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Special thanks are due to Mr. H. Pool for assistance in the making of the wines and performing gaschromatographic analyses on them.

The quality of wine is without doubt largely dependent on the composition of the berries (Biol, 1977). In studies on grape quality, aspects of physiplogical, technological and industrial maturities have been covered by Kourakou (1974, 1977) and Marteau & Schaeffer (1978). These maturities refer to stages in the grape which are respectively, those where sugar production in the berry has generally ceased, where the grape has reached optimum quality and finally where grapes would give the most economical return. Burger (1977) pointed out the necessity for specifying parameters which could be used to classify grape quality. This also includes the aspect of grape maturity which is a most important facet of grape quality (Carrol el al., 1978) and regarded by some as being even more critical in this respect than viticultural practices (Slesinger, 1975).

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.

The surface grafting of cellulose nanocrystals (CNC) is a valuable tool to increase opportunities for their application. This work had several goals designed to improve CNC: reduction of hornification, increased re-dispersibility after CNC drying, and tuning of the surface graft to enhance the adsorption of particular molecules. To achieve this, the CNC surfaces were modified chemically with aromatic surface grafts using widely employed methods: the creation of urethane linkages, silylation and esterification. Even a low degree of grafting sufficed to increase water contact angles to as much as 96°. The analysis of water sorption isotherms showed that at high water activities, capillary condensation could be suppressed and hysteresis was decreased. This indicates that hornification was significantly suppressed. However, although the contact angles increased, the water sorption isotherms were changed only slightly because of reduced hysteresis. The grafts were not able to shield the surface from water vapour sorption. A comparison of the sorption isotherms of anisole and cyclohexane, sorbates with a similar surface area, showed that the sorption of anisole was three times higher than that of cyclohexane. The specific sorption of aromatic molecules was achieved and the most efficient methodology was the esterification of CNC with carboxylic acids containing a flexible linker between the aromatic moiety and ester bond.

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