The effect of juice turbidity and yeast lees content on rebate wine and potstill brandy quality

Project Number
WW 09-03

Project title
The effect of juice turbidity and yeast lees content on rebate wine and potstill brandy quality

Project leader
Van Jaarsveld, F P

Team members
Bosman, M

Project description
The aim of this project is to study the effect of different must clarification methods on must turbidity and levels of long-chain fatty acids, esters, acids, higher alcohols and quality of rebate wines and rebate spirits, and to assess to what extent these components contribute to the quality of local rebate spirits.

The juice clarification treatments applied during 2000 included no settling, settling, whisk, large – and small scale centrifugation, and bentonite treatments. Yeast strain 228 was compared to Vin 13, as well as large-scale to small-scale distillation and no enzyme to the use of pectolytic enzyme. The chemical and sensorial data of the 2000 rebate wines and spirits are discussed in the present report.

Most treatments that yielded the best overall quality rebate wines, also yielded the highest quality rebate spirits, i.e. whisk (small-scale distillation) (Vin 13; 228), settling (with pectolytic enzyme) (small-scale distillation) (Vin 13) and small-scale centrifugation (small-scale distillation) (Vin 13) treatments (Table 8). These treatments also yielded the best quality rebate wines and spirits in previous vintage years. Bentonite treatment did, however, not feature as one of the top quality treatments for the 2000 vintage as in previous years. It is interesting to note that some of the different levels of yeast lees tested, yielded high quality products for the 2000 vintage, whereas, generally, low quality was observed for the previous vintage. No-settling and large-scale centrifugation yielded, as in previous years, the lowest observed quality rebate wines, as well as rebate spirits.

Treatments that yielded the highest quality rebate spirits were generally also accompanied by low must turbidity levels and high ester concentrations. Small differences in quality between Vin 13 and 228 were observed (generally slightly higher for Vin 13 except for the lowest quality products); which were generally also reflected in higher total ester concentrations, and with generally lower levels of total acid and higher total higher alcohol levels for Vin 13. The relationship between rebate spirits ester levels for Vin 13 and 228 were not as clear as reported for the 1999 vintage, probably due to the relatively low observed ester levels in the 2000 vintage. Increased ester and acid concentrations were associated with increased yeast lees addition, and, contradictory to the 1999 vintage, caused a difference in rebate spirit quality. No relationship was found between volatile components, quality and increased yeast lees content for rebate wines.

As reported for the 1999 vintage year, little or no difference could be found in quality between treatments with or without enzyme, with enzyme treatments giving slightly higher quality and ester concentrations, but lower total acid and alcohol concentrations.

Small-scale centrifugation yielded, as reported in the 1999 vintage, less turbid musts, higher total ester content, generally higher levels of the other volatile components, and higher quality products than large-scale centrifugation.

Large-scale distillations generally yielded slightly lower levels of total higher alcohols, acids and total esters in rebate wine, and slightly higher levels of total higher alcohols, but lower levels of acids and esters in rebate spirits, as compared to corresponding small-scale distillations. Coupled to this is the fact that lower quality products were obtained from large-scale distillations (not as clear for rebate wines). Results supported those of the 1998 vintage, but not entirely those of the 1999 vintage.

No relationship could be found between rebate spirits quality and the concentration of long-chain fatty acids, confirming results of the 1998 vintage.

The relationship between the different treatments, chemical composition and turbidity was not always as evident in rebate wines as in rebate spirits. This might have to do with ester limits and it is suggested that further investigations must be conducted to identify upper/lower cut-off limits for esters for producing rebate wines and spirits of higher quality.

Van Jaarsveld, F P. 2002. Invloed van mostroebelheid en gismoerinhoud op rabatwyn- en potketelbrandewynkwaliteit. Paper presented at the 26th National Congress of the South African Society for Enology and Viticulture. 13-15 November, Somerset West, South Africa


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