P. C. Van Rooyen

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.

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.

The effect of irrigation practices in the Breë River Valley on the salt content of a small river

SummaryThe effect of varying irrigation return flow volumes as a possible explanation for the fluctuations in the mean monthly baseflow TDS content of a tributary in the Breë River Valley (South-Western Cape Province, Rep. of South Africa) has been investigated. A conceptual computer model was used to simulate the movement of water and solutes in 769 ha of soil in an area where vineyards are irrigated intensively. Important input requirements of the model are the physical and chemical properties of the irrigated soils, consumptive use data, and root distribution patterns.It was found that the present system of vineyard irrigation which involves a large amount of water being applied as a pre-bud-burst irrigation in late August or early September, followed by more or less fixed amounts of water being applied at set frequencies during the rest of the irrigation season, results in deep percolation losses and accompanying salt loads which are much bigger during the last six months than during the first six months of the year. The results further indicate that during the period January to June, capillary rise will exceed deep percolation. On a half yearly time basis, these computer predictions were in fair accordance with the observed TDS content of the receiving river, which for three consecutive years (1978–1980) have been substantially higher during the period July to December than from January to June. However, on a monthly time basis, it was found that the fair comparison between predicted (in the irrigation return flow) and observed (in the river) mean monthly TDS contents for the months July to December does not apply to the period January to June.

Interactions between Grape Maturity Indices and Quality for Pinotage and Cabernet Sauvignon Wines from Four Localities

Three grape maturity indices viz. degrees Balling (OB), OB total titratable acid (TT A) ratio and the OB.pH product of musts were compared regarding their ability to predict optimum quality for Cabernet Sauvignon and Pinotage wines. Comprehensive analytical data from 128 musts and corresponding wines for the 1979 and 1980 vintages from the Stellenbosch, Durbanville, Lutzville and Robertson areas were subjected to principal component analysis using variables and variable ratios selected by correlation to quality weighting. The results indicated that 0B alone could not perform the function of a grape maturity index for predicting optimum quality. In the case of the OB/TT A index, the range wherein maximum wine quality occurred was too wide to be of practical value in this instance. The 0B.pH index gave a narrower optimum range, and in contrast to the two other indices gave similar results for both cultivars.

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.

Polysaccharides in molasses meal as an ameliorant for saline-sodic soils compared to other reclamation agents☆

Abstract A study was undertaken to evaluate the effect of polysaccharides on certain important physical properties of an irrigated soil compared to other well-known brack-soil reclamation agents, viz. gypsum, sulphur, potassium sulphate and manure. Field-plot trials were carried out on a sandy loam to sandy clay loam being predominantly saline-sodic, but the plots were freely interspersed with spots of a sodic nature. The source of the polysaccharides used was molasses meal, a waste product of the sugar-cane processing industry, which is mainly used as a stock feeding concentrate. The experiment was conducted under rigidly arid climatic conditions in the southern Cape Province, and a minimum of irrigation water was used. Five months after application of the ameliorants soil samples were taken and analysed. Effects on infiltration rate, modulus of rupture and bulk density of soil briquettes, aggregate stability, pH, total salt content of the saturated soil paste extract as well as sodium adsorption ratio, Na K ratio, chloride content and carbonate plus bicarbonate contents thereof, were measured. Results proved the instant as well as long-term effectiveness of molasses meal and its superiority to the other ameliorants. Physical soil properties were drastically improved after a relatively short period of presence of molasses meal in the soil whilst total salt content, pH and SAR remained unchanged. The only chemical alterations noted in the case of this treatment were in the Na K ratio and in the carbonate plus bicarbonate content. The former was attributed to the relatively high content of K+ in the molasses meal and the latter to intense microbial activity. However, neither the much heavier application of K+ by potassium sulphate causing a very favourable Na K ratio, nor an equal amount of manure could bring about the same improvement in physical soil conditions as did molasses meal. So it was tentatively concluded that the aggregating powers ot the polysaccharides in molasses meal may be stronger than the dispersing forces of the Na+-ions adsorbed in these soils.

Long-term effects of five ameliorants on a saline-sodic soil of South Africa

Abstract The effects of five ameliorants for saline-sodic soil reclamation on certain chemical and physical soil properties over a four-year period of observation are reported. Of these ameliorants, three are conventionally used (gypsum, sulphur, manure); the other two are for this purpose either unusual (potassium sulphate) or relatively unknown (molasses meal). Results published in a previous paper demonstrated that molasses meal had a very rapid-acting favourable effect on most soil physical properties whilst soil chemical conditions remained essentially unchanged. The effect on physical properties was presumably due to soil aggregation by the polysaccharide component of molasses meal. As a follow-up this paper shows, however, that this aggregation does not last long; the rigidly arid climatic conditions under which this experiment was carried out apparently do not favour the preservation of structural bonds consisting of polysaccharide gums. Consequently, a gradual decline of structural conditions took place after the second year. Although initially not as effective as molasses meal, gypsum and sulphur retained their favourable influence on physical properties over a longer period. Potassium sulphate and farmyard manure provided virtually no benefits.

The Effect of Fermentation Time (as Induced by Fermentation and Must Conditions) on the Chemical Profile and Quality of a Chenin blanc Wine

Pattern recognition and simple factorial analyses were applied to chemical profiles determined on wines resulting from an experiment in which the effect of grape solids, assimilable nitrogen, bentonite and fermentation temperature levels as well as culture aeration on total fermentation time was investigated. It was found that fermentation times of the untreated Chenin blanc must could be shortened considerably by increasing grape solid levels and/ or nitrogen as well as temperature. However, it was established that the speeding up of fermentation at sub-optimal assimilable nitrogen levels leads to wines relatively high in higher alcohols and low in esters.

ESTIMATES OF METABOLIZABLE ENERGY NEEDS FOR MAINTENANCE AND GAIN IN BEEF STEERS OF FOUR GENOTYPES

Seven young steers of each of the breeds Africander, Drakensberg, Hereford and Simmental were fed at different feeding levels from near maintenance to near ad lib. for 120 days. Empty-body-weight (EBW) gains were measured and related to ME intake and indirect estimates of changes in body composition. The equation ME= a W 0.75 (1 + b′G), fitted to the data, predicted lower maintenance needs for Africander and Simmental but relative weight gains were not significantly different. At 300 kg the live-weight predictions of live-weight gain by the above equation and the metabolizable energy (ME) system were similar.

Evaluation of the Nietvoorbi j Wine Score Card and Experimental Wine Panelists Utilizing Pattern Recognition Techniques

Principal component analysis (PCA) was applied to four cultivar wines, submitted repetitively amongst more than 450 experimental wines, to a sensory evaluation panel of 18 members who used a scoring system comprising overall wine quality and 11 wine descriptors. Inconsistent judges could be eliminated by the evaluation of scatter diagrams. After eliminating 11 judges, the scores of the remaining 7 were used to evaluate the score card in terms of weights placed on individual descriptors in a multiple regression equation, which related the 11 parameters to overall quality scores. Deviations from actual score card weights are discussed in terms of previous PCA analyses, and it is argued that both cultivar and the composition of a mixed data set with respect to these factors, could affect the relative importance of certain parameters. Fitting a similar equation to a large data set consisting of about 480 wines, comprising 23 different cultivars, confirmed the need for further investigations concerning relative score card weights, as well as a critical evaluation of score card parameters for evaluating widely diverging experimental wines.