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Influence Of Must Turbidity And Yeast Lees Content On Rebate Wine And Potstill Brandy Quality
F. P. van Jaarsveld1, S. Hattingh1, 2, J. Marais1 and M. Blom3
(1) ARC Infruitec-Nietvoorbij, Private Bag X5026, Stellenbosch 7599, South Africa
Key words: Must turbidity, yeast lees content, rebate wine (wine for brandy production), potstill brandy, brandy quality, acids, esters, higher alcohols.
The complete results of this study are contained in a scientific publication that is currently in print (Van Jaarsveld et al., 2005).
SUMMARY
The aims of the study were to identify a suitable must clarification technique, so as to obtain an optimum turbidity level with regard to rebate wine, as well as to determine the importance of chemical components (volatile components and long chain fatty acids) in rebate wine and rebate spirits quality, and to study the effect of yeast lees content on quality.
Various must clarification treatments were applied, namely no settling, settling with and without pectolytic enzyme, bentonite treatment, large- and small-scale centrifugation and whisking. Two yeast strains were compared, namely VIN 13 and 228. Wines distilled on a large-scale were compared to wines distilled on a small-scale. Different levels of yeast lees were also tested. Data as reported represent four years' investigation.
The treatments that produced the best quality rebate wine and rebate spirits, were settling, whisking, small-scale centrifugation and bentonite treatment. The treatments that resulted in the poorest quality products, were no settling and large-scale centrifugation. There is a definite correlation between treatment, concentrations of esters, higher alcohols and fatty acids, turbidity and overall rebate wine and/or rebate spirits quality.
INTRODUCTION According to current guidelines, rebate wine is prepared from must that is not entirely clarified. Techniques for the clarification of must differ between cellars and variation in rebate wine quality between techniques, as well as when using the same technique, occur frequently. Consequently there is a demand in the wine industry for clear guidelines stipulating the most suitable degree of turbidity, as well as the must clarification technique(s) that will produce the best results vis á vis rebate wine quality. Little is known about the impact of different must clarification techniques on the concentrations or composition of long chain fatty acids, esters, acids and higher alcohols, or the factors that may influence it under local conditions. Knowledge about the concentrations and composition of these groups of components could make it possible to make brandy with a more complex character in future. Various techniques for the clarification of musts are reported in literature, including bentonite treatment (Blade & Boulton, 1988; Görtges & Haubrich, 1992; Servilli et al., 2000; Spagna et al., 2000; Waters et al., 2000; Mesquita et al., 2001; Gómes-Plaza et al., 2002; Gökmen et al., 2003), pectolytic enzyme (Withy et al., 1993), whisking (Venter, 1991), centrifugation (Hamatschek & Nagel, 1993; Israel & Leufstedt, 1993; Kern et al., 1993) and settling (Boivin et al., 1998; Venter, 1991). It is well known that viticultural practices, method of harvesting, transport conditions, condition of the grapes, clarification/technological method, vinification processes, alcoholic fermentation conditions, yeast type, maturation processes, must composition and microbiological content may affect the chemical and sensory profiles of wine (Nykänen et al., 1968; Crowell & Guymon, 1969; Guymon & Crowell, 1969; Schreier et al., 1979; Shinohara, 1985; Piggot et al., 1992; Castro & Barroso, 2000; Lambrechts & Pretorius, 2000).
The aims of this study were to determine the influence of must turbidity on rebate wine- and rebate spirits quality and to recommend a suitable must clarification technique accordingly, as well as to determine the importance of long chain fatty acids, esters, acids and higher alcohols, and the effect of yeast lees content on these compounds and quality. EXPERIMENTAL PROCEDURE The study focussed on the effect of must turbidity on the chemical composition and quality of rebate wine and rebate spirits. Chenin blanc juice (3400 L) was obtained from Louwshoek Voorsorg Cellar (now Daschbosch Wine Cellar), Rawsonville and transported in tanks by road to the Nietvoorbij cellar where it was divided into portions, each of which was subjected to a different must clarification method, i.e. no settling, settling with and without pectolytic enzyme, bentonite and small-scale centrigufation. Large-scale centrifugation of must (1500 L) at 4000 rpm was also performed at Louwshoek cellar. Musts that did not receive any settling treatment, as well as must that had been subjected to small- and large-scale centrifugation, were immediately inoculated. Settling, bentonite and pectolytic enzyme treated musts were settled overnight at 18øC before inoculation. Whisking took place at the Louwshoek Cellar and whisked, but unsettled must (1500 L), was transported to Nietvoorbij, where the must was settled overnight at 18øC before inoculation. In a separate trial, musts subjected to no settling, settling with pectolytic enzyme, whisking and large-scale centrifugation treatments, also underwent large-scale treatments. Two yeast strains (VIN 13 and 228) were used and compared for each treatment. Both yeast strains VIN 13 and 228 were used separately in small-scale treatments, whereas only strain 228 was used in large-scale treatments. Di-ammoniumphosphate (50 g/hl) was added to all musts. All treatments took place in duplicate. For small-scale treatments musts were pumped to smaller tanks for suitable treatment and to 20 L canisters for inoculation and fermentation, and later distillation of rebate wine in 5 L quantities. For large-scale treatments musts were pumped over to 170 L tanks for suitable treatment, inoculation and fermentation and later distillation in 180 L potstills at Nietvoorbij.
Must turbidity was determined with a turbidity meter (Klett units), as well as spectophotometrically at 420nm. All rebate wine was left on the yeast lees and thoroughly stirred before distillation to rebate spirits. All rebate wine and unmatured rebate spirits samples were judged sensorially and analysed gaschromatographically for volatile esters, acids, higher alcohols and long chain fatty acids (Van Jaarsveld et al., 2005). Results were analysed statistically using the "Statistical Analysis System" (SAS version 8.2). RESULTS AND DISCUSSION For the purpose of this article only the essence of the results is presented. The following must clarification techniques produced the clearest musts and highest overall quality rebate wine and rebate spirits (Fig. 1): Settling with and without pectolytic enzyme treatment, bentonite treatment and small-scale centrifugation. Although whisk treatment also produced high quality rebate wine, the corresponding rebate spirits was of average quality. The following must clarification techniques produced the most turbid musts and lowest overall quality rebate wines and rebate spirits (Fig. 1): No settling and large-scale centrifugation. In rebate spirits, quality increases with increased yeast lees content for both yeast strains 228 and VIN 13 (the opposite trend is observed in rebate wine) (Fig. 2). In the case of VIN 13 a yeast lees addition of 1.5x the amount in VIN 13 fermented Chenin blanc musts, proved to be the optimum yeast lees content with regard to rebate spirits quality. In almost all treatments VIN 13 inoculated musts resulted in higher quality than yeast strain 228 (Fig. 1 and 2), but on the whole considering all treatments, it had a small impact on rebate wine (p ³ 0.05), but a bigger impact on rebate spirits quality (p £ 0.05) (data not shown). Overall comparison of large-scale (L) to small-scale distillations (s) for both rebate wine and rebate spirits, clearly indicate that the scale of distillation does not have a significant impact on quality (p ³ 0.05) (data not shown). On the whole, large-scale centrifugation delivered rebate wine and rebate spirits with more turbid musts and significantly lower quality than small-scale centrifugation (p £ 0.05) (data not shown). The reason for the difference in quality between large-scale and small-scale centrifugation lies in the fact that small-scale centrifugation at 9000 rpm produced clearer musts with a more optimal turbidity than large-scale centrifugation where centrifugation of musts are performed at lower speed (4000 rpm). The degree of turbidity and quality differences among all treatments on the whole, with or without pectolytic enzyme, for rebate wine as well as rebate spirits, was insignificantly small (p ³ 0.05) (data not shown). Consequently Chenin blanc musts did not benefit much from the enzyme treatments, because the cultivar also settles well spontaneously. This study confirms the findings of Rabbets (1989) and proves the importance of pre-trials before using pectolytic enzymes for the standard treatment of juice. The use of pectolytic enzymes did result in small quality improvements, however; it is known that the use of commercial pectic enzymes produces fruitier wines. With regard to rebate wine, significant positive (p £ 0.05) correlations between rebate wine quality and the volatile compounds ethyl butyrate, ethyl caprate, ethyl caprylate, ethyl acetate, ethyl caproate, hexyl acetate, isoamyl acetate, n-butanol, n-capric acid, n-caproic acid, n-butyric acid and n-caprylic acid occurred (Table 1). Significant negative (p £ 0.05) correlations between rebate wine quality and the following volatile compounds occurred: 2-phenyl ethanol, hexanol and isobutanol (Table 1). With regard to rebate spirits, significant positive (p £ 0.05) correlations were found between rebate spirits quality and the following volatile compounds: acetoin (data not shown), ethyl acetate, hexyl acetate, isoamyl acetate, n-butanol, n-capric acid, n-caproic acid (Table 1), ethylcaproate and n-caprylic acid (Fig. 2) occurred. Significant negative (p £ 0.05) correlations between rebate spirits quality and the following volatile compounds occurred: hexanol, isobutanol (Table 1) and isoamyl alcohol (Fig. 2). With regard to the long chain fatty acids, C12, C14, C16 en C18, a significant positive (p £ 0.05) correlation could only be found between lauric acid (C12) and rebate spirits quality (Fig. 2). CONCLUSIONS AND RECOMMENDATIONS The use of specific techniques to clarify grape musts is recommended seeing that all techniques/methods that are being used in practice and that were tested in this study, produced higher quality rebate wines and rebate spirits than untreated musts. The treatments delivering the highest quality rebate wine and rebate spirits were settling, whisking, small-scale centrifugation and bentonite treatments. The treatments that resulted in the lowest quality products, were no settling and large-scale centrifugation. There is definite relationship between treatment, concentrations of long chain fatty acids, esters, acids and higher alcohols, turbidity and overall rebate wine and/or rebate spirits quality. Treatments that produced higher concentrations of volatile and non-volatile compounds (in the case of positive correlations), also produced the highest quality products. In the case of negative correlations, treatments that resulted in higher quality products, produced lower concentrations of compounds (esters, acids, higher alcohols and long chain fatty acids). Treatments that resulted in cleaner musts (settling with and without pectolytic enzyme, whisking, bentonite and small-scale centrifugation), also resulted in the highest quality rebate wine and rebate spirits. Likewise treatments that produced the most turbid musts (no settling and large-scale centrifugation), resulted in the lowest quality products. In view of the results obtained by this study the following must clarification techniques are recommended: Settling, whisking, small-scale centrifugation and bentonite treatment. Yeast strain VIN 13 rather than 228 is recommended and a yeast lees addition of 1.5x the amount that normally occurs in VIN 13 fermented Chenin blanc musts. By following these guidelines, the highest quality rebate wine and rebate spirits can be made. ACKNOWLEDGEMENT The Agricultural Research Council and Winetech for financial support; Louwshoek Voorsorg Cellar (now Daschbosch Wine Cellar) for the supply, whisking and centrifugation of grape musts; Morné Lamont for statistical analyses, and Carin de Wet for word processing and electronic composition of tables. Further enquiries may be addressed to: Dr. Francois van Jaarsveld, tel. (021) 809-3052 (Int.: +27 21), email: vjaarsveldf@arc.agric.za. LITERATURE Blade, W. H. & Boulton, R., 1988. Adsorption of protein by bentonite in a model wine solution. Am. J. Enol. Vitic. 39 (3), 193-199. Boivin, S., Feuillat, M., Alexander, H. & Charpentier, C., 1998. Effect of must turbidity on cell wall porosity and macromolecule excretion of Saccharomyces cerevisiae cultivated on grape juice. Am. J. Enol. Vitic. 49 (3), 325-332. Castro, R. & Barroso, C. G., 2000. Behavior of a hyperoxidised must during biological aging of Fino sherry wine. Am. J. Enol. Vitic. 51 (2), 98-102. Crowell, E. A. & Guymon, J. F., 1969. Studies of caprylic, capric, lauric and other free fatty acids in brandies by gas chromatography. Am. J. Enol. Vitic. 20 (3), 155-163. Gökmen, V., Acar, J. & Kahraman, N., 2003. Influence of conventional clarification and ultrafiltration on the phenolic composition of golden delicious apple juice. J. Food Quality 26, 257-266. Gómez-Plaza, E., Gil-Muoz, R., López-Roca, J. M., Martínez-Cutillas, A. & Fernández-Fernández, J. I., 2002. Maintenance of colour composition of a red wine during storage. Influence of prefermentative practices, maceration time and storage. Lebensm.-Wiss. U. Technol. 35, 46-53. Görtges, S. & Haubrich, H., 1992. Fining agents and their effects on the treatment of fruit juice and wine. Fruit processing 2 (8), 119-122. Guymon, J. F. & Crowell, E. A., 1969. Gas chromatographic determination of ethyl esters of fatty acids in brandy or wine distillates. Am. J. Enol. Vitic. 20 (2), 76-85. Hamatschek, J. & Nagel, B., 1993. 100 Years of centrifuge engineering and the use of decanters for de-juicing of fruit. Fruit Processing 5, 163-167. Israel, S. & Leufstedt, G., 1993. Centrifugal juice extraction. Fruit Processing 5, 172-175. Kern, M., Guldenfels, W. & Sleveke, E., 1993. The use of decanters in modern fruit and vegetable extraction. Fruit Processing 5, 168-171. Lambrechts, M. G. & Pretorius, I. S., 2000. Yeast and its importance to wine aroma - a review. S. Afr. J. Enol. Vitic. 21 (special issue), 97-129. Lau, M. N., Ebeler, J. D. & Ebeler, S. E., 1999. Gas chromatographic analysis of aldehydes in alcoholic beverages using a cysteamine derivitisation procedure. Am. J. Enol. Vitic. 50 (3), 324-333. Marchand, S., De Revel, G. & Bertrand, A., 2000. Approaches to wine aroma: Release of aroma compounds from reactions between cysteine and carbonyl compounds in wine. J. Agric. Food Chem. 48, 4890-4895. Mesquita, P. R., Piçarra-Pereira, M. A., Monteiro, S., Loureiro, V. B., Teixeira, A. R. & Ferreira, R. B., 2001. Effect of wine composition on protein stability. Am. J. Enol. Vitic. 52 (4), 324-330. Nykänen, L., Puputti, E. & Suomalainen, H., 1968. Volatile fatty acids in some brands of whisky, cognac and rum. J. Food Sci. 33, 88-92. Piggot, J. R., Conner, J. M., Clyne, J. & Paterson, A., 1992. The influence of non-volatile constituents on the extraction of ethyl esters from brandies. J. Sci. Food Agric. 59, 477-482. Pons, M. N. & Wild, G., 1991. Monitoring volatile components production by a gas membrane sensor during alcoholic fermentation. Fruit Processing 1 (11), 174-176. Rabbets, T., 1989. Evaluasie van pektolitiese ensieme as afsakhulpmiddel vir druiwesap. Wynboer Tegnies. 31, 8. Schaefer, J. & Timmer, R., 1970. Flavor components in cognac. J. Food Sci. 35, 10-12. Schreier, P., Drawert, F. & Winkler, F., 1979. Composition of neutral volatile constituents in grape brandies. J. Agric. Food Chem. 27 (2), 365-372. Servili, M., de Stefano, G., Piacquadio, P. & Sciancalepore, V., 2000. A novel method for removing phenols from grape must. Am. J. Enol. Vitic. 51 (4), 357-361. Shinohara, T., 1985. Gas chromatographic analysis of volatile fatty acids in wines. Agric. Biol. Chem. 49 (7), 2211-2212. Spagna, G., Barbagallo, R. N. & Pifferi, P. G., 2000. Fining treatments of white wines by means of polymeric adjuvants for their stabilization against browning. J. Agric. Food Chem. 48, 4619-4627. Van Jaarsveld, F. P., Blom, M., Hattingh, S. & Marais, J., 2005. Effect of juice turbidity and yeast lees content on rebate wine and potstill brandy quality. S. Afr. J. Enol. Vitic. 25 (in druk). Venter, W. P., 1991. Hoe lyk 'n goeie rabatwyn en hoe word dit berei? Wynboer Tegnies 47, 4. Wagener, G. W. W., 1986. The effect of off-flavours of distilling wines on the quality of brandy. Wynboer Tegnies 16, 5-12. Waters, E., Dupin, I. & Stockdale, V., 2000. A review of current knowledge on polysaccharides which "protect" against protein haze in white wine. Aust. Grapegrower & Winemaker 438a, 13-16. Withy, L. M., Heatherbell, D. A. & Fisher, B. M., 1993. Red raspberry wine - effect of processing and storage on colour and stability. Fruit Processing 8, 303-307.
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Fig. 2
Effect of must clarification method on (A) ethylcaproate, (B) isoamyl alcohol, (C) n-caprylic acid and (D) lauric acid concentrations and overall rebate spirits quality. (A), r = 0.47 and p = 0.0161; (B), r = -0.70 and p = <0.0001; (C), r = 0.56 and p = 0.0031; (D), r = 0.54 en p = 0.0045. Every symbol represents the average data of four vintages. Treatments: 1, 1.5x yeast lees 228; 2, 1.5x yeast lees VIN 13; 3, 1x yeast lees 228; 4, 1x yeast lees VIN 13; 5, 2x yeast lees 228; 6, 2x yeast lees VIN 13; 7, settling (+P) 228 (L); 8, settling (+P) 228 (s); 9, settling (+P) VIN 13 (s); 10, settling (-P) 228 (s); 11, settling (-P) VIN 13 (s); 12, bentonite 228 (s); 13, bentonite VIN 13 (s); 14, no settling 228 (L); 15, no settling 228 (s); 16, no settling VIN 13 (s); 17, no yeast lees 228; 18, no yeast lees VIN 13; 19, large-scale centrifugation 228 (L); 20, large-scale centrifugation 228 (s); 21 large-scale centrifugation VIN 13 (s); 22, whisk 228 (L); 23, whisk 228 (s); 24, whisk VIN 13 (s); 25, small-scale centrifugation 228 (s); 26, small-scale centrifugation VIN 13 (s). s, Small-scale distillation; L, large-scale distillation; -P, no pectolytic enzyme; +P, with pectolytic enzyme; VIN 13, yeast strain VIN 13 and 228, yeast strain 228.
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