The possible effect of oxidation [processing with or without sulfur dioxide (±S0₂)] and of pre-ultrafiltration treatment of juices with enzymes and fining agents on flux, and on juice color, composition and stability was investigated. White Riesling juice was ultrafiltered with a Romicon system operated with a nominal molecular weight cut-off (MWCO) of 10,000 daltons. In addition, UF White Riesling juices processed ±S0₂, were stored for 2 months (1985 vintage) and 12 months (1984 vintage) at 2°C and 20°C, and evaluated by a trained panel using descriptive analysis. Pre-UF treatment with enzymes and fining increased flux. Sediment formation and instability to heat testing of UF permeates processed -S0₂ was prevented with pre-fining. Up to 99% of protein, 90% of pectin, 84% of color and low variable phenolics were retained by the membrane of 10,000 dalton MWCO. During UF there is a significant increase in the soluble protein and water soluble pectin passing through the membrane with increasing volume concentration ratio (VCR, process time). It is concluded that it is not only the amount but the nature/state of compounds such as proteins, phenolics, pectins, and their interaction that results in instability. UF juices processed with minimum oxidation and stored for 12 months had lower intensity aroma (apple/apple cider, sweet, and honey/caramel) and overall intensity flavor by mouth descriptors than those processed with oxidation. Moreover, juices processed with minimum oxidation and stored for two months (1985 vintage) had significantly lower intensity of apple/apple cider, sweet, honey/caramel aroma descriptors when compared to those processed with oxidation. There was no effect of temperature of storage on any of the aroma and flavor-by-mouth descriptors for the 1985 juice after two months of storage. Only one aroma descriptor (vegetative) was significantly increased for the 1984 White Riesling juice after 12 months at 2°C. This indicates the possibility that UF juices may be stored at higher temperature (20°C) for less cost with minimal changes in aroma and flavor. White Riesling (WR) and Gewurztraminer (GEW) wines were ultrafiltered with Romicon and Millipore pilot-scale systems, respectively. The effect of ultrafiltration (UF), membrane MWCO from 10,000-50,000 daltons, and of VCR on composition and wine stability was investigated. The effect of 1) pilot-scale UF processing and Bentonite fining on WR and GEW wines, and 2) commercial-scale UF processing on GEW wine was sensorially evaluated by a trained panel using descriptive analysis. UF processing significantly reduced color (A [subscript 420nm]), total phenol, protein and heat/cold test (HOT) haze of both WR and GEW wines. Stability to HOT haze formation was obtainable with MWCO of 10,000 daltons, but trace instability can remain. With increasing VCR (process time) there was a significant decrease in membrane retention of color (A [subscript 420nm]), protein, and HCT haze formation in the WR wine and the color (A [subscript 420nm]) of the GEW wine. UF processing of the WR wine significantly decreased the perception of overall aroma intensity, fruity, fresh fruity citrus, floral, sweet and honey/caramel character but it also increased the intensity of the vegetative aroma descriptor when compared to the control unfiltered WR wine. In addition, significant differences were detected for these descriptors between the bentonite-fined WR wine and the ultrafiltered WR wine except for fresh fruity citrus and honey/caramel which were less intense in the ultrafiltered WR ultrafiltered WR wine. UF processing of GEW wine significantly decreased the intensity of fruity, fresh fruity aroma descriptors; and increased the chemical aroma descriptor compared to the control unfiltered GEW wine. However, no significant differences were detected for these descriptors between the bentonite fined GEW wine and the ultrafiltered GEW wine except for fresh fruity which was less intense in the ultrafiltered GEW wine. Commercial processing of GEW wine by UF did not have any significant effect on the aroma and flavor by mouth descriptors evaluated as compared to standard processing procedures. / Graduation date: 1988