yeast Growth on Fermentation Rate, the Production of Aroma Components and Wine Quality

In cellar practice grape juice is preferably made as clear as possible, and fermentations take place under strictly anaerobic conditions. In the laboratory, however, the fermentation rate of EK-filtered and de-aerated juices was always so much slower than that of juices obtained by normal cellar routine that no dry wines could be prepared unless fermentation stimulating methods were applied. Apparently in most cellar fermentations sufficient amounts of oxygen and/or of yeast growth promoting steroids from the grapes are present to complete fermentation, but the exact amounts present are unknown. In practice problems with lagging fermentation could occur in cases where clarifying and de-aeration of juice were performed too rigorously. Grape juice was clarified by diverse methods, and white wines were prepared from the juices under various conditions in order to study the effect of de·aeration, addition of settled juice with residual turbidity, micro-aeration and application of ergosterol suspensions on fermentation rate. EK-filtered juices were used to experiment with methods for reactivating lagging fermentation and also forinvestigating the effect of fermentation conditions on the production of wine volatiles. With the aid of the above-mentioned fermentation stimulating means the fermentation of EK-filtered juices could be completed within an acceptable period of time. Steps to reactivate lagging fermentations should be taken as early as possible, although additions of settled juice were often successful, even when applied at a late stage during fermentation. Filtered juice from different cultivars and origins behaved in a markedly similar way with regard to fermentation and the production of volatile components. Filtration of juice caused partial loss of the cultivar character of the wine but wines from filtered juice with additions of ergosterol were nevertheless allotted the highest scores during organoleptic evaluation. The production of higher alcohols depends on the degree of juice turbidity and fermentation temperature. In clear filtered juice, however, the production of higher alcohols was independent of fermentation temperature. The formation of acetates of higher alcohols is greatly enhanced, by adding ergosterol to the filtered juice

Grape Maturity and Wine Quality

Several indices calculated from grape juice analyses were submitted to statistical analyses in order to determine correlations of these indices with quality of wine made from grapes at different stages of maturity. Curvilinear relationships were obtained enabling an optimum point to be calculated relating grape maturity to maximum wine quality. The application of skin contact in the case of white wine cultivars resulted in earlier maxima for wine quality, thus compensating to an extent for earlier harvesting. The cultivars Chenin blanc, Colombar, Pinotage and Cabernet Sauvignon were examined as outlined above over several years

Initial Study on the Guava Aroma of Chenin Blanc and Colombar Wines

An initial study indicated the importance of mercaptan on the aroma of Colombar and Chenin blanc wines. A synthesized mercaptan viz. 4-methyl-4-mercapto-pentan-2-one when added to neutral wine effected a Colombar or Chenin blanc wine aroma. The importance of sulphur components on wine aroma is emphasized

The quantitative determination and some values of dimethyl sulphide in white table wines

A gaschromatographic headspace method has been developed for the quantitative determination of dimethyl sulphide (DMS) in wines. The standard deviation of the method was in the order of 6%.Application of the method to the analysis of several white wines showed DMS values which varied from O to over 400 µg/1. From analytical data it appeared that DMS developed in the bottle and could as such possibly contribute to bottle bouquet. It was found that maturecl Riesling wines had particularly high concentrations of DMS.Die quantitative Bestimmung von Dimethylsulfid in weißen Tafelweinen sowieeinige Angaben über seine KonzentrationFür die quantitative Bestimmung von Dimethylsulfid (DMS) in Wein wurde unter Verwendung der „headspace"-Technik und von Dichlormethan als Standard eine gaschromatographische Methode entwickelt. Die Genauigkeit der Methode liegt bei einer Standardabweichung von 6%. Bei der Anwendung der Methode auf eine Reihe von Weißweinen wurden DMS-Werte zwischen O und über 400 µg/l ermittelt. DMS scheint sich während der Ausreifung des Weines in der Flasche zu entwickeln und könnte zum sogenannten Lagerungsbukett beitragen. Besonders hohe DMS-Konzentrationen wurden in älteren Riesling-Weinen festgestellt

Factors affecting the reproducibility of fermentation of grape juice and of the aroma composition of wines 1. Grape maturity, sugar, inoculum concentration, aeration, juice turbidity and ergosterol

Gas chromatographic analysis was used for the investigation of some factors which determine the production of volatile wine components during fermentation. Especially the effect of "heterogenous" juice factors such as turbidity and air content were investigated in respect of fermentation rate and the production of fatty acids, fusel alcohols and esters. lt was shown that the fermentation lag of clear filtered and de-aerated grape juices could be prevented by small ergosterol additions before inoculation. A marked similarity was observed in the chromatograms of wines from fermentations of clear juices which were stimulated either by air or by ergosterol. Grape maturity proved to be a major factor affecting the production of volatile acids, alcohols and esters during fermentation. Fermentations of de-aerated and clear filtered juice with an addition of 0.5 g bentonite/l yielded wines with the best scores an sensory evaluation.Maßgebliche Faktoren für die Reproduzierbarkeit der Vergärung von Traubenmostund die Aromazusammensetzung von WeinI. Traubenreife, Zucker, Konzentration des lnokulums, Luft, Klarheit des Mostesund ErgosterinEinige Faktoren, welche die Bildung flüchtiger Weininhaltsstoffe bei der Gärung beeinflussen, wurden gaschromatographisch untersucht. Besonders die Wirkung „heterogener" Faktoren im Traubenmost, wie zum Beispiel Trübung und Luftgehalt, auf die Gärungsgeschwindigkeit und die Bildung von Fettsäuren, Fuselalkoholen und Estern wurde untersucht. Es wurde gezeigt, daß die Gärungsverzögerung bei klarfiltrierten und entlüfteten Traubensäften durch die Zufügung kleiner Mengen von Ergosterin vor der Inokulation verhindert werden kann. Wurde die Gärung von geklärtem Most durch Luft oder durch Ergosterin angeregt, so zeigten die Chromatogramme der Weine eine starke Ähnlichkeit. Die Traubenreife erwies sich als der wichtigste Faktor, der die Bildung von flüchtigen Säuren, Alkoholen und Estern bei der Gärung beeinflußt. Die Vergärung von entlüftetem und klarfiltriertem Most mit Zusatz von 0,5 g Bentonit/l ergab Weine, die bei der Weinprobe die höchsten Punktezahlen erhielten

Classification of White Cultivar Wines by Origin using Volatile Aroma Components

Stepwise discriminant analysis was applied to gas chromatographic data of some volatile compounds obtmiieabjiTreonextracliOii"of dry white table wines. By means of this statistical method, successful classifications according to origin of Colombar wines from two regions, and Chenin blanc wines from three regions, were obtained. The components with the highest discriminatory value were i-amyl acetate, hexyl acetate and i-butanol, in the case of the Colombar wines and hexanol and 2-phenyl ethanol in the case of the Chenin blanc wines

Differentiation between Wines Originating from Different Red Wine Cultivars and Wine Regions by the Application of Stepwise Discriminant Analysis to Gas Chromatographic Data

Stepwise discriminant analysis (SDA) was applied to gas chromatographic data of some volatile compounds extracted with freon from red wines. By means of this statistical method, Pinotage and Cabernet Sauvignon wines (1978 vintage) could be classified into separate groups, the most effective variables being hexanol and i-amyl acetate. Pinotage wines from three, and Cabernet Sauvignon wines from two localities (1979 vintage) were subjected to classification according to origin. Successful classifications were obtained using the variables ethyl acetate, ethyl caprate, i-amyl acetate as well as a compound tentatively identified as i-valeric acid

Objective quality rating of Pinotage wine

Relationships between wine composition and three quality parameters were investigated employing a linear multiple regression statistical model. For this purpose a least squares curve fitting computer programme was applied to analyses of 17 Pinotage wines for 6 fatty add esters. Overall quality, taste and aroma ratings were determined by a taste panel and utilized as dependent variables. lt was found that 2 esters viz. n-hexylacetate and ethyl-n-octanoate allowed excellent prediction equations to be set up for the quality ratings when incorporated into multiple regression equations.Objektive Beurteilung der Weinqualität bei der Sorte PinotageDie Beziehungen zwischen der Weinzusammensetzung und drei Parametern der Weinqualität wurden untersucht, wobei das statistische Modell einer mehrfachen linearen Regression verwendet wurde. Zu diesem Zweck wurden die bei 17 Weinen der Sorte Pinotage gewonnenen Analysenergebnisse über 6 Fettsäureester in ein Computerprogramm zur optimalen Kurvenanpassung eingegeben. Durch ein Gutachtergremium wurden die Gesamt-Weinqualität, der Geschmack und der Geruch bewertet; die Daten dieser Qualitätsbeurteilung wurden als abhängige Veränderliche benützt. Es wurde festgestellt, daß 2 Ester, nämlich n-Hexylacetat und Äthyl-n-octanoat eine ausgezeichnete Vorhersage der Weinqualität ermöglichten, wenn ihre Werte in Mehrfachregressions-Gleichungen eingesetzt wurden

Interactions between Grape Maturity Indices and the Quality and Composition of Chenin blanc and Colom bar Wines from Different Localities

Three grape maturity indices viz. degrees Balling (0 B), total titratable acidity (TT A) and the 0 B.pH product of musts were compared regarding their ability to predict optimum quality for Chenin blanc and Colombar wines. Comprehensive analytical data from 168 musts and corresponding wines for the 1978, 1979 and 1980 vintages from the Stellenbosch, Robertson and Lutzville areas were accumulated, and subjected to principal component analysis using variables and variable ratios selected by correlation to quality weighting. These results indicated that the two cultivars differed appreciably with respect to the value of all three measured indices. From this study it was not possible to select a specific index to predict optimum maturity in all cases. Optimum values for each index differed according to geographic locality