The production of reduced-alcohol wine using glucose oxidase

In small scale trials, a process for the glucose oxidase (GOX) - catalysed oxidation of glucose in grape juice was developed and optimised. Up to 87% utilisation of glucose was achieved, producing wines of ca. 6.4% alcohol. This equates to a 40% reduction in alcohol content compared with conventionally processed wine. The effect of GOX -processing on the compositional, stability, and sensory properties of Müller-Thurgau and Riesling wines was investigated. Large amounts of gluconic acid are formed during GOX-treatment of juice, and a large portion of this is retained in the finished wine. In general GOX wines contained a higher concentration of esters and fatty acids, possibly due to alterations in juice amino acid composition. Relatively little change was observed in the concentration of the other volatile compounds. GOX wines show increased S0₂-binding power compared to control wines. GOX wines also had a more golden colour, possible due to increased quinone production and regeneration of oxidisable phenolic substrate. They were stable against browning after six months of bottle age, whereas control wines continued to brown throughout the two year period of monitored aging. GOX wine appeared to be stable with respect to 'pinking' reactions and other parameters examined. Although heat/cold tests suggest they are at more risk of developing a protein haze, no haze was observed. GOX-treatment of Riesling juice significantly modified the taste and appearance attributes of the resultant wine, while other flavour parameters were relatively unaffected. The exceptions were fruit aroma intensity and length of flavour, which were generally decreased in GOX wines primarily due to the juice aeration required during processing. Perceived viscosity and density were relatively unchanged in GOX wines, probably due to the high acidity which itself is a detracting characteristic. The effect of ethanol on the perception of fullness in white wine was investigated using a time-intensity methodology. A general pattern of increase in perceived viscosity and density occurs with increasing alcohol content up to 10 and 12% alcohol v/v respectively. The results support the anecdotal evidence that low-alcohol wines generally have reduced fullness compared with 'full-strength' wines, but this may not hold for wines above 12% and possibly 10% alcohol content. These findings raise some interesting questions on desirable alcohol levels for wine in general. In addition, the temporal parameters important in explaining perceived viscosity and density in white wine were determined.